HVAC Systems - Manual Cadillac Escalade GMT800

Fastener Tightening Specifications

Heating Ventilation And Air Conditioning Fastener Tightening Specifications

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Test Description

The numbers below refer to the step numbers on the diagnostic table.

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1. 3. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 5. Determine if the HVAC Control Module, Body Control Module or Powertrain Control Module have set DTCs which may affect HVAC operation are present.
3. 6. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
4. 7. Answer Yes if the first 3 characters of the DTC name begins with B10; regardless of the last 2 characters.

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Scan Tool Data Definitions

A/C High Side Pressure: The scan tool displays 0-3450 kPa (0-500 psi). The voltage applied to the PCM input from the A/C refrigerant pressure sensor is converted to a pressure value.

A/C High Side Pressure: The scan tool displays 0-5 volts. The voltage applied to the PCM input for the A/C refrigerant pressure sensor.

A/C Switch: The scan tool displays On/Off. The scan tool displays On when the A/C request switch is active. The scan tool displays Off when the A/C request switch is inactive.

AC/Heater Door Actual: The scan tool displays 0-255 Counts. The voltage applied to the HVAC control module input for the mode door position is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

AC/Heater Door Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired mode door position as determined by the HVAC control module.

AC/Heater Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

A/C Relay Command: The scan tool displays On/Off. The scan tool displays the control decision for the compressor clutch relay output as determined by the PCM.

A/C Request Signal: The scan tool displays Yes/No. The scan tool displays Yes when the PCM receives a class 2 message from the HVAC control module to engage the A/C compressor clutch. The scan tool displays No when the PCM receives a class 2 message from the HVAC control module to disengage the A/C compressor clutch.

Air Inlet Drive Motor: The scan tool displays Fresh Air or Recirc. The scan tool displays Recirc. when the recirculation actuator is closed.

Air Mix Door Left Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired left air temperature door position as determined by the HVAC control module.

Air Mix Door Right Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired right air temperature door position as determined by the HVAC control module.

Battery Voltage: The scan tool displays 0-25 volts. The voltage measured from the battery positive voltage circuit and the ground circuit of the HVAC control module.

ECT Sensor: The scan tool displays -39 to 140°C (-38 to 284°F). The voltage applied to the PCM input from the engine coolant temperature sensor is converted to a temperature value.

ECT Sensor: The scan tool displays 0-5 volts. The voltage applied to the PCM input for the engine coolant temperature sensor.

Ign. Since Current DTC: The scan tool displays 0-100. The number of the ignition cycles since the setting of the most recent current diagnostic trouble code (DTC).

Left Mix Door Actual: The scan tool displays 0-255 counts. The voltage applied to the left air temperature door position input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Left Mix Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Left Solar Sensor: The scan tool displays 0-255 counts. The voltage applied to the left sunload input of the BCM is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Left Temp. Detent Pos.: The scan tool displays 0 to 18. The scan tool displays the position of the left air temperature switch.

Mode Door Actual: The scan tool displays 0-255 counts. The voltage applied to the auxiliary mode door position input of the auxiliary HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Mode Select Position: The scan tool displays Off, Defrost, Heater, Htr/Def, Bi-Level, Panel. The scan tool displays the state of mode operation.

Pressure Cycle Switch: The scan tool displays Low Pressure/Normal. The current state of the input from the A/C low pressure switch. The scan tool displays Low Pressure when the switch is open and displays Normal when the switch is closed. The low pressure switch opens when low side pressure decreases to approximately 151 kPa (22 psi) and closes when the low side pressure increases to approximately 275 kPa (40 psi).

Rear Blower Speed: The scan tool displays Off, Low, Med or High. The commanded state of the auxiliary blower motor as determined by the auxiliary HVAC control module.

Rear HVAC: The scan tool displays Disabled/ Enabled. The scan tool displays Disabled when the HVAC control module is in the front defrost mode. The HVAC control module transmits a class 2 message to the auxiliary HVAC control module in order to disable auxiliary operation while in the defrost mode. The scan tool displays Enabled in all other modes of operation.

Rear HVAC Fan Down Switch: The scan tool displays Active or Inactive. The scan tool displays Active when the fan down switch is pressed. The scan tool displays Inactive when the fan down switch is not used.

Rear HVAC Fan Speed: The scan tool displays Off, Low, Med or High. The commanded state of the auxiliary blower motor as determined by the auxiliary HVAC control module.

Recirculate Switch: The scan tool displays On/Off. The scan tool displays On when the recirculation switch is active. The scan tool displays Off when the recirculation switch is inactive.

Right Mix Door Actual: The scan tool displays 0-255 counts. The voltage applied to the right air temperature door position input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Right Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Right Temp. Detent Pos.: The scan tool displays 0 to 18. The scan tool displays the position of the right air temperature switch.

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Circuit Description

The following DTCs are for the HVAC door actuators

1. B0263 is for the mode actuator.
2. B0408 is for the left air temperature actuator.
3. B0418 is for the right air temperature actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5 volt signal increases the door position. A 0 volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5 volt signal to the door actuator and motor rotation stops. The ignition 3 voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit.

Conditions for Running the DTC

1. Source voltage is 8.7-16.5 volts.
2. The ignition is ON.
3. The HVAC control module commands the actuator to move.

Conditions for Setting the DTC

The actual door position is not near the commanded door position.

Action Taken When the DTC Sets

The HVAC control module does not command the actuator to move for the remainder of the ignition cycle.

