HVAC Systems - Automatic Cadillac XLR I

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table (Air Temperature Duct Sensor)

Sensor Resistance Table (Air Temperature Duct Sensor)

Sensor Resistance Table (Inside and Ambient Air Temp Sensor)

Sensor Resistance Table (Inside and Ambient Air Temp Sensor)

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Scheme 15

Scheme 16

Scheme 17

HVAC Connector End Views

A/C Compressor Clutch

Scheme 18

HVAC Connector End Views

A/C Refrigerant Pressure Sensor

Scheme 19

HVAC Connector End Views

Air Temperature Actuator - Left

Air Temperature Actuator - Right

HVAC Connector End Views

Air Temperature Actuator - Right

Scheme 20

HVAC Connector End Views

Air Temperature Sensor - Inside

Scheme 21

HVAC Connector End Views

Air Temperature Sensor - Lower Left

Air Temperature Sensor - Lower Right

HVAC Connector End Views

Air Temperature Sensor - Lower Right

Air Temperature Sensor - Upper Left

HVAC Connector End Views

Air Temperature Sensor - Upper Left

Air Temperature Sensor - Upper Right

HVAC Connector End Views

Air Temperature Sensor - Upper Right

Scheme 22

HVAC Connector End Views

Ambient Air Temperature Sensor

Scheme 23

HVAC Connector End Views

Blower Motor Control Processor

Scheme 24

HVAC Connector End Views

HVAC Control Module C1

Scheme 25

HVAC Connector End Views

HVAC Control Module C2

Scheme 26

HVAC Connector End Views

HVAC Control Module C3

Scheme 27

HVAC Connector End Views

Mode Actuator

Recirculation Actuator

HVAC Connector End Views

Recirculation Actuator

Scheme 28

HVAC Connector End Views

Sunload Sensor Assembly

Scheme 29

HVAC Connector End Views

Vacuum Bypass Valve Solenoid

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

IPC Scan Tool Output Controls

ECM Scan Tool Output Controls

Scan Tool Data List

Use the Scan Tool Data Display Values and Definitions Information in order to assist in diagnosing the HVAC control module concerns. Compare the vehicles actual scan tool data with the typical data display value table information. Use the data information in order to aid in understanding the nature of the concern when the vehicle does not match with the typical data display values.

The scan tool data values were taken from a known good vehicle under the following conditions

1. The ignition switch is in the ON position.
2. The engine is running at idle.
3. The vehicle is in PARK.
4. The doors are closed.
5. The windows are closed.
6. The A/C is ON.
7. The ambient air temperatures are at 22-27°C (70-80°F).

Heating and Air Conditioning Scan Tool Data List

ECM Scan Tool Data List

Vehicle Control Systems ECU Identification Information - HVAC

Circuit Description

The ambient air temperature sensor allows the HVAC control module to monitor the temperature of the air surrounding the front of the vehicle. The inside air temperature sensor assembly allows the HVAC control module to monitor the temperature of the air inside the passenger compartment. The inside air temperature assembly contains an electric fan which pulls the air from the passenger compartment to the sensor. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuits. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. The HVAC control module also uses the ambient air temperature input to calculate the value of the ambient air temperature display. When the air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistances of the sensors are low and the voltage signals are low.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0159 Outside Air Temperature Sensor Circuit
2. DTC B0164 Passenger Compartment Temperature Sensor Circuit

Conditions for Running the DTC

1. Battery voltage to the HVAC control module is greater than 8.7 volts and less than 16.5 volts.
2. The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control module determines that the voltage applied to the input for the air temperature sensor is less than -40 to +215°C (-40 to +419°F).

Action Taken When the DTC Sets

1. The driver information center (DIC) will display a default value of 75 in place of the ambient air temp sensor.
2. The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

Conditions for Clearing the DTC

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.

Test Description

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

1. 2: Verifies that the temperature displayed is not within the calibrated range.
2. 3: Tests for the proper operation of the circuit in the high voltage range.
3. 4: Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC B0159 or B0164

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 volt is approximately equal to 51 counts.

1. Output Air Temperature Sensor 1 refers to the upper left air temperature sensor
2. Output Air Temperature Sensor 2 refers to the lower left air temperature sensor
3. Output Air Temperature Sensor 3 refers to the upper right air temperature sensor
4. Output Air Temperature Sensor 4 refers to the lower right air temperature sensor

This diagnostic procedure supports the following DTCs

1. DTC B0174 Output Air Temperature Sensor 1
2. DTC B0179 Output Air Temperature Sensor 2
3. DTC B0510 Output Air Temperature Sensor 3
4. DTC B0515 Output Air Temperature Sensor 4

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

The HVAC control module detects the signal circuit is less than 5 counts (0.09 volt) or greater than 250 counts (4.90 volts).

The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

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

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

1. 2: Verifies that the temperature displayed is not within the calibrated range.
2. 3: Tests for the proper operation of the circuit in the high voltage range.
3. 4: Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC B0174, B0179, B0510, or B0515

The HVAC control module monitors the ambient light on the left and right side of the vehicle through a light sensitive photo diode called a sunload sensor assembly. The HVAC control module uses this information to compensate for the effect of the sun on the inside air temperature of the vehicle. When the sensor is in direct sunlight, the signal voltage is low. When the sensor is shaded, the signal voltage is high. The HVAC control module requests A/C compressor clutch engagement and controls the air temperature actuator door positions in order to maintain the selected air temperature on the HVAC control module.

This diagnostic procedure supports the following DTCs

1. DTC B0184 Solar Load Sensor Left
2. DTC B0189 Solar Load Sensor Right

The ignition is turned ON.

The HVAC control module detects the signal circuit is less than 5 counts (0.09 volts) or greater than 250 counts (4.90 volts).

The HVAC control module uses a default sunload sensor value for further automatic control calculations. The default values are not displayed on the scan tool.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

If condition not present refer to Testing for Intermittent Conditions and Poor Connections .

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

1. 2: Verifies that the temperature displayed is not within the calibrated range.
2. 3: Tests for the proper operation of the circuit in the high voltage range.
3. 4: Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC B0184 or B0189

The actuator is an electronic stepper motor. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value 0 volts. The HVAC control module determines the door or mode film position by counting pulses, voltage fluctuations, caused by the brush to commutator action generated during normal motor operation. The HVAC control module monitors a voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts.

When a calibration or recalibration procedure is performed, the HVAC control module calculates the door or mode film travel range. The HVAC control module commands the actuator in one extreme position then counts pulses starting from 0 counts. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.

1. Air Flow Control 3 Circuit refers to the mode actuator
2. Air Flow Control 7 Circuit refers to the recirculation actuator
3. Temperature Control 1 Circuit refers to the left air temperature
4. Temperature Control 2 Circuit refers to the right air temperature

This diagnostic procedure supports the following DTCs

1. DTC B0248 Air Flow Control 3 Circuit
2. DTC B0268 Air Flow Control 7 Circuit
3. DTC B0408 Temperature Control 1 Circuit
4. DTC B0423 Temperature Control 2 Circuit

The ignition is turned ON. The inoperative actuator DTC runs during and after the next range check following the setting of the actuator range error DTC. The appropriate actuator inoperative code will set with the appropriate actuator range error code.

1. DTC B0249 Air Flow Control 3 Circuit Range
2. DTC B0269 Air Flow Control 7 Circuit Range
3. DTC B0409 Temperature Control 1 Circuit Range
4. DTC B0419 Temperature Control 2 Circuit Range

The HVAC control module does not detect any movement of the actuator.

1. The HVAC control module will recalibrate the appropriate actuator each time the ignition switch is turned ON.
2. If DTC B0268 is set, the HVAC control module will command the recirculation door to the outside air position.

Conditions for Clearing the MIL/DTC

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

1. Inspect the actuator door and actuator for the following conditions: A misaligned actuator-Refer to «Mode Actuator Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Right Side»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Left Side»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) or «Recirculation Actuator Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) . Broken or binding mode actuator film or actuator door Obstruction that prevents the mode film or actuator door from operating within its full range of motion Missing seals to the actuator door Misaligned seals to the actuator door
2. Refer to «Testing for Intermittent Conditions and Poor Connections»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__testing-for-intermittent-conditions-and-poor) .

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

1. 2: This step verifies that the HVAC control module is able to command the appropriate actuator through its full range of motion.
2. 4: If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, the actuator, or the wiring harness. If the actuator does move, but not within its full range of motion, the problem is likely to be a mechanical binding of the actuator door or actuator door linkage.
3. 6: This step drives the actuator in one position. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.
4. 7: This step drives the actuator in the opposite direction.

DTC B0248, B0268, B0408, or B0423

The actuator is an electronic stepper motor. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value 0 volts. The HVAC control module determines the door or mode film position by counting pulses (voltage fluctuations) caused by the brush to commutator action generated during normal motor operation. The HVAC control module monitors a voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts.

When a calibration or recalibration procedure is performed, the HVAC control module calculates the door or mode film travel range. The HVAC control module commands the actuator in one extreme position then counts pulses starting from 0 counts. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.

1. Air Flow Control 3 Circuit refers to the mode actuator
2. Air Flow Control 7 Circuit refers to the recirculation actuator
3. Temperature Control 1 Circuit refers to the left air temperature actuator
4. Temperature Control 2 Circuit refers to the right air temperature actuator

This diagnostic procedure supports the following DTCs

1. DTC B0249 Air Flow Control 3 Circuit Range
2. DTC B0269 Air Flow Control 7 Circuit Range
3. DTC B0409 Temperature Control 1 Circuit Range
4. DTC B0419 Temperature Control 2 Circuit Range

The HVAC control module will run the DTC when either of the following conditions are met.

1. The HVAC control module has completed a calibration/recalibration of the actuator.
2. The HVAC control module commands the actuator to move.

The HVAC control module will set this DTC if either of the following conditions are true.

1. The actuator fails calibration/recalibration due to an over travel or under travel condition. The HVAC control module does not detect the calibrated number of total pulse counts during a travel range check.
2. The HVAC control module determines that the actual door position does not equal the commanded door position. The HVAC control module commands the door to move but does not see the expected number of pulses between positions.

1. The HVAC control module will attempt to make use of whatever range is still available.
2. The HVAC control module will recalibrate the actuator each time the ignition switch is turned ON.

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

1. Inspect the appropriate actuator door and actuator for the following conditions: A misaligned actuator-Refer to «Mode Actuator Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Right Side»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) , «Air Temperature Actuator Replacement - Left Side»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) or «Recirculation Actuator Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) . Broken or binding mode actuator film or actuator door Obstruction that prevents the mode film or actuator door from operating within its full range of motion Missing seals to the actuator door Misaligned seals to the actuator door
2. Refer to «Testing for Intermittent Conditions and Poor Connections»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__testing-for-intermittent-conditions-and-poor) .

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

1. 2: This step verifies that the HVAC control module is able to command the actuator through its full range of motion.
2. 4: If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, the actuator, or the wiring harness. If the actuator does move, but not within its full range of motion, the problem is likely to be a mechanical binding of the actuator door or actuator door linkage.
3. 6: This step drives the actuator in one direction. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.
4. 7: This step drives the actuator in the opposite direction.

DTC B0249, B0269, B0409, or B0419

The engine control module (ECM) monitors the high side refrigerant pressure through an air conditioning (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 the pressure is high, the ECM commands the cooling fans ON. When the pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

This diagnostic procedure supports the following DTCs

1. DTC P0531 A/C Refrigerant Pressure Sensor Performance
2. DTC P0532 A/C Refrigerant Pressure Sensor Circuit Low Voltage
3. DTC P0533 A/C Refrigerant Pressure Sensor Circuit High Voltage

1. The engine is running.
2. A/C OFF when P0531 is set.

P0531

The ECM detects the A/C pressure signal circuit is more than 4.5 volts for 4 minutes.

The ECM detects an A/C pressure of less than 0.1 volt for 1.6 seconds.

P0533

The ECM detects an A/C pressure of more than 4.9 volts for 1.6 seconds.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM stores the failure records.
3. The A/C compressor clutch is disabled.
4. SERVICE A/C SYSTEM displays on the driver information center (DIC).
5. A/C OFF displays on the HVAC control module.
6. The A/C compressor clutch will not be disabled if only DTC P0531 is set.

1. The ECM will not store failure records if only DTC P0531 is set.
2. The DTC will become history if the ECM no longer detects a failure.
3. The history DTC will clear after 40 fault-free ignition cycles.
4. Clear the DTC with a scan tool then cycle the ignition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .

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

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.

DTC P0531, P0532, or P0533

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

This diagnostic procedure supports the following DTCs

1. DTC P0645 A/C Clutch Relay Control Circuit
2. DTC P0646 A/C Clutch Relay Control Circuit Low Voltage.
3. DTC P0647 A/C Clutch Relay Control Circuit High Voltage.

1. The ignition must be ON and the voltage must be between 9-18 volts.
2. The ECM driver is activated or deactivated.

1. The ECM detects an improper voltage level on the output circuit that controls the A/C relay.
2. The condition is present for at least 5 seconds.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM will not store Freeze Frame or Failure Records.
3. The A/C compressor clutch is disabled for the ignition cycle.

1. The DTC will become history if the ECM 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.

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

1. 2: Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3: Tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
3. 4: Verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
4. 8: Tests for a short to voltage or an open.
5. 10: If the A/C fuse is open ensure to test the A/C compressor clutch supply voltage circuit for short to ground.

DTC P0645, P0646, or P0647

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/xlr/i-2003-2009/remont/oem-general-information/#vehicle-dtc-information) in Vehicle DTC Information before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to the following information: «Air Delivery Description and Operation»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__air-delivery-description-and-operation) «Air Temperature Description and Operation»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__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»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__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. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__air-temperature-description-and-operation) .
6. 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
7. 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 Conditions 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/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__hvac-compressor-clutch-does-not-engage)
2. «HVAC Compressor Clutch Does Not Disengage»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__hvac-compressor-clutch-does-not-disengage)
3. «Blower Motor Always On»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__blower-motor-always-on)
4. «Blower Motor Inoperative»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic__blower-motor-malfunction)
6. «Too Hot in Vehicle»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
7. «Too Cold in Vehicle»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
8. «Air Delivery Improper»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
9. «Air Recirculation Malfunction»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic)
10. «Leak Testing»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__leak-testing) in Heating, Ventilation and Air Conditioning
11. «Noise Diagnosis - Blower Motor»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor) in Heating, Ventilation and Air Conditioning
12. «Noise Diagnosis - Air Conditioning (A/C) System»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac) in Heating, Ventilation and Air Conditioning
13. «Odor Diagnosis»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis) in Heating, Ventilation and Air Conditioning

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Disengage

HVAC Compressor Clutch Does Not Disengage

Blower Motor Always On

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

Blower Motor Malfunction

Blower Motor Malfunction

1. 2: This test resets HVAC control module and checks for current air temperature actuator DTC.
2. 7: Ambient air temperature must be above 3°C (38°F) in order for this A/C Compressor test to be run.

Too Hot in Vehicle

1. 2: This test resets HVAC control module and checks for current air temperature actuator DTC.
2. 8: This checks for proper operation of coolant system to insure heater output.

Too Cold in Vehicle

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

1. 9: The Scan Tool should match the following specified values. Defrost-44 Counts Mix-Blend-66 Counts Floor-103 Counts Bi-Level-143 Counts Vent-255 Counts

Air Delivery Improper

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

1. 2: This action will calibrate the HVAC actuators and check to ensure the DTCs that set when calibration is performed will be set.
2. 4: This step is to ensure that the recirculation actuator is with its calibrated range.

Air Recirculation Malfunction

Afterblow Enabling

The afterblow mode can be enabled using the scan tool. The afterblow mode allows the blower motor to operate after the engine has been turned OFF. This operation of the blower motor dries the evaporator core, which reduces the amount of microbial growth which can create undesirable odors.

Use the following procedure in order to enable the afterblow mode

1. Connect the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Select HVAC Module.
4. Select HVAC Systems Automatic.
5. Select Special Functions.
6. Select HVAC.
7. Select Afterblow Option.
8. Select ENTER to enable the afterblow.
9. When done, use the soft key to save changes.

When afterblow has been enabled by the scan tool the blower motor will operate between medium and high speed for 4 minutes after the engine has been turned OFF.

The following conditions must be met for the HVAC module to operate the afterblow

1. The outside air temperature must be at least 21°C (70°F).
2. The A/C compressor must operate for more than 2 minutes.
3. The engine must be turned off for at least 45 minutes.
4. The system voltage must be at least 12 volts.

Calibration Procedure with a Scan Tool

Use the following steps to perform the calibration update

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, select HVAC Systems Automatic.
4. Select Special Functions.
5. Select HVAC.
6. Select Calibrate HVAC Module.
7. Select ON, wait 30 seconds.

Calibration Procedure without a Scan Tool

1. Turn OFF the ignition.
2. Remove the battery positive voltage circuit fuse of the HVAC control module.
3. Wait 60 seconds.
4. Install the fuse.

Removal Procedure

1. Disconnect the battery. Refer to «Battery Negative Cable Disconnection and Connection»(/cadillac/xlr/i-2003-2009/remont/charging-system/#battery-charging-system-and-starting-system) .
2. Remove the I/P accessory trim plate. Refer to «Instrument Panel Accessory Trim Plate Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) .
3. Remove the HVAC control module retaining screws.
4. Remove the HVAC control module.

Installation Procedure

1. Install the HVAC control module to the I/P trim plate.
2. Install the HVAC control module retaining screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connectors to the HVAC control module.
4. Install the I/P accessory trim plate. Refer to «Instrument Panel Accessory Trim Plate Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) .
5. Connect the battery. Refer to «Battery Negative Cable Disconnection and Connection»(/cadillac/xlr/i-2003-2009/remont/charging-system/#battery-charging-system-and-starting-system) .
6. Start and allow the engine to run for at least one minute.
7. Refer to «Control Module References»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__control-module-references) for programming and setup information.

1. Disconnect the battery. Refer to «Battery Negative Cable Disconnection and Connection»(/cadillac/xlr/i-2003-2009/remont/charging-system/#battery-charging-system-and-starting-system) in Engine Electrical.
2. Remove the RH lower insulator panel. Refer to «Instrument Panel Insulator Panel Replacement - Right Side»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
3. Disconnect the HVAC module wiring harness from the recirculation housing wire harness retainer.
4. Remove the recirculation actuator mounting screws.
5. Remove the recirculation actuator.
6. Disconnect the electrical connector from the recirculation actuator.

1. Connect the recirculation actuator electrical connector.
2. Install the recirculation actuator. Install the recirculation actuator mounting screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the HVAC module wiring harness to the recirculation housing wire harness retainer.
4. Install the RH lower insulator panel. Refer to «Instrument Panel Insulator Panel Replacement - Right Side»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
5. Connect the battery. Refer to «Battery Negative Cable Disconnection and Connection»(/cadillac/xlr/i-2003-2009/remont/charging-system/#battery-charging-system-and-starting-system) in Engine Electrical.

1. Remove the SIR bracket. Refer to «Instrument Panel Inflatable Restraint Module Bracket Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the mode actuator electrical connector.
3. Remove the mode actuator mounting screws.
4. Remove the mode actuator.

1. Install the mode actuator.
2. Install the mode actuator mounting screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the mode actuator electrical connector.
4. Install the SIR bracket. Refer to «Instrument Panel Inflatable Restraint Module Bracket Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
5. Recalibrate the actuators. Refer to «Actuator Recalibration»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) .

1. Remove the SIR bracket. Refer to «Instrument Panel Inflatable Restraint Module Bracket Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the RH air temperature actuator electrical connector.
3. Remove the RH air temperature actuator mounting screws.
4. Remove the RH air temperature actuator.

1. Install the RH air temperature actuator.
2. Install the RH air temperature actuator mounting screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the RH air temperature actuator electrical connector.
4. Install the SIR bracket. Refer to «Instrument Panel Inflatable Restraint Module Bracket Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
5. Recalibrate the actuators. Refer to «Actuator Recalibration»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) .

1. Remove the I/P assembly. Refer to «Instrument Panel Carrier Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the electrical connector from the left air temperature actuator.
3. Remove the actuator mounting screws.
4. Remove the actuator.

1. Install the left air temperature actuator.
2. Install the actuator mounting screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the actuator electrical connector.
4. Install the I/P assembly. Refer to «Instrument Panel Carrier Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
5. Recalibrate the actuators. Refer to «Actuator Recalibration»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#hvac-systems-automatic) .

1. Remove the I/P trim pad. Refer to «Instrument Panel Trim Pad Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the upper right DTM sensor electrical connector.
3. Remove the upper right DTM sensor from the air distribution duct.

1. Install the upper right DTM sensor to the air distribution duct.
2. Connect the upper right DTM sensor electrical connector.
3. Install the I/P trim pad. Refer to «Instrument Panel Trim Pad Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.

1. Remove the I/P cluster. Refer to «Instrument Cluster Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) .
2. Disconnect the upper left DTM sensor electrical connector.
3. Remove the upper left DTM sensor from the air distribution duct.

1. Install the upper left DTM sensor to the air distribution duct.
2. Connect the upper left DTM sensor electrical connector.
3. Install the I/P cluster. Refer to «Instrument Cluster Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) .

1. Remove the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect the lower LH DTM sensor electrical connector.
3. Remove the lower LH DTM sensor from the HVAC module.

1. Install the lower LH DTM sensor to the HVAC module.
2. Connect the lower LH DTM sensor electrical connector.
3. Install the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

1. Remove the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect the lower RH DTM sensor electrical connector.
3. Remove the lower RH DTM sensor from the HVAC module.

1. Install the lower RH DTM sensor to the HVAC module.
2. Connect the lower RH DTM sensor electrical connector.
3. Install the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/xlr/i-2003-2009/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

1. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/cadillac/xlr/i-2003-2009/remont/hoistjack/#general-information__lifting-and-jacking-the-vehicle) .
2. Disconnect the ambient air temperature sensor electrical connector.
3. Remove the push-in retainer securing the ambient air temperature sensor to the lower RH side of the radiator support.
4. Remove the ambient air temperature sensor from the radiator support (1).

1. Install the ambient air temperature sensor to the lower radiator support (1).
2. Install the push-in retainer to secure the ambient air temperature sensor to the radiator support.
3. Connect the ambient air temperature sensor electrical connector.

1. Remove the knee bolster. Refer to «Driver Knee Bolster Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
2. Remove the driver information center retaining screw.
3. Disconnect the driver information center from the I/P.
4. Disconnect the inside air temperature sensor from the driver information center bezel.
5. Disconnect the inside air temperature sensor electrical connector.

1. Connect the inside air temperature sensor electrical connector.
2. Install the inside air temperature sensor.
3. Connect the driver information center to the I/P.
4. Install the driver information center retaining screw. Tighten: Tighten the screw to 1.9 N.m (17 lb in).
5. Install the knee bolster. Refer to «Driver Knee Bolster Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.

1. Partially remove the I/P trim pad. Refer to «Instrument Panel Trim Pad Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages, and Console.
2. Gently lift the I/P trim pad to access the sun load sensor.
3. Rotate the sunload sensor to release from the I/P trim pad.
4. Disconnect the sunload sensor electrical connector.
5. Remove the sun load sensor from the vehicle.

1. Install the sun load sensor to the vehicle.
2. Connect the sun load sensor electrical connector.
3. Rotate to secure the sun load sensor to the I/P trim pad.
4. Install the I/P trim pad. Refer to «Instrument Panel Trim Pad Replacement»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages, and Console.

Air Delivery Description and Operation

The air delivery controls are divided into two primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

Air Speed

The blower motor forces air throughout the vehicles interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode. The blower motor will always operate at some speed as long as the HVAC control module is in any 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.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the under hood electrical center through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

When any blower speed is selected, whether manual or automatic, the blower motor control processor will control blower motor speeds based on a 5 volt signal circuit that is pulse width modulated (PWM) signal by the HVAC control module. When a low blower speed is requested, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. The blower motor control processor interprets the PWM signal and varies the ground on the blower motor control circuit internally. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. Toggling the blower button manually also activates the LCD display for the blower speed selected.

Off Mode

When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC module and out through the floor outlets. The HVAC control module attempts to match the inside air temperature and driver selected temperatures. Since the A/C compressor is not running, the incoming air may be warmed but not cooled. Press the driver side air temperature switch to turn off the HVAC system. The ambient air temperature will show on the display.

Recirculation Mode

When the recirculation switch is pressed, the HVAC control module will apply a ground to one of the recirculation door control circuits in order to obtain the desired position. The recirculation actuator is a reverse polarity motor, each circuit provides both power and ground to the recirculation actuator. When the actuator is being held in a stationary position, both of the recirculation door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a recirculate position is requested, one of the recirculation door control circuits will ground driving the recirculation actuator into the desired position. When an outside air position is requested, the other recirculation door control circuit will ground. This moves the recirculation actuator into an outside air position. This brings air from outside the vehicle instead of air from the inside.

The HVAC control module provides power and ground to the recirculation actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The recirculation mode can be used in both automatic and manual operation. The only time recirculation is not available is when FRONT DEFROST and mix blend mode is selected. The RECIRC LED will flash to alert the driver that recirculation mode is not available. Pressing the recirculation switch, from the OFF position, will set the blower, mode and A/C compressor clutch into automatic mode.

When in automatic mode, recirculation will stay on until either the vehicle operator selects outside air, by pressing the RECIRCULATION switch, or the HVAC control module automatically moves the recirculation actuator. Automatic recirculation is only available when air temperatures are 21°C (70°F) or warmer. The recirculation actuator position will vary to obtain a cooler duct air temperature when cool air is selected. This will assist in cooling the vehicle quicker.

The HVAC control module will move the recirculation actuator to the outside air position at ignition off to bring fresh air to replace stale air that has accumulated in the HVAC module during shut down.

When requested the recirculation actuator will be able to move to the 100% recirculation position for a limited time, after that limited time the actuator will move to the 90% position. In the auto mode only, the recirculation actuator will move faster to the recirculation position when vehicle is at an idle compared to the normal speed of the actuator during normal operation.

If the recirculation actuator or related circuits has a failure the HVAC control module will attempt to drive the actuator to the outside air position regardless of mode selection. If there is a failure with one of the air temperature actuators the HVAC control module will allow the recirculation actuator to move to the outside air position.

Automatic Modes

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For fully automatic operation, both the blower and mode buttons must be in the AUTO position. Blower speeds will change automatically based on inputs to the HVAC control module. The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN. Only RECIRCULATION will have to be reset after each ignition cycle.

Moisture tends to accumulate in the HVAC module assembly after the engine has been shut off. The HVAC control module will purge the HVAC module of stale air and moisture to prevent window fogging. The mode actuator will move to the floor mode and run the low speed blower for 10 seconds to purge out the air and moisture. The recirculation actuator will be in the outside air position. Purge mode can be bypassed if any manual modes are selected.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, when temperatures are -1°C (30°F) or colder, low blower speeds will be selected and airflow will be directed on the windshield for 3 minutes. This is done to prevent windshield fogging. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, both air temperature actuators are in full hot position and outside air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will be out of automatic operation and not warm the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. On vehicle start up, the HVAC control module will monitor for conditions that indicate the possible presence of moisture in the HVAC module. To avoid blowing hot air and moisture out at the driver, the HVAC control module moves the mode door toward the floor and runs the low speed blower for a 3 seconds. This purge mode can be bypassed if the vehicle is started with the blower switch in maximum speed position. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, both air temperature actuators are in full cold position and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will be out of automatic operation and not cool the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

Air Distribution

When the mode switch is pressed, a ground is provided from the HVAC control module to the mode actuator through the mode door control circuits. When the mode actuator receives the signal, the mode actuator moves into the desired position.

The HVAC control module provides power and ground to the mode actuator. The HVAC control module receives power from the rear fuse block through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The mode actuator is a reverse polarity motor. Each circuit provides both power and ground to the mode actuator. When the mode actuator is being held in position, both of the mode door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a mode is requested, one of the mode door control circuits will ground, driving the mode actuator into the desired mode.

Front Defrost Mode

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When defrost is selected, by the vehicle operator, the A/C compressor is activated and outside air is brought into the vehicle. The blower motor will be activated, regardless of coolant temperature and air will be directed toward the windshield, the side windows and some air flow to the floor. Recirculation mode is not available in front defrost. The recirculation LED will flash on their respective displays if any of those switches are pressed when in front defrost mode. This indicates that these modes are not available. The rear window defogger does not affect the HVAC system in any setting.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Selection of the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Toggling the MODE button also activates the LCD display for the mode selected. If an airflow mode is currently displayed, pressing the MODE button selects the next air flow mode. The air flow direction will sequence through the following modes

1. MIX-BLEND. Air is directed through the floor, windshield, and side window outlets.
2. BI-LEVEL. Cool air is delivered through the vent outlets while warm air is delivered through the floor outlets.
3. FLOOR. Air is delivered though the floor, windshield and side window outlets.
4. VENT. Air is delivered through the instrument panel outlets.

These are the only air flow modes available through the MODE button. When in AUTO mode, the HVAC control module will only operate in the following modes

1. BI-LEVEL
2. VENT
3. FLOOR

Dual Zone Control Switch

The passenger air temperature switch is provided to allow the passenger to set air discharge temperatures on the passenger side of the vehicle. Passenger temperatures can be set from 15°C (60°F) to 32°C (90°F). To activate the dual zone, the passenger air temperature switch to the desired offset. If the passenger air temperature switch has been turned on, it can be turned off by pressing the passenger switch. Greater sunload on one side of the vehicle may cause the discharge air temperatures to be different, even when the HVAC system is not operating in a dual zone mode.

The HVAC control module provides power and ground to the passenger air temperature actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The passenger air temperature actuator is a reverse polarity motor. Each circuit provides both power and ground to the passenger air temperature actuator. When the passenger air temperature actuator is being held in position, both of the passenger air temperature door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a temperature offset is requested, one of the passenger air temperature door control circuits will ground, driving the passenger air temperature actuator into the desired temperature offset.

Air Temperature Description and Operation

The air temperature controls are divided into three primary areas

1. Automatic operation
2. The heating and air conditioning system
3. The A/C cycle

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 power mode master, provides a device on signal. The control module supports the following features

Air Temperature Description and Operation

Personalization

The HVAC control module will receive information that defines the current driver of the vehicle from the driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to three unique drivers

1. Driver set temperature
2. Passenger set temperature
3. Mode
4. Blower motor speed (auto, speed 1, 2, 3, 4, 5, 6)
5. A/C compressor request, auto ON or A/C OFF

This information shall be stored inside the HVAC control module memory. When a different driver identification button is selected the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned on, the last stored settings for the current driver will be activated except for the rear defrost and heated seat settings.

Air Temperature Actuators

The air temperature actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either a 0 or 12 volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 12 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.

The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across two commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.

Air Temperature Sensors

The air temperature sensors are 2-wire negative temperature coefficient thermistors. The vehicle uses the following air temperature sensors

1. Outside
2. Inside
3. Upper right
4. Upper left
5. Lower right
6. Lower left

The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). When temperature increases the sensor signal decreases. The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module detects that one of the duct temperatures must change, the HVAC control module will adjust the appropriate air temperature actuator. The following list shows the duct sensors that are monitored by the HVAC control module in each mode position

Air Temperature Description and Operation

If the HVAC control module detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored.

The inside temperature sensor operates within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). If the sensor is shorted to ground, an open, or shorted to voltage, the HVAC system will use a default value.

The outside temperature sensor operates within a temperature range between -30°C (-22°F) to 51°C (123.8°F). The radio displays the OAT value that it receives from the HVAC control module through a class 2 message. If the HVAC control module has determined that the outside temperature sensor has failed, the radio shall display, 75, in place of the outside air temperature. If the sensor is shorted to ground, an open, or shorted voltage, the HVAC control module will use a default value.

The radio displays the outside air temperature value that it receives from the HVAC control module through a class 2 message. The scan tool has the ability to update the displayed ambient air temperature. The outside air temperature value is displayed or updated under the following conditions

Air Temperature Description and Operation

Sunload Sensor

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The two sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If sensor is open or shorted, no sunload condition occurs.

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 A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists. The ECM disables the compressor clutch under the following conditions

1. A/C pressure is more than 2850 kPa (413 psi). The clutch will be enabled after the pressure decreases to less than 2100 kPa (254 psi).
2. A/C pressure is less than 204 kPa (30 psi). The clutch will be enabled after the pressure increases to more than 220 kPa (32 psi).

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will display A/C OFF on the module as long as the condition is present.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide the following

1. Heated air
2. Cooled air
3. Remove humidity from the interior of the vehicle
4. Reduce windshield fogging

Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve a 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

The HVAC control module commands or monitors the following actions when an air temperature setting is selected.

WARMEST POSITION - The air temperature actuator door position directs maximum air flow through the heater core.

COLDEST POSITION - The air temperature actuator door position directs maximum air flow around the heater core.

BETWEEN THE WARMEST AND COLDEST POSITION - The following sensors are monitored to direct the appropriate amount of air through the heater core to achieve the desired temperature

1. Sunload
2. Outside temperature
3. Inside temperature
4. Duct temperatures

The A/C system is engaged by selecting any switch on the HVAC control module except the, A/C OFF switch. The A/C switch will illuminate, A/C OFF, when the A/C switch is selected. The HVAC control module sends a class 2 A/C request message to the body control module (BCM) for A/C compressor clutch operation. The BCM must communicate with the ECM in order for the A/C clutch to be engaged. The HVAC system uses a compact variable swash plate compressor. The following conditions must be met in order for the ECM to turn on the compressor clutch from the HVAC control module request

1. BCM will allow A/C operation if the following limits are within normal operating range A/C line pressure A/C refrigerant low temperature Ambient temperature Engine coolant temperature Battery voltage
2. HVAC control module OAT temperature more than 1.5°C (35°F) Control module operating range 9 and 16 volts
3. ECM Engine coolant temperature (ECT) is less than 128°C (262°F) Engine RPM is more than 0 RPM A/C pressure is between 2850 kPa (413 psi) and 204 kPa (30 psi).

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

1. Throttle position is 100%
2. A/C pressure is more than 2850 kPa (413 psi)
3. A/C pressure is less than 204 kPa (30 psi)
4. Engine coolant temperature (ECT) is more than 128°C (262°F)

If there is a malfunction in the A/C system, the driver information center will read, SERVICE A/C SYSTEM, to alert the driver.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Dual Zone Operation

The HVAC control module has temperature settings for the driver and the passenger. If the passengers setting is turned off then the drivers setting controls both driver and passenger temperature actuators. The passengers setting can not be used without the drivers setting also being ON. The passengers setting can be turned ON or OFF by pressing the temperature switch on the passengers side of the HVAC control module. When the passengers setting is ON, the passenger temperature can be adjusted independently from the drivers setting and the passenger temperature is displayed on the passengers side of the control module. A different sunload or duct temperature on one side of the vehicle may cause different discharge air temperatures even when the passengers setting is not turned ON.

Automatic Operation

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in automatic mode, the following is required

1. The blower motor switch must be in the AUTO position.
2. The air temperature switch must be in any other position other than 60 or 90 degrees.
3. The mode switch must be in the AUTO position.

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically adjust to maintain the temperature selected, except in the extreme temperature positions. The HVAC control module performs the following functions to maintain the desired air temperature

1. Regulate blower motor speed
2. Position the air temperature actuator
3. Position the mode actuator
4. Position the recirculation actuator

When the warmest position is selected in automatic operation the blower speed, based on coolant temperature, will increase gradually until the vehicle reaches normal operating temperature. When normal operating temperature is reached the blower will stay on high speed and the air temperature actuators will stay in the full heat position. When the coldest position is selected in automatic operation the blower will stay on high and the air temperature actuators will stay in the full cold position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.

Engine Coolant

Engine coolant is the key element of the heating system. The engine thermostat controls the normal engine operating coolant temperature. Coolant pumped out of the engine enters the heater core through the inlet heater hose. The air flowing through the HVAC module absorbs the heat of the coolant flowing through the heater core. The coolant then exits the heater core through the heater outlet hose and returns back to the engine block.

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 a very low temperature gas that can transfer the undesirable heat from the passenger compartment to the outside air.

A Delphi model CVC-7 compressor is used on this model year vehicle. The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure in the A/C system. 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 high pressure A/C 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.

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 TXV.

The TXV is located at the evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the TXV, the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to boil at the TXV. 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 HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and back to the compressor, in a vapor state. This 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 HVAC module for passenger comfort. The moisture removed from the passenger compartment will also change form, or condense, and is discharged from the HVAC module as water.

Special Tools

Special Tools Illustration Tool Number/ Description J 38185 Hose Clamp Pliers J 39400-A Halogen Leak Detector J 42220 Universal 12V Leak Detection Lamp J 41447 R-134A A/C Tracer Dye - Box of 24 J 43600 ACR 2000 Air Conditioning Service Center J 43872 Fluorescent Dye Cleaner J 45037 A/C Oil Injector J 45268 A/C Flushing Adapter Kit J 45689 A/C Quick Joint Tool J 46297 A/C Dye Injector Kit J 46297-12 Replacement Dye Cartridges J 39200 Tech 2

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See also:
• Diagnostic System Check - Vehicle
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Control Module References
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Checking Aftermarket Accessories
• Leak Testing
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Odor Diagnosis
• Diagnostic Trouble Code (DTC) List - Vehicle
• Battery Negative Cable Disconnection and Connection
• Instrument Panel Accessory Trim Plate Replacement
• Fastener Notice
• Lifting and Jacking the Vehicle
• DTC B0159 or B0164
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• HVAC Compressor Clutch Does Not Engage
• HVAC Compressor Clutch Does Not Disengage
• Blower Motor Always On
• Blower Motor Inoperative
• Blower Motor Malfunction
• Sensor Resistance Table (Air Temperature Duct Sensor)
• Sensor Resistance Table (Inside and Ambient Air Temp Sensor)