HVAC System - Automatic Chevrolet Cab & Chassis Silverado 3500

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table (Primary HVAC)

Sensor Resistance Table (Primary HVAC)

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

Scheme 18

Scheme 19

Scheme 20

Scheme 21

Scheme 22

A/C Compressor Clutch Connector & Terminal Parts Information

A/C Compressor Clutch Terminal Identification

Scheme 23

A/C Low Pressure Switch Connector & Terminal Parts Information

A/C Low Pressure Switch Terminal Identification

Scheme 24

A/C Refrigerant Pressure Sensor Connector & Terminal Parts Information

A/C Refrigerant Pressure Sensor Terminal Identification

Scheme 25

Air Temperature Actuator - Left Connector & Terminal Parts Information

Air Temperature Actuator - Left Terminal Identification

Air Temperature Actuator - Right

Air Temperature Actuator - Right Connector & Terminal Parts Information

Air Temperature Actuator - Right Terminal Identification

Scheme 26

Air Temperature Sensor - Lower Left Connector & Terminal Parts Information

Air Temperature Sensor - Lower Left Terminal Identification

Air Temperature Sensor - Lower Right

Air Temperature Sensor - Lower Right Connector & Terminal Parts Information

Air Temperature Sensor - Lower Right Terminal Identification

Air Temperature Sensor - Upper Left

Air Temperature Sensor - Upper Left Connector & Terminal Parts Information

Air Temperature Sensor - Upper Left Terminal Identification

Air Temperature Sensor - Upper Right

Air Temperature Sensor - Upper Right Connector & Terminal Parts Information

Air Temperature Sensor - Upper Right Terminal Identification

Scheme 27

Air Temperature Sensor Assembly - Inside Connector & Terminal Parts Information

Air Temperature Sensor Assembly - Inside Terminal Identification

Scheme 28

Ambient Air Temperature Sensor Connector & Terminal Parts Information

Ambient Air Temperature Sensor Terminal Identification

Scheme 29

Ambient Light/Sunload Sensor Assembly Connector & Terminal Parts Information

Ambient Light/Sunload Sensor Assembly Terminal Identification

Scheme 30

Blower Motor Connector & Terminal Parts Information

Blower Motor Terminal Identification

Scheme 31

Blower Motor Control Processor Connector & Terminal Parts Information

Blower Motor Control Processor Terminal Identification

Scheme 32

HVAC Control Module - C1 Connector & Terminal Parts Information

HVAC Control Module - C1 Terminal Identification

Scheme 33

HVAC Control Module - C2 Connector & Terminal Parts Information

HVAC Control Module - C2 Terminal Identification

Mode Actuator

Mode Actuator Connector & Terminal Parts Information

Mode Actuator Terminal Identification

Recirculation Actuator

Connector & Terminal Parts Information

Recirculation Actuator Terminal Identification

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

PCM Scan Tool Output Controls

Scan Tool Data List

BCM Scan Tool Data List

HVAC Control Module Scan Tool Data List

PCM Scan Tool Data List

Circuit Description

The following DTCs are for the ambient air temperature sensor and for the inside air temperature sensor assembly

1. B0159 is for the ambient air temperature sensor.
2. B0164 is for the inside air temperature sensor assembly.

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 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 Range/Performance
2. DTC B0164 Passenger Compartment Temperature Sensor Circuit Range/Performance

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 0.09 volt or greater than 4.9 volts.

Action Taken When the DTC Sets

1. The HVAC control module uses a default value of 10°C (50°F) for the ambient air temperature display. The scan tool also displays 10°C (50°F) as the value for the Outside Air Temp. Raw parameter.
2. The HVAC control module use a default value of 25°C (77°F) for the Inside Air Temp. parameter.

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

1. 2: This step verifies that the condition that set the DTC is present.

DTC B0159 or B0164

The following DTCs are for the air temperature sensors located in the discharge air ducts

1. B0174 is for the upper left air temperature sensor.
2. B0179 is for the lower left air temperature sensor.
3. B0510 is for the upper right air temperature sensor.
4. B0515 is for the lower right air temperature sensor.