Conditions for Clearing the DTC

1. The DTC becomes history during the next ignition cycle in which the HVAC control module no longer detects a stall condition.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

1. If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.
2. Inspect the appropriate door and door actuator for the following conditions: A misaligned door actuator Binding linkages A binding door An obstruction that prevents the door actuator from operating within the full range of motion

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. Determines if the HVAC door actuator is stalled.
2. 3. Applies control circuit voltages to the input of the HVAC door actuator.

The following DTCs are for the HVAC door actuators

1. B0414 is for the left air temperature actuator.
2. B0424 is for the right air temperature actuator.
3. B3770 is for the mode actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5-volt source voltage to the potentiometer on the 5-volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The module converts the voltage value to a count value where 1-volt is approximately equal to 51 counts.

The HVAC control module calibrates the travel range of the HVAC door actuators when it is initially powered by the battery positive voltage circuit. During calibration, the module commands the actuators in each direction until door travel is stopped. The module stores the minimum door positions and the maximum door positions of each actuator into memory. The total travel range is calculated by subtracting the minimum door position from the maximum door position.

The door actuators can be calibrated again with a scan tool.

1. Battery voltage is 8.7-16.5 volts.
2. The ignition is ON.

The DTC sets when one of the following conditions are present

1. The actual door position value for the actuator is less than 5 counts.
2. The actual door position value for the actuator is greater than 250 counts.
3. The actuator fails calibration because the calculated travel range value is too great or too small.

1. If the DTC sets because the actual door position value is out of range, the HVAC control module will command the actuator to a default position.
2. If the DTC sets because the actuator failed a calibration, the HVAC control module will attempt to calibrate the motor in the next transition from OFF to RUN mode.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.
2. If the DTC sets following a calibration of the door actuator, inspect the door and the actuator for the following conditions: A misaligned actuator Broken linkages or binding linkages A broken door or a binding door An obstruction that prevents the door from operating within the full range of motion Missing seals to the door Poor connections at the harness connector of the door actuator
3. If a signal circuit of an actuator is short to ground and the resistance across the internal potentiometer is low, then this condition could cause a multiple DTC concern.

The numbers below refer to the step numbers on the diagnostic table.

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1. 3. At least two of the DTCs must be set as current DTC to ensure correct diagnosis. If only one DTC is present then the answer is No.
2. 5. Tests for the proper operation of the circuit in the low voltage range.
3. 6. Tests for the proper operation of the circuit in the high voltage range. If the jumper fuse opens when you perform this test, the circuit is shorted to ground.
4. 7. Tests for a short to voltage in the 5-volt reference circuit.
5. 8. Tests for a high resistance or for an open in the low reference circuit.
6. 9. This step tests for an open on the low reference circuit that is common to all of the actuators. Choose the easiest HVAC door actuator that set a DTC to start the diagnosis.
7. 10. Disconnecting each actuator, one at a time, isolates the disconnected actuators signal circuit from the 5-volt reference circuit that is common to all the actuators.

The ignition 3 voltage circuit is a discrete input to the HVAC control module. The HVAC control modules uses the input to determine that the ignition switch is in the RUN position. When the ignition switch is in the RUN position, ignition voltage is applied to the input.

1. Source voltage is 8.7-16.5 volts.
2. The HVAC control module receives a RUN power mode message from the BCM over the class 2 serial data circuit.

The HVAC control module does not detect ignition voltage on the ignition 3 voltage input.

The HVAC control module will continue to operate using the class 2 power mode messaging.

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1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The powertrain control module (PCM) monitors the high side refrigerant pressure via a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is too high the PCM will not allow the A/C compressor clutch to engage.

The PCM detects an A/C request.

1. The A/C refrigerant pressure sensor signal is less than 0.1 volts for 5 seconds.
2. The A/C refrigerant pressure sensor signal is greater than 4.9 volts for 5 seconds.

The malfunction indicator lamp (MIL) will not illuminate.

1. The DTC will become history if the PCM no longer detects a failure.
2. The history DTC will clear after 40 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

For an intermittent, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

The numbers below refer to the step numbers on the diagnostic table.

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1. 3. Tests for the proper operation of the circuit in the low voltage range.
2. 4. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
3. 5. Tests for a short to voltage in the 5-volt reference circuit.
4. 6. Tests for a high resistance or an open in the low reference circuit.

Important: Review the system operation in order to familiarize yourself with the system functions. Refer to the following information

1. «AIR DELIVERY DESCRIPTION AND OPERATION»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__air-delivery-description-and-operation)
2. «AIR TEMPERATURE DESCRIPTION AND OPERATION»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__air-temperature-description-and-operation)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. The A/C compressor will not operate in cold outside air temperatures. Refer to «AIR TEMPERATURE DESCRIPTION AND OPERATION»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__air-temperature-description-and-operation) .
5. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
6. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped. Blocked or damaged air inlet or outlet vents.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
2. «HVAC COMPRESSOR CLUTCH DOES NOT DISENGAGE»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
3. «BLOWER MOTOR ALWAYS ON»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
4. «BLOWER MOTOR INOPERATIVE»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
5. «BLOWER MOTOR MALFUNCTION»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
6. «BLOWER MOTOR ALWAYS ON - AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
7. «BLOWER MOTOR INOPERATIVE - AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
8. «BLOWER MOTOR MALFUNCTION - AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
9. Too Hot in Vehicle, See «Too Hot In Vehicle»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
10. «TOO COLD IN VEHICLE»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
11. «TOO HOT IN VEHICLE - AUXILIARY (WITH HEAT AND A/C)»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual) or «TOO HOT IN VEHICLE - AUXILIARY (A/C ONLY)»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
12. «TOO COLD IN VEHICLE - AUXILIARY (WITH HEAT AND A/C)»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual) or «TOO COLD IN VEHICLE - AUXILIARY (A/C ONLY)»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
13. «AIR DELIVERY IMPROPER»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
14. «AIR DELIVERY IMPROPER - AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual)
15. AIR RECIRCULATION MALFUNCTION
16. LEAK TESTING in Heating, Ventilation and Air Conditioning
17. NOISE DIAGNOSIS - BLOWER MOTOR in Heating, Ventilation and Air Conditioning
18. NOISE DIAGNOSIS - AIR CONDITIONING (A/C) SYSTEM in Heating, Ventilation and Air Conditioning
19. NOISE DIAGNOSIS - HVAC MODULE in Heating, Ventilation and Air Conditioning
20. ODOR DIAGNOSIS in Heating, Ventilation and Air Conditioning

A/C compressor clutch will not engage under the following conditions

1. The A/C high side line pressure is over 2957 kPa (429 psi).
2. The A/C low side line pressure is under 151 kPa(22 psi).
3. Throttle angle is at 100 percent.
4. Engine speed is more than 5500 RPM.
5. Engine coolant temperature (ECT) is more than 121°C (250°F).
6. Ambient air temperature is less than 5°C (40°F).

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F). The engine coolant indicator will illuminate at this temperature.
2. 3. This step ensures that the HVAC control module is receiving an input from the A/C switch.
3. 4. These actions will enable the A/C compressor to operate.
4. 5. This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test in Heating, Ventilation and Air Conditioning.
5. 7. The A/C low pressure switch parameter is out of range when the HVAC control module interprets the signal being below 151 kPa (22 psi).
6. 8. This action will simulate a closed switch condition. If the Pressure Cycle Switch parameter reads Low Pressure than there is a circuit condition or a condition with the HVAC control module.
7. 11. The A/C compressor relay output from the powertrain control module (PCM) is disabled if the A/C high side system pressure is interpreted to be higher than 2958 kPa (429 psi).

The number below refers to the step number on the diagnostic table.

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1. 2. These actions will disable the HVAC control module output to powertrain control module (PCM).

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step checks for continuous operation of the blower motor.
2. 3. The test lamp should not illuminate while connected to any of the blower motor control circuits when the blower motor switch is in the OFF position. Illumination of the test lamp during this step indicates a malfunctioning blower motor switch or a short to voltage on a blower motor control circuit.
3. 4. Test the blower motor control circuit that illuminated the test lamp in Step 3.

The numbers below refer to the step numbers on the diagnostic table.

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1. 6. This step tests the output from the blower motor switch. Loss of blower motor switch output would indicate a malfunctioning switch or a circuit malfunction in the supply voltage to the switch.
2. 7. There are two ignition 3 voltage circuits at the HVAC control module. Test the circuit that provides the supply voltage to the blower motor switch.

The numbers below refer to the step numbers on the diagnostic table.

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1. 5. This step tests the output of the blower motor switch in each speed position and through each blower motor control circuit.
2. 6. Test the circuit that did not illuminate the test lamp in Step 5.

The number(s) below refer to the step number(s) on the diagnostic table.

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1. 2. This step tests for auxiliary blower motor operation in the OFF setting.
2. 3. The rear auxiliary HVAC control assembly should not operate with the front auxiliary blower motor switch in the OFF position.

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step tests for auxiliary blower motor operation in any speed setting.
2. 8. This step determines if the malfunction is in the control side of the system.
3. 10. Test both the rear auxiliary HVAC control assembly chassis ground circuit and the ground circuit between the front and rear HVAC control assemblies.

The number(s) below refer to the step number(s) on the diagnostic table.

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1. 2. This step will determine if one or more blower speeds are inoperative.
2. 3. If the auxiliary blower motor operates correctly from the rear auxiliary HVAC control assembly, the auxiliary blower motor and auxiliary blower motor resistor assembly are functioning properly.
3. 4. This step tests for an open in one of the blower motor speed control circuits and determines if the auxiliary blower motor and auxiliary blower motor resistor are functioning correctly.

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The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step ensures that the primary HVAC system is functioning properly.
2. 5. If the condition does not occur when an A/C request has been made then you must bypass the A/C performance test procedures.
3. 6. Performing the Air Conditioning System Performance Test ensures that the A/C system is operating properly for further testing.
4. 7. This step ensures that the rear auxiliary HVAC control module is able to move the auxiliary air temperature actuator.
5. 8. This step ensures that the front auxiliary HVAC control assembly is able to move the auxiliary air temperature actuator.
6. 9. There is 2 ignition 3 voltage circuits for the rear HVAC control assembly. The circuit that needs to be tested is the circuit that supplies ignition 3 voltage to the auxiliary HVAC control processor. If this circuit is open the auxiliary mode and air temperature actuators will not move with in there full range of motion.
7. 12. There is 2 ignition 3 voltage circuits for the rear HVAC control assembly. The circuit that needs to be tested is wired between the left I/P fuse block and the rear HVAC control assembly.
8. 14. The circuit that is to be tested is wired between the rear auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in the AUX position.
9. 17. The circuit that is to be tested is wired between the front auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in any other position than AUX position.
10. 22. This step checks the output of the auxiliary HVAC control processor to the auxiliary air temperature actuator.

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step ensures that the primary HVAC system is functioning properly.
2. 5. Performing the Air Conditioning System Performance Test ensures that the A/C system is operating properly for further testing.

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step ensures that the primary HVAC system is functioning properly.
2. 5. If the condition does not occur when a heating request has been made then you must bypass the A/C compressor and cooling system diagnostic information.
3. 7. This step ensures that the rear auxiliary HVAC control module is able to move the auxiliary air temperature actuator.
4. 8. This step ensures that the front auxiliary HVAC control assembly is able to move the auxiliary air temperature actuator.
5. 9. There is 2 ignition 3 voltage circuits for the rear HVAC control assembly. The circuit that needs to be tested is the circuit that supplies ignition 3 voltage to the auxiliary HVAC control processor. If this circuit is open the auxiliary mode and air temperature actuators will not move with in there full range of motion.
6. 12. There is 2 ignition 3 voltage circuits for the rear HVAC control assembly. The circuit that needs to be tested is wired between the left I/P fuse block and the rear HVAC control assembly.
7. 14. The circuit that is to be tested is wired between the rear auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in the AUX position.
8. 17. The circuit that is to be tested is wired between the front auxiliary HVAC control assembly and the auxiliary HVAC control processor. The circuit is the position signal from the rear auxiliary HVAC control assembly for the auxiliary air temperature actuator. The circuit only provides a reference when the front auxiliary HVAC control assembly is in any other position than AUX position.
9. 22. This step checks the output of the auxiliary HVAC control processor to the auxiliary air temperature actuator.

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step ensures that the primary HVAC system is functioning properly.
2. 5. If the condition does not occur when a heating request has been made then you must bypass the A/C compressor and cooling system diagnostic information.

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1. The condition may be intermittent. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.
2. Inspect the air delivery system for the following conditions: A dirty HVAC air filter, if applicable An obstruction to the airflow Air leaks Misaligned air ducts Broken or binding linkages or doors

The numbers below refer to the step numbers on the diagnostic table.

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1. 2. This step tests for an inoperative auxiliary mode actuator in one mode positions or in the wrong mode positions from the front auxiliary HVAC control module.
2. 5. This step tests for an inoperative auxiliary mode actuator in one mode positions or in the wrong mode positions from the rear auxiliary HVAC control module.

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Re-Calibrating Actuators

When replacing the HVAC control module it will be necessary to allow the HVAC control module to perform a re-calibration process. When installing the HVAC control module be sure to perform the following

Important: Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.

1. Place the ignition switch to the OFF position.
2. Disconnect the scan tool.
3. Install the HVAC control module.
4. Re-connect all previously disconnected components.
5. Start the vehicle.
6. Wait 40 seconds for the HVAC control module to re-calibrate.
7. Verify that no DTCs have set as current DTCs.

When replacing the motor assembly it will be necessary to allow the HVAC control module to perform a re-calibration process. When installing the motor assembly be sure to perform one of the following

Important: Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.

Preferred Method (w/ Scan Tool)

1. Clear all DTCs
2. Place the ignition switch in the OFF position.
3. Install the motor assembly.
4. Re-connect all previously disconnected components.
5. Start the vehicle.
6. With the scan tool, initiate the Motor Re-calibration feature of the HVAC module Special Functions menu.
7. Verify that no DTCs have set as current DTCs.

Important: Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.

Alternate Method (w/o Scan Tool)

1. Clear all DTCs
2. Place the ignition switch to the OFF position.
3. Disconnect the scan tool.
4. Install the motor assembly.
5. Re-connect all previously disconnected components.
6. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
7. Re-install the HVAC/ECAS fuse.
8. Start the vehicle.
9. Wait 40 seconds for the HVAC control module to re-calibrate.
10. Verify that no DTCs have set as current DTCs.

Scheme 471

1. Remove the instrument cluster trim plate bezel. Refer to BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages, and Console.
2. Remove the instrument panel storage tray.
3. Remove the accessory switch assembly from the instrument panel. Refer to ACCESSORY SWITCH REPLACEMENT in Instrument Panel, Gages, and Console.
4. Remove the screws from the HVAC control assembly.
5. Remove the HVAC control assembly, with the following procedure: Release the retaining tabs. Pull the control head out of the instrument panel carrier.
6. Disconnect the electrical connectors from the HVAC control assembly.

Installation Procedure

Important: The Key should be in the off position when connecting the electrical connectors to ensure proper calibration.

Scheme 472

1. Connect the electrical connectors to the HVAC control assembly.
2. Install the HVAC control assembly.
3. Install the accessory switch assembly to the instrument panel. Refer to ACCESSORY SWITCH REPLACEMENT in Instrument Panel, Gages, and Console. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the screws from the HVAC control assembly. Tighten Tighten the screws to 1.9 N.m (17 lb in).
5. Install the instrument panel storage tray.
6. Install the instrument cluster trim plate bezel. Refer to BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages, and Console. Important: Do not adjust any controls on the HVAC control module while the HVAC control module is calibrating. If interrupted improper HVAC performance will result.
7. Start the vehicle and let run for one minute.

Scheme 473

1. Remove the I/P carrier. Refer to INSTRUMENT PANEL (I/P) CARRIER REPLACEMENT in Instrument Panel, Gages, and Console.
2. Disconnect the electrical connector (4) from the right air temperature actuator (3).
3. Remove the screws from the right air temperature actuator (3).
4. Remove the right air temperature actuator (3) from the HVAC module assembly (2).

Scheme 474

1. Install the right air temperature actuator (3) from the HVAC module assembly (2). NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the right air temperature actuator (3). Tighten Tighten the screws to 2 N.m (18 lb in).
3. Connect the electrical connector to the right air temperature actuator.
4. Install the I/P carrier. Refer to INSTRUMENT PANEL (I/P) CARRIER REPLACEMENT in Instrument Panel, Gages, and Console.
5. Reprogram the air temperature actuator. Refer to «RE-CALIBRATING ACTUATORS»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__re-calibrating-actuators) .

Scheme 475

1. Remove the I/P insulator panel. Refer to INSULATOR REPLACEMENT - INSTRUMENT PANEL (I/P) in Instrument Panel, Gages and Console.
2. Disconnect the electrical connector (1) from the left air temperature actuator (2).
3. Remove the screws from the left air temperature actuator (2).
4. Remove the left air temperature actuator (2) from the HVAC module assembly (3).

Scheme 476

1. Install the left air temperature actuator (2) to the HVAC module assembly (3). NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the left air temperature actuator (2). Tighten Tighten the screws to 2 N.m (18 lb ft).
3. Install the electrical connector (1) to the left air temperature actuator (2).
4. Install the I/P insulator panel. Refer to INSULATOR REPLACEMENT - INSTRUMENT PANEL (I/P) 1 in Instrument Panel, Gages, and Console.
5. Reprogram the left air temperature actuator. Refer to «RE-CALIBRATING ACTUATORS»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__re-calibrating-actuators) .

Scheme 477

Scheme 478

Scheme 479

1. Remove the floor air outlet duct extension (1) from the floor duct (2).
2. Disconnect the electrical connection at the mode actuator (10).
3. Remove the mode actuator mounting screws from the HVAC module.
4. Remove the mode actuator as an assembly with the actuator cam.

Scheme 480

Scheme 481

Scheme 482

1. Install the mode actuator as an assembly with the actuator cam. Line up the heater/defroster valve lever with the mode actuator cam slot. Line up the A/C valve lever with the mode actuator cam. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the mode actuator mounting screw to the HVAC module. Tighten Tighten the screw to 1.6 N.m (14 lb in).
3. Connect the electrical connection at the mode actuator (10).
4. Install the floor air outlet duct extension (1) to the floor air duct (2).

Scheme 483

Scheme 484

1. Remove the push pin (5) from the HVAC module (2).
2. Remove the left floor duct (1) from the HVAC module (2).
3. Disconnect the electrical connector (3) from the mode actuator (4).
4. Remove the screws from the mode actuator (4).
5. Remove the mode actuator (4) from the HVAC module (1).
6. Remove the cam (2) from the HVAC module (1).

Scheme 485

Scheme 486

1. Install the cam (2) to the HVAC module (1).
2. Install the mode actuator (4) to the HVAC module (1). NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
3. Install the screws to the mode actuator (4). Tighten Tighten the screws to 2 N.m (18 lb in).
4. Connect the electrical connector (3) to the mode actuator (4).
5. Install the left floor air outlet duct (1) to the HVAC module (2).
6. Install the push pin (5) to the HVAC module (2).
7. Reprogram the Right air temperature actuator. Refer to «RE-CALIBRATING ACTUATORS»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__re-calibrating-actuators) .

Scheme 487

Scheme 488

1. Remove the air distribution duct. Refer to AIR DISTRIBUTOR DUCT REPLACEMENT .
2. Disconnect the electrical connection from the recirculation actuator (1).
3. Remove the recirculation actuator retaining screws.
4. Remove the recirculation actuator.

Scheme 489

Scheme 490

1. Install the recirculation actuator. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the recirculation actuator retaining screws. Tighten Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector to the recirculation actuator (1).
4. Install the air distribution duct. Refer to AIR DISTRIBUTOR DUCT REPLACEMENT .

Scheme 491

Scheme 492

1. Remove the HVAC module assembly. Refer to HVAC MODULE ASSEMBLY REPLACEMENT .
2. Remove the screws from the evaporator core cover (1).
3. Remove the evaporator core cover (1) from the HVAC module assembly (2).
4. Remove the screws from the recirculation actuator (1).
5. Remove the recirculation actuator (1) from the HVAC module assembly (2).

Scheme 493

Scheme 494

1. Install the recirculation actuator (1) to the HVAC module assembly (2). NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the recirculation actuator (1). Tighten Tighten the screws to 2 N.m (18 lb in).
3. Install the evaporator core cover (1) to the HVAC module assembly (2).
4. Install the screws to the evaporator core cover (1). Tighten Tighten the screws to 2 N.m (18 lb in).
5. Install the HVAC module assembly. Refer to HVAC MODULE ASSEMBLY REPLACEMENT .
6. Reprogram the recirculation actuator. Refer to «RE-CALIBRATING ACTUATORS»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual__re-calibrating-actuators) .

Scheme 495

1. Remove the overhead console screw.
2. Remove the overhead console from the headliner.
3. Disconnect the electrical connectors from the auxiliary HVAC control assembly.
4. Remove the overhead console from the vehicle.
5. Remove the auxiliary HVAC control assembly from the overhead console.

Scheme 496

1. Install the auxiliary HVAC control assembly to the overhead console.
2. Connect the electrical connectors to the auxiliary HVAC control assembly.
3. Install the overhead console to the headliner. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the overhead console screw. Tighten Tighten the screw to 2 N.m (18 lb in).

Scheme 497

1. Remove the overhead console screw.
2. Remove the overhead console from the headliner.
3. Disconnect the electrical connectors from the auxiliary HVAC control module assembly.
4. Remove the overhead console from the vehicle.
5. Remove the auxiliary HVAC control assembly from the overhead console.

Scheme 498

1. Install the auxiliary HVAC control assembly to the overhead console.
2. Connect the electrical connectors to the auxiliary HVAC control module assembly.
3. Install the overhead console to the headliner. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
4. Install the overhead console screw. Tighten Tighten the screw to 2 N.m (18 lb in).

Scheme 499

1. Separate the front of the overhead console (1) from the headliner.
2. Push the assembly rearward and pull down in order to access the retaining tabs.
3. Remove the auxiliary HVAC control assembly (2) by releasing the tabs at the rear of the control and push out from the rear.
4. Disconnect the electrical connector (3).

Scheme 500

1. Connect the electrical connector (3).
2. Install the auxiliary HVAC control assembly (2) to the console (1).
3. Install the overhead console (1) to the headliner.

Scheme 501

Scheme 502

1. Remove the auxiliary rear HVAC control assembly. Refer to «HVAC CONTROL ASSEMBLY REPLACEMENT - REAR AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual) .
2. Remove the auxiliary HVAC control processor (2) from the bracket (3).
3. Remove the cover from the auxiliary HVAC control processor (2).
4. Remove the auxiliary HVAC control processor (2) from the box (1).

Scheme 503

Scheme 504

1. Install the auxiliary HVAC control processor (2) to the box. (1)
2. Install the cover to the auxiliary HVAC control processor (2).
3. Install the auxiliary HVAC control processor (2) to the bracket (3).
4. Install the auxiliary rear HVAC control assembly. Refer to «HVAC CONTROL ASSEMBLY REPLACEMENT - REAR AUXILIARY»(/cadillac/escalade/gmt800-2001-2006/remont/manual-hvac-system/#hvac-systems-manual) .

Scheme 505

1. Remove the console (1) from the headliner.
2. Remove the auxiliary blower motor switch (2) by releasing the tabs at the rear of the overhead console.
3. Disconnect the electrical connector (3).

Scheme 506

1. Connect the electrical connector (3).
2. Install the blower motor switch (2) to the overhead console.
3. Install the overhead console (1) to the headliner.

Scheme 507

1. Remove the right rear quarter trim panel. Refer to TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.
2. Disconnect the electrical connector from the auxiliary air temperature actuator.
3. Remove the retaining screws from the auxiliary air temperature actuator.
4. Remove the auxiliary air temperature actuator (1) from the rear auxiliary HVAC module.

Scheme 508

1. Install the auxiliary air temperature actuator (1) to the auxiliary HVAC module. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the auxiliary air temperature actuator retaining screws. Tighten Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector to the auxiliary air temperature actuator.
4. Install the right rear quarter trim panel. Refer toTRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.

Scheme 509

1. Remove the right rear quarter trim panel. Refer to TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.
2. Disconnect the electrical connector from the mode actuator (1).
3. Remove the retaining screws from the mode actuator.
4. Remove the mode actuator (1) from the vehicle.

Scheme 510

1. Install the mode actuator (1) to the vehicle. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the mode actuator (1). Tighten Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector to the mode actuator.
4. Install the left rear quarter trim panel. Refer to TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.

Scheme 511

1. Remove the right rear quarter trim panel. Refer to TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.
2. Disconnect the electrical connector from the mode actuator (1).
3. Remove the retaining screws from the mode actuator.
4. Remove the mode actuator (1) from the vehicle.

Scheme 512

1. Install the mode actuator (1) to the vehicle. NOTE: Refer to «FASTENER NOTICE»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the screws to the mode actuator (1). Tighten Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector to the mode actuator.
4. Install the right rear quarter trim panel. Refer to TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (UTILITY) or TRIM PANEL REPLACEMENT - REAR QUARTER - RIGHT (SUBURBAN) in Interior Trim.

Air Delivery Description and Operation

The air delivery description and operation is divided into six areas

1. HVAC Control Components
2. Air Speed
3. Auxiliary Air Speed
4. Air Delivery
5. Auxiliary Air Delivery
6. Recirculation Operation

HVAC Control Module

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features

Scheme 513

Auxiliary HVAC Control Processor

The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. It receives inputs from the front and rear auxiliary HVAC control assemblies. The processor positions the auxiliary air temperature actuator and auxiliary mode actuator based on these inputs. This processor does not have Class 2 communication available.

The auxiliary HVAC control processor receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through rear auxiliary HVAC control assembly and a splice pack. The system receives 12 volt varied voltage input for auxiliary air temperature change request. Then the processor creates a 12 volt varied output for control of the auxiliary air temperature actuator. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Front Auxiliary HVAC Control Assembly

The front auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the Aux.position is selected, inputs from this control assembly will not be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when Aux. is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Rear Auxiliary HVAC Control Assembly

The rear auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the rear headliner so that second row seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. When the Aux. position is selected, on the front HVAC control assembly, inputs from this control assembly will be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The rear auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when Aux. is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Mode Actuator

The mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Auxiliary Mode Actuator

The auxiliary mode actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear-ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the auxiliary HVAC control processor sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Air Speed - Front Control

The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series with the HVAC control module by the off blower motor control circuit.

Depending upon the selected speed, power is provided to the blower motor from either the ignition 3 voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.

Low Blower Speed

When the Low 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

Medium Blower Speeds

When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

High Blower Speed

When the High blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery positive voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.

Air Speed - Auxiliary

There are two separate control assemblies for the auxiliary HVAC system. There is the front auxiliary HVAC control assembly and the rear auxiliary HVAC control assembly. Both control assemblies provide input to the auxiliary HVAC control processor. If the front auxiliary HVAC control assembly is in any other position than OFF or REAR, the auxiliary HVAC control processor will only use inputs from the front HVAC controls. If the front auxiliary HVAC control assembly is in the Aux. position, then the system will only function with inputs from the rear auxiliary HVAC control assembly. If the front auxiliary HVAC control assembly is in the OFF position, then the auxiliary HVAC control processor does not respond to input from either control assembly. The auxiliary HVAC control processor can not request A/C compressor clutch engagement from the PCM. The rotary switches on the auxiliary HVAC control module and the front auxiliary HVAC control assembly provide the operator the ability to select several blower speeds.

Off Mode

When the OFF blower setting is selected on the front auxiliary HVAC control assembly, the switch creates an open circuit within the front auxiliary HVAC control assembly. This prevents any output being provided by either the front or rear auxiliary HVAC control assembly. If the OFF blower setting is selected on the rear auxiliary HVAC control assembly, the switch will create an open within the rear auxiliary HVAC control assembly. This prevents any output being provided to the auxiliary blower motor, as long as the front auxiliary HVAC control assembly is in the OFF position. The front auxiliary HVAC control assembly controls the rear auxiliary HVAC control assembly on the auxiliary blower motor switch control circuit.

Auxiliary Low Blower Speed

When the Low blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary low speed blower motor relay through the auxiliary blower motor low speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 2 series resistors in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the Low blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary low speed blower motor relay through the auxiliary blower motor low speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the Aux. CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary low speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 2 series resistors in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

Auxiliary Medium Blower Speed

When the Medium blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary medium speed blower motor relay through the auxiliary blower motor medium speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 1 series resistor in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the Medium blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary medium speed blower motor relay through the auxiliary blower motor medium speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the Aux. CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary medium speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 1 series resistor in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

Auxiliary High Blower Speed

When the High blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary high speed blower motor relay through the auxiliary blower motor high speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is sent directly to the auxiliary blower motor by the auxiliary blower motor supply voltage circuit. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the High blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary high speed blower motor relay through the auxiliary blower motor high speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the Aux. CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary high speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is sent directly to the auxiliary blower motor by the auxiliary blower motor supply voltage circuit. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

Air Distribution

The HVAC control module controls the distribution of air by the use of a defrost actuator and a mode actuator. The modes that may be selected are

1. Defrost
2. Defog
3. Panel
4. Bl-Level
5. Floor

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control module sends signals to the mode door actuator through the mode door control circuit. Zero volts drives the actuator in one direction while 5-volts moves the actuator in the opposite direction. When the actuator receives 2.5-volts, the actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control module's software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position.

Front Defrost

When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3°C (38°F). The blower motor will be activated, regardless of the coolant temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.

Air Distribution - Auxiliary Control

The auxiliary HVAC system provides ventilation for the rear seat occupants. The rear seat occupants will exercise control of the auxiliary air delivery modes, air speed and the air temperature setting. The front auxiliary HVAC control assembly will have the ability to override the rear auxiliary HVAC control module by placing it in any position other than Aux.

The auxiliary mode switch in the front auxiliary HVAC control assembly allows the driver to direct the air flow in the rear of the vehicle between the floor, headliner, or a blend between the two options. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary mode actuator from the IP fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the mode switch, a varied voltage is sent to the auxiliary mode actuator on the auxiliary mode door control circuit, and auxiliary HVAC control processor. The auxiliary mode actuator moves the mode door to the desired output. Ground for the auxiliary mode actuator, auxiliary HVAC control processor and front auxiliary HVAC control assembly are provided by the ground circuit.

Recirculation Operation

The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.

Air Temperature Description and Operation

The air temperature controls are divided into five areas

1. HVAC Control Components
2. Heating and A/C Operation
3. Auxiliary Heating and A/C Operation
4. Engine Coolant
5. A/C Cycle

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features

Scheme 514

The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. It receives inputs from the front and rear auxiliary HVAC control assemblies. The processor positions the auxiliary air temperature actuator and auxiliary mode actuator based on these inputs. This processor does not have Class 2 communication available.

The auxiliary HVAC control processor receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through rear auxiliary HVAC control assembly and a splice pack. The system receives 12 volt varied voltage input for auxiliary air temperature change request. Then the processor creates a 12 volt varied output for control of the auxiliary air temperature actuator. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

The front auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the AUX position is selected, inputs from this control assembly will not be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when AUX is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

The rear auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the rear headliner so that second row seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. When the AUX position is selected, on the front HVAC control assembly, inputs from this control assembly will be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The rear auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when AUX is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Air Temperature Actuator

The air temperature actuators are a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Auxiliary Air Temperature Actuator

The auxiliary air temperature actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear-ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the auxiliary HVAC control processor sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3 wire piezoelectric pressure transducer. A 5 volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The PCM converts the voltage signal to a pressure value.

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables the compressor clutch if the A/C pressure is more than 2957 kPa (429 psi). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi).

A/C Low Pressure Switch

The A/C low pressure switch protects the A/C system from a low pressure condition that could damage the A/C compressor or cause evaporator icing. The HVAC control module applies 12 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 124 kPa (18 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40 psi). This enables the A/C compressor to turn back ON.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature

1. Recirculation actuator setting
2. Difference between inside and desired temperature
3. Difference between ambient and desired temperature
4. Blower motor speed setting
5. Mode setting
6. Auxiliary HVAC settings

The manual HVAC system is a dual temperature zone system. There are two separate air temperature levers. Moving the air temperature levers to the upward position diverts most of the airflow through the heater core, which increases the outlet air temperature. Moving the air temperature levers to the most downward position diverts most of the airflow around the heater core, which decreases the outlet air temperature. The air temperature offset can be as much as 16.7°C (30°F).

Pressing the A/C button enables the HVAC control module to request A/C compressor engagement and turn on the A/C button LED. The HVAC control module sends a class 2 message to the PCM for A/C compressor engagement. The PCM will provide a ground for the A/C compressor relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch coil. The A/C compressor diode will prevent a voltage spike, resulting from the collapse of the magnetic field of the coil, from entering the vehicle electrical system when the compressor is disengaged. Defrost and Defog mode selections will request A/C operation but not turn on the A/C LED.

The following conditions must be met in order for the A/C compressor clutch to turn on

1. Ambient air temperature above 4°C (40°F)
2. A/C low pressure switch signal circuit is grounded
3. A/C refrigerant pressure sensor parameter is less than 2957 kPa (429 psi)
4. PCM receives an A/C request from the HVAC control module
5. Engine coolant temperature (ECT) is less than 121°C (250°F)
6. The engine RPM is more than 550 RPM
7. The throttle position is less than 100%

The HVAC control module monitors the A/C low pressure switch signal circuit. If the voltage signal on this circuit has no voltage drop the module will interpret this condition as a low pressure, disabling the A/C request. The A/C low pressure switch will open its internal contacts at 151 kPa (22 psi). Then close the contacts at 275 kPa (40 psi) to resume A/C operation. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level.

The PCM monitors the A/C refrigerant pressure sensor signal circuit. The voltage signal on this circuit is proportional to the refrigerant pressure inside the A/C high side pressure line. As the pressure inside the line increases, so does the voltage signal. If the pressure is above 2957 kPa (429 psi), the A/C compressor output is disabled. When the pressure lowers to 1578 kPa (229 psi), the PCM enables the compressor to operate.

The sensor information is used by the PCM to determine the following

1. The A/C high side pressure
2. An A/C system load on the engine
3. An excessive A/C high side pressure
4. The heat load at the A/C condenser

Once engaged, the compressor clutch will be disengaged for the following conditions

1. Ambient air temperature is less than 4°C (40°F)
2. Throttle position is 100%
3. The A/C low pressure switch is open
4. A/C high side pressure is more than 2957 kPa (429 psi)
5. A/C low side pressure is less than 151 kPa (22 psi)
6. Engine coolant temperature (ECT) is more than 121°C (250°F)
7. Engine speed is more than 5500 RPM
8. Transmission shift
9. PCM detects excessive torque load
10. PCM detects insufficient idle quality
11. PCM detects a hard launch condition

Auxiliary Heating and A/C Operation

There are two separate control assemblies for the auxiliary HVAC system. There is the front auxiliary HVAC control assembly and the rear auxiliary HVAC control assembly. Both control assemblies provide input to the auxiliary HVAC control processor. If the front auxiliary HVAC control assembly is in any other position than OFF or AUX, the auxiliary HVAC control processor will only use inputs from the front HVAC controls. If the front auxiliary HVAC control assembly is in the AUX position, then the system will only function with inputs from the rear auxiliary HVAC control assembly. If the front auxiliary HVAC control assembly is in the OFF position, then the auxiliary HVAC control processor does not respond to input from either control assembly. The auxiliary HVAC control processor can not request A/C compressor clutch engagement from the PCM.

The auxiliary air temperature switch is a rotary knob switch. Turning the air temperature switch to the warmest position diverts most of the airflow through the heater core, which increases the outlet air temperature. Turning the air temperature switch to the coolest position diverts most of the airflow around the heater core, which decreases the outlet air temperature.

Engine Coolant

Engine coolant is the essential element of the heating system. The thermostat controls the normal engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation.

Coolant enters the heater core through the inlet heater hose, in a pressurized state. The heater core is located inside the HVAC module. The ambient air drawn through the HVAC module absorbs the heat of the coolant flowing through the heater core. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. Opening or closing the air temperature door controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

A/C Cycle

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system. The A/C system is mechanically protected with the use of a high pressure relief valve. If the A/C refrigerant pressure sensor were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line, to the orifice tube.

The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to vaporize at the orifice tube. The orifice tube also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the orifice tube flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the compressor, in a vapor state, and completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment will also change form, or condense, and is discharged from the HVAC module as water.

A/C Cycle with Auxiliary

The auxiliary A/C system operates from the vehicles primary A/C system. The front or primary A/C system must be ON to allow the rear A/C system to function.

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C system used on this vehicle is a non cycling system. Non cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal, to the compressor clutch, in the event that the refrigerant pressure becomes excessive. After the high and low side of the A/C system pressure equalize, the high pressure switch will CLOSE. Closing the high pressure switch will complete the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line. The liquid line flow is split and the liquid refrigerant flows to both the front or primary A/C system, and to the liquid line for the rear A/C system.

The liquid refrigerant, flowing to the rear A/C system, flows into the rear TXV. The rear TXV is located at the rear evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the rear A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to boil at the expansion device. The TXV also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the rear A/C module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs the moisture and heat from the ambient air. The refrigerant exits the evaporator through the suction line and back to the primary A/C systems suction line. Refrigerant in the primary A/C system suction line flows back to the compressor, in a vapor state, and completes the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the rear A/C module for passenger comfort. The heat and moisture removed from the rear passenger compartment will also change form, or condense, and is discharged from the rear A/C module as water.

Scheme 515

See also:
• FASTENER NOTICE
• AIR DELIVERY DESCRIPTION AND OPERATION
• AIR TEMPERATURE DESCRIPTION AND OPERATION
• HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE
• RE-CALIBRATING ACTUATORS