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HVAC System - Automatic: Other Cadillac SRX II facelift

Automatic HVAC System ~5503 words

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Verify DTCs B0163 and B0183 are not both set concurrently. If both DTCs are set Refer to «Low Reference Test»(ref-644765-S07506859062014072300000) . If both DTCs are not set
  2. Verify DTC B0163, B0183, or B1405 is not set. If one of the DTCs is set Refer to the appropriate diagnostic in Circuit/System Testing (below). If none of the DTCs are set
  3. Verify the B10B Ambient Light/Sunload Sensor is accurate. If the sensor is not accurate Perform the following Circuit/System Testing in the order listed below: Circuit/System Testing - Low Reference Test Circuit/System Testing - DTC B0163 Circuit/System Testing - DTC B1405 Circuit/System Testing - DTC B0183 If the sensor is accurate
  4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify the appropriate temperature sensor has a parameter displayed in HVAC scan tool information. If there