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.

This diagnostic procedure supports the following DTCs

1. DTC B0174 Output Air Temperature Sensor (Upper Left) Circuit Range/Performance
2. DTC B0179 Output Air Temperature Sensor 2 (Lower Left) Circuit Range/Performance
3. DTC B0510 Output Air Temperature Sensor 3 (Upper Right) Circuit Range/Performance
4. DTC B0515 Output Air Temperature Sensor 4 (Lower Right) Circuit Range/Performance

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

The HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.

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: This step verifies that the temperature displayed is not within the calibrated range.
2. 3: This step tests for the proper operation of the circuit in the high voltage range.
3. 4: This step 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 following DTCs are for the left and right sunload sensors.

1. B0183 is for the left sunload sensor.
2. B0188 is for the right sunload sensor.

The left and right sunload sensors provide the HVAC control module with inputs as to the amount heat load the sun is placing on the interior of the vehicle. The sunload sensors are photodiodes that are sensitive to light intensity. The body control module (BCM) applies 5 volts to internal input resistors that are connected to the left and right signal circuits of the sunload sensor assembly. The BCM provides ground to the sensors through the low reference circuit. The BCM monitors the voltage drops across the sunload sensors and converts the voltage values to count values where 1 volt is approximately equal to 51 counts. As the light intensity increases, the sunload sensors allow more current to travel through the circuits and the signal voltages decrease. As the light intensity decreases, the sunload sensors allow less current to travel through the circuits and the signal voltages increase. The BCM transmits the data to the HVAC control module over the class 2 serial data circuit.

This diagnostic procedure supports the following DTCs

1. DTC B1083 Solar Load Sensor Left Circuit
2. DTC B1088 Solar Load Sensor 2 Right Circuit

The ignition is ON.

The BCM determines that the value of the sunload sensor signal is less than 5 counts or greater than 250 counts.

The action taken will be for the BCM to revert to a calibrated default value.

1. The DTC will become history if the BCM 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.

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

1. 2: This step verifies that the value displayed is within the specified range.
2. 3: This step tests for the proper operation of the circuit in the high voltage range.
3. 4: This step 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 B0183 or B0188

The following DTCs are for the HVAC door actuators

1. B0229 is for the recirculation actuator.
2. B0414 is for the left air temperature actuator.
3. B0424 is for the right air temperature actuator.
4. 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.

This diagnostic procedure supports the following DTCs

1. DTC B0229 Recirculate Position Feedback Circuit Range/Performance
2. DTC B0414 Temperature Control 1 Feedback Circuit Range/Performance
3. DTC B0424 Temperature Control 2 Feedback Circuit Range/Performance
4. DTC B3770 Air Flow Control 6 Feedback Circuit

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.

Diagnostic Aids

1. If the condition is not present refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
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.

1. 3: At least 2 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: This step tests for the proper operation of the circuit in the low voltage range.
3. 6: This step 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: This step tests for a short to voltage in the 5-volt reference circuit.
5. 8: This step 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.

DTC B0229, B0414, B0424, or B3770

The following DTCs are for the HVAC door actuators

1. B0263 is for the mode actuator.
2. B0268 is for the recirculation actuator.
3. B0408 is for the left air temperature actuator.
4. 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.

This diagnostic procedure supports the following DTCs

1. DTC B0263 Air Flow Control 6 Circuit
2. DTC B0268 Air Flow Control 7 Circuit
3. DTC B0408 Temperature Control 1 Circuit
4. DTC B0418 Temperature Control 2 Circuit

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

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

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

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.

1. If the condition is not present refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
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.

1. 2: This step determines if the HVAC door actuator is stalled.
2. 3: This step applies control circuit voltage to the input of the HVAC door actuator.

DTC B0263, B0268, B0408, or B0418

The HVAC control module monitors the upper left and upper right duct temperature sensors when the mode switch is in the VENT or BI-LEVEL positions. The HVAC control module monitors the lower left and lower right duct temperature sensors when the mode switch is in the DEFOG, FLOOR or FRONT DEFROST positions. The duct sensors are used to measure the temperature of the air exiting the ducts to help maintain a consistent cabin air temperature. These duct sensor inputs provide the HVAC control module a way to determine if the engine needs to be started to maintain a specific air temperature. If an upper duct sensor circuit failure is detected the HVAC module will not request an engine start to help cool the cabin. A lower duct sensor circuit failure will not prevent the engine from starting.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B0989 Output Air Temperature Lower Sensors Correlation

The ignition has been in the OFF position for 4 hours.

1. After a 4-hour ignition OFF the difference of lower air temperature sensors count value is more than 40 counts.
2. After engine has started, within the first 20 minutes, and the conditions are present for the HVAC control module to place the air temperature doors to the maximum heat position and the air temperature sensor count value does not change at least 50 counts.
3. If the previous condition has passed a second 20-minute timer is started and conditions are present for maximum heat and the air temperature sensors are more than 40 counts apart any time during this second 20-minute timer.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The driver information center, if equipped, may display a message.
4. The HVAC control module will not request an engine restart while in continuous mode.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

1. If the condition is intermittent, refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. An air temperature sensor not installed properly in the HVAC duct may cause this DTC.
3. DTC B0174, B0179, B0510 and B0515 must be repaired before this diagnostic is completed or misdiagnosis will occur.

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

1. 2: This step tests to ensure that an air temperature sensor DTC did not cause this DTC.
2. 5: DTC B0989 sets only for the lower air temperature sensors. They HVAC system is placed in the Bi-Level mode and set to the coldest position to obtain a consistent temperature in the HVAC ducts. This action will determine if one of the air temperature sensors reading may be slightly higher or lower than the other air temperature sensors.
3. 6: The appropriate air temperature sensor is the sensor that is out of range compared to the other duct air temperature sensors.

DTC B0989

The HVAC control module monitors the upper left and upper right duct temperature sensors when the mode switch is in the VENT or BI-LEVEL positions. The HVAC control module monitors the lower left and lower right duct temperature sensors when the mode switch is in the DEFOG, FLOOR or FRONT DEFROST positions. The duct sensors are used to measure the temperature of the air exiting the ducts to help maintain a consistent cabin air temperature. These duct sensor inputs provide the HVAC control module a way to determine if the engine needs to be started to maintain a specific air temperature. If an upper duct sensor circuit failure is detected the HVAC module will not request an engine start to help cool the cabin. A lower duct sensor circuit failure will not prevent the engine from starting.

This diagnostic procedure supports the following DTC

DTC B0990 Output Air Temperature Upper Sensors Correlation

The ignition has been in the OFF position for 4 hours.

1. After a 4-hour ignition OFF the difference of lower air temperature sensors count value is more than 40 counts.
2. After engine has started, within the first 20 minutes, and the conditions are present for the HVAC control module to place the air temperature doors to the maximum heat position and the air temperature sensor count value does not change at least 50 counts.
3. If the previous condition has passed a second 20-minute timer is started and conditions are present for maximum heat and the air temperature sensors are more than 40 counts apart any time during this second 20-minute timer.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The driver information center, if equipped, may display a message.
4. The HVAC control module will not request an engine restart while in continuous mode.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

1. If the condition is intermittent, refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. An air temperature sensor not installed properly in the HVAC duct may cause this DTC.
3. DTC B0174, B0179, B0510 and B0515 must be repaired before this diagnostic is completed or misdiagnosis will occur.

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

1. 2: This step tests to ensure that an air temperature sensor DTC did not cause this DTC.
2. 5: DTC B0989 sets only for the lower air temperature sensors. The HVAC system is placed in the Bi-Level mode and set to the coldest position to obtain a consistent temperature in the HVAC ducts. This action will determine if one of the air temperature sensors reading may be slightly higher or lower than the other air temperature sensors.
3. 6: The appropriate air temperature sensor is the sensor that is out of range compared to the other duct air temperature sensors.

DTC B0990

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.

This diagnostic procedure supports the following DTC

DTC B1375 Device Ignition 3 Circuit

1. Source voltage is 8.7-16.5 volts.
2. The HVAC control module receives a RUN power mode message from the body control module (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.

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.

DTC B1375

The powertrain control module (PCM) or engine control module (ECM) 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.

This diagnostic procedure supports the following DTC

DTC P0530 Air Conditioning Refrigerant Pressure Sensor Circuit

The PCM/ECM detects an A/C request.

1. The A/C refrigerant pressure sensor signal is less than 0.1 volt 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/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.

For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections .

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

1. 3: This step tests for the proper operation of the circuit in the low voltage range.
2. 4: This step 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: This step tests for a short to voltage in the 5-volt reference circuit.
4. 6: This step tests for a high resistance or an open in the low reference circuit.

DTC P0530 (LU3, LR4, LM7, LQ4 and L18)

The engine control module (ECM) 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 powertrain control module (PCM) will not allow the A/C compressor clutch to engage.

This diagnostic procedure supports the following DTC

DTC P0530 Air Conditioning Refrigerant Pressure Sensor Circuit

The ECM 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 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.

For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections .

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

1. 5: This step tests the ability of the A/C refrigerant pressure sensor to create a voltage signal for the ECM to monitor the A/C refrigerant pressure. Measure the voltage at the A/C refrigerant pressure sensor, if the voltage is measured at the connector for the sensor, misdiagnosis will occur.

DTC P0532 or P0533

Symptoms - HVAC Systems - Automatic

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) , 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»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation) «Air Temperature Description and Operation»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-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»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__checking-aftermarket-accessories) .
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»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-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 .

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»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «HVAC Compressor Clutch Does Not Disengage»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Blower Motor Always On»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Blower Motor Inoperative»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
6. «Too Hot in Vehicle»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
7. «Too Cold in Vehicle (With HP2)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic) or «Too Cold in Vehicle (With Out HP2)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
8. «Air Delivery Improper»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic)
9. «Air Recirculation Malfunction»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-recirculation-malfunction)
10. «Leak Testing»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
11. «Noise Diagnosis - Blower Motor»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor)
12. «Noise Diagnosis - Air Conditioning (A/C) System»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac)
13. «Noise Diagnosis - HVAC Module»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module)
14. «Odor Diagnosis»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis)

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 138-172 kPa (20-25 psi).
3. Throttle angle is at 100 percent.
4. Engine speed is more than 5,500 RPM.
5. Engine coolant temperature (ECT) is more than 121°C (250°F).
6. Ambient air temperature is less than 5°C (40°F).
7. Engine is idling at a low unstable RPM

Compressor clutch engagement cannot be used to determine status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.

To accurately determine what pressure the A/C low pressure switch opens and closes at use Kent Moore GE-47742 which will allow the technician to measure the switch point pressure at the switch.

Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the switch to determine the switch points of the low pressure switch.

The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The "plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer.

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

1. 2: The A/C compressor output is disabled if the engine is idling at a low unstable RPM.
2. 3: 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.
3. 4: This step ensures that the HVAC control module is receiving an input from the A/C switch.
4. 5: These actions will enable the A/C compressor to operate.
5. 6: 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.
6. 8: The A/C Low Pressure Switch parameter is out of range when the HVAC control module interprets the signal being below 138-172 kPa (20-25 psi).
7. 9: 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.
8. 12: The A/C compressor relay output from the PCM is disabled if the A/C high side system pressure is interpreted to be higher than 2 958 kPa (429 psi).

HVAC Compressor Clutch Does Not Engage

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

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

HVAC Compressor Clutch Does Not Disengage

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

1. 4: The blower motor parameter must be commanded ON before an OFF command will function.

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

1. 2: This step verifies that the HVAC control module Fan Up Switch parameter matches the requested state of the blower motor switch.
2. 3: This step verifies that the HVAC control module Fan Down Switch parameter matches the requested state of the blower motor switch.

Blower Motor Malfunction

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. The air temperature actuators can be calibrated. Refer to «Actuator Recalibration»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

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

1. 6: The ambient air temperature (AAT) must be above 5°C (40°F) in order for this A/C compressor test to be run.
2. 8: This step ensures that the lower air temperature sensors operate properly. The LH and RH Heater Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
3. 9: This step ensures that the upper air temperature sensors operate properly. The LH and RH AC Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
4. 11: This action ensures that the internal fan of the inside air temperature sensor assembly is providing air flow across the internal sensor.
5. 14: Use the following table to determine that the recorded scan tool values are within range for the recorded probe temperatures of the J 43600 ACR 2000 Air Conditioning Service Center.

Too Hot in Vehicle

Too Hot in Vehicle

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. The air temperature actuators can be calibrated. Refer to «Actuator Recalibration»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

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

1. 10: This step ensures that the lower air temperature sensors operate properly. The LH and RH Heater Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensor circuits or the sensor itself, then the count value of the affected sensor would remain high.
2. 11: This step ensures that the upper air temperature sensors operate properly. The LH and RH AC Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensor circuits or the sensor itself, then the count value of the affected sensor would remain high.
3. 13: This action ensures that the internal fan of the inside air temperature sensor assembly is providing air flow across the internal sensor.
4. 17: Use the following table to determine that the recorded scan tool values are within range for the recorded probe temperatures.

Too Cold in Vehicle (With HP2)

Too Cold in Vehicle (With HP2)

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. The air temperature actuators can be calibrated. Refer to «Actuator Recalibration»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

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

1. 8: This step ensures that the lower air temperature sensors operate properly. The LH and RH Heater Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
2. 9: This step ensures that the upper air temperature sensors operate properly. The LH and RH AC Duct Actual parameter count values should lower as the air temperature of the ducts get warmer. If there is a high resistance in either of the air temperature sensors circuits or the sensor itself then the count value of the effected sensor would remain high.
3. 11: This action ensures that the internal fan of the inside air temperature sensor assembly is providing air flow across the internal sensor.
4. 15: Use the following table to determine that the recorded scan tool values are within range for the recorded probe temperatures.

Too Cold in Vehicle (With Out HP2)

Too Cold in Vehicle (With Out HP2)

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
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

Air Delivery Improper

Air Recirculation Malfunction

Air Recirculation Malfunction

Actuator Recalibration

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

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

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

Preferred Method (w/Scan Tool)

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

Alternate Method (w/o Scan Tool)

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

Removal Procedure

1. Remove the instrument panel accessory trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Remove the screws from the HVAC control module.
3. Depress the control assembly retaining tabs and remove the HVAC control module from the instrument panel.
4. Disconnect the electrical connectors from the HVAC control module.

Installation Procedure

1. Connect the electrical connectors to the HVAC control module.
2. Install the HVAC control module into the instrument panel, ensuring that the HVAC control module retaining tabs lock into place.
3. Install the screws from the HVAC control module. Tighten: Tighten the screws to 1.9 N.m (17 lb in).
4. Install the instrument panel accessory trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
5. Start the vehicle and let run for one minute.
6. Refer to «Control Module References»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for programming and setup information.

1. If equipped, remove the sound insulator panel. Refer to «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Disconnect the electrical connector at the blower motor.
3. Disconnect the electrical connector (4) from the blower motor control processor (2).
4. Remove the blower motor control processor retaining screws (3) from the HVAC module (1).
5. Remove the blower motor control processor (2) from the HVAC module (1).

1. Install the blower motor control processor (2) to the HVAC module (1).
2. Install the blower motor control processor retaining screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector (4) to the blower motor control processor (2).
4. Connect the electrical connector at the blower motor.
5. If equipped, install the sound insulator panel. Refer to «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the air distribution duct. Refer to «Air Distributor Duct Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect the electrical connection from the recirculation actuator (1).
3. Remove the recirculation actuator retaining screws.
4. Remove the recirculation actuator.

1. Install the recirculation actuator.
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»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the floor air outlet duct extension (1) from the floor duct (2).
2. Remove the center console. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
3. Remove the screws from the center console duct.
4. Remove the center console duct.
5. Disconnect the electrical connection from the mode actuator (10).
6. Remove the mode actuator mounting screws from the HVAC module.
7. Remove the mode actuator as an assembly with the actuator cam.

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.
2. Install the mode actuator mounting screws to the HVAC module. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connection at the mode actuator (10).
4. Install the center console duct.
5. Install the screws to the center console duct. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
6. Install the center console. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
7. Install the floor air outlet duct extension (1) to the floor air duct (2).

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the floor air outlet duct extension (1) from the floor duct (2).
2. Remove the body control module. Refer to «Body Control Module Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/communication-devices/#data-communication-system) .
3. Disconnect the electrical connection at the mode actuator (10).
4. Remove the mode actuator mounting screws from the HVAC module.
5. Remove the mode actuator as an assembly with the actuator cam.

1. Install the mode actuator as an assembly with the actuator cam. Line up the heater/defroster lever with the mode actuator cam slot. Line up the A/C lever with the mode actuator cam.
2. Install the mode actuator mounting screws to the HVAC module. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connection at the mode actuator (10).
4. Install the body control module. Refer to «Body Control Module Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/communication-devices/#data-communication-system) .
5. Install the floor air outlet duct extension (1) to the floor air duct (2).

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the I/P carrier. Refer to «Instrument Panel Carrier Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
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).

1. Install the right air temperature actuator (3) from the HVAC module assembly (2).
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 Carrier Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
5. Reprogram the air temperature actuator. Refer to «Actuator Recalibration»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the center console, if equipped. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Remove the instrument panel (I/P) insulator panel. Refer to «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
3. Disconnect the electrical connector (1) from the left air temperature actuator (2).
4. Remove the screws from the left air temperature actuator (2).
5. Remove the left air temperature actuator (2) from the HVAC module assembly (3).

1. Install the left air temperature actuator (2) to the HVAC module assembly (3).
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 «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
5. Install the center console, if equipped. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
6. Reprogram the left air temperature actuator. Refer to «Actuator Recalibration»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

1. Remove the I/P upper trim panel. Refer to «Instrument Panel Upper Trim Panel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) ..
2. Disconnect the electrical connector (1) from the upper right air temperature sensor (2).
3. Remove the upper right air temperature sensor (1) from the air distributor duct (3).

1. Install the upper right air temperature sensor (1) to the air distributor duct (3).
2. Connect the electrical connector (1) from the upper right air temperature sensor (2).
3. Install the I/P upper trim panel. Refer to «Instrument Panel Upper Trim Panel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

1. Remove the upper left air temperature sensor (2) from the air distributor duct (1).
2. Disconnect the electrical connector (3) from the upper left air temperature sensor (2).

1. Install the upper left air temperature sensor (2) to the air distributor duct (1).
2. Connect the electrical connector (3) to the upper left air temperature sensor (2).

1. Disconnect the electrical connector from the lower left air temperature sensor (1).
2. Remove the lower left air temperature sensor (1) from the HVAC module (2).

1. Install the lower left air temperature sensor (1) to the HVAC module (2).
2. Connect the electrical connector to the lower left air temperature sensor (1).

1. Remove the I/P lower closeout panel. Refer to «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Remove the right floor duct. Refer to «Floor Air Outlet Duct Replacement - Right Side»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
3. Remove the center console. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
4. Disconnect the electrical connector from the lower right air temperature sensor (1).
5. Remove the lower right air temperature sensor (1).

1. Install the lower right air temperature sensor (1).
2. Connect the electrical connector to the lower right air temperature sensor (1).
3. Install the center console. Refer to «Console Replacement (w/Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Console Replacement (w/o Console Mounting)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
4. Install the right floor duct. Refer to «Floor Air Outlet Duct Replacement - Right Side»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
5. Install the I/P lower closeout panel. Refer to «Instrument Panel Insulator Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

1. Remove the park/turn signal. Refer to «Park/Turn Signal Lamp Replacement (Old Style)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exterior-lights/#lighting-system) .
2. Disconnect the electrical connector from the ambient air temperature sensor (3).
3. Remove the ambient air temperature sensor (3).

1. Install the ambient air temperature sensor (3).
2. Connect the electrical connector to the ambient air temperature sensor (3).
3. Install the park/turn signal. Refer to «Park/Turn Signal Lamp Replacement (Old Style)»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exterior-lights/#lighting-system) .

1. Remove the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
2. Remove the left center pillar assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
3. Remove the left center pillar garnish molding. Refer to «Center Pillar Garnish Molding Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
4. Remove the left sunshade. Refer to «Sunshade Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
5. Gently pull down the headliner.
6. Disconnect the electrical connector from the inside air temperature sensor.
7. Partially remove the inside air temperature sensor from the headliner.
8. Remove the sensor grille from the inside air temperature sensor.
9. Remove the inside air temperature sensor from the headliner.

1. Install the new sensor grille to the headliner.
2. Install the inside air temperature sensor to the headliner and sensor grille.
3. Connect the electrical connector to the inside air temperature sensor.
4. Install the left sunshade. Refer to «Center Pillar Garnish Molding Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
5. Install the left center pillar garnish molding. Refer to «Center Pillar Garnish Molding Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
6. Install the left center assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
7. Install the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#interior-trim-and-paneling) .

1. Remove the instrument panel (I/P) upper trim panel. Refer to «Instrument Panel Upper Trim Panel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) ..
2. Remove the sun load sensor (2) from the upper trim panel.
3. Disconnect the electrical connector.

1. Connect the electrical connector.
2. Install the sun load sensor (2) to the upper trim panel.
3. Install the I/P upper trim panel. Refer to «Instrument Panel Upper Trim Panel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) ..

Air Delivery Description and Operation

The air delivery description and operation is divided into 5 areas

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

HVAC Control Components

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

Air Delivery Description and Operation

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.

Blower Motor Control Processor

The blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the blower motor. The HVAC control module provides a low side pulse width modulated signal to the blower motor control processor over the blower motor speed control circuit. As the requested blower speed increases, the HVAC control module increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the HVAC control module decreases the amount of time that the signal is modulated to ground.

Air Speed - Front Control

The blower control switch is integrated into the HVAC control module. The 2 rocker type switches provide the vehicle operator the ability to select several blower speeds. The HVAC control module uses a bar graph type display to indicate the selected blower speed. The HVAC control module provides a pulse width modulated (PWM) signal to the blower motor through the blower motor speed control circuit. The blower motor changes speed based on the received PWM signal from the HVAC control module. Power and ground are provided to the blower motor through the battery positive voltage and ground circuits. When the HVAC control module is operating in AUTO mode, the system automatically controls the blower speed. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.

Air Distribution

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

1. Defrost
2. Defog
3. Panel
4. BI-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.

Mode Actuator

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.

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.

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 Auto switch must be activated.
2. The air temperature switch must be in any other position other than full hot or full cold position.

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

1. Monitor the following sensors: Inside air temperature sensor Ambient Air Temperature Sensor Lower Left Air Temperature Sensor Lower Right Air Temperature Sensor Upper Left Air Temperature Sensor Upper Right Air Temperature Sensor
2. Regulate blower motor speed
3. Position the air temperature actuator
4. Position the mode actuator
5. Position the recirculation actuator
6. Request A/C operation

Air Temperature Description and Operation

The air temperature controls are divided into 5 areas

1. HVAC Control Components
2. Heating and A/C Operation
3. Automatic Operation
4. Engine Coolant
5. 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 mode master, provides a device on signal. The control module supports the following features

Air Temperature Description and Operation

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.

Air Temperature Sensors

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors

1. Ambient Air Temperature Sensor
2. Inside Air Temperature Sensor Assembly
3. Upper Left Air Temperature Sensor
4. Upper Right Air Temperature Sensor
5. Lower Left Air Temperature Sensor
6. Lower Right Air Temperature Sensor

A signal and a low-reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40°C (-40°F) to 101°C (215°F). The sensor signal varies between 0-5 volts.

The input of the duct air temperature sensors are different from the ambient and inside sensors. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease.

If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the ambient and inside air temperature sensors will be displayed on the scan tool. The default value for the duct air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

The ambient air temperature sensor mounts underhood and can be affected by city traffic, by idling, and by restarting a hot engine. Therefore, the HVAC control module filters the value of the ambient air temperature sensor for temperature display. The ambient air temperature value is updated under the following conditions

Air Temperature Description and Operation

The scan tool has the ability to update the displayed ambient air temperature. To update the ambient air temperature display on the HVAC control module, perform the following procedure: Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.

1. Turn ON the ignition.
2. Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.

Sunload Sensor Assembly

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly. Low reference and signal circuits enable the sensor to operate. As the light shining upon the sensor gets brighter, the sensor resistance increases. The sensor signal decreases as the resistance increases. 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 the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted sunload value. This value will not be displayed on the scan tool. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is fixed. The scan tool parameter for the sunload sensor is the actual state of the signal circuit.

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 5 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 138-172 kPa (20-25 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275-317 kPa (40-46 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. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. The vehicle passenger can offset the passenger temperature as much as 16.7°C (30°F). 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

The control module makes the following actions when automatic operation is not selected, and an air temperature setting is selected

1. When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.
2. When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.
3. When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired temperature: Sunload Duct temperatures Ambient temperature Inside temperature

The A/C system can be engaged by either pressing the A/C switch or during automatic operation. 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.

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

1. The ambient air temperature is above 4°C (40°F).
2. The A/C low pressure switch signal circuit is grounded.
3. The A/C refrigerant pressure sensor parameter is less than 2957 kPa (429 psi).
4. The PCM receives an A/C request from the HVAC control module.
5. The 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. The ambient air temperature is less than 4°C (40°F).
2. The throttle position is 100%.
3. The A/C low pressure switch is open.
4. The A/C high side pressure is more than 2957 kPa (429 psi).
5. The A/C low side pressure is less than 151 kPa (22 psi).
6. The engine coolant temperature (ECT) is more than 121°C (250°F).
7. The engine speed is more than 5500 RPM.
8. Transmission shift
9. The PCM detects excessive torque load.
10. The PCM detects insufficient idle quality.
11. The PCM detects a hard launch condition.

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 Auto switch must be activated
2. The air temperature switch must be in any other position other than full hot or full cold position

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

1. Monitor the following sensors: Inside Air Temperature Sensor Ambient Air Temperature Sensor Lower Left Air Temperature Sensor Lower Right Air Temperature Sensor Upper Left Air Temperature Sensor Upper Right Air Temperature Sensor
2. Regulate blower motor speed
3. Position the air temperature actuator
4. Position the mode actuator
5. Position the recirculation actuator
6. Request A/C operation

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.

Auxiliary Coolant Pump (w/HP2)

The auxiliary coolant pump circulates coolant through the engine and heater core when HVAC requires heating and the engine is HOT and OFF. The HCM will turn on the auxiliary coolant pump when the HVAC control module commands it to do so by sending a class 2 signal to the HCM.

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 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, 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.

See also:
• Diagnostic System Check - Vehicle
• Testing for Intermittent Conditions and Poor Connections
• Circuit Testing
• Wiring Repairs
• Connector Repairs
• Control Module References
• Diagnostic Trouble Code (DTC) List - Vehicle
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Checking Aftermarket Accessories
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Noise Diagnosis - HVAC Module
• Odor Diagnosis
• HVAC Schematics (Manual - CJ3)
• Rough, Unstable, or Incorrect Idle and Stalling
• Air Conditioning (A/C) System Performance Test (Diesel Engine)
• Heating Performance Diagnostic
• Auxiliary Water Pump Replacement
• Instrument Panel Cluster Trim Plate Bezel Replacement
• FASTENER NOTICE
• Body Control Module Replacement
• Park/Turn Signal Lamp Replacement (Old Style)
• Windshield Pillar Garnish Molding Replacement
• DTC B0159 or B0164
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• Blower Motor Inoperative
• Air Recirculation Malfunction
• Actuator Recalibration
• Sensor Resistance Table (Primary HVAC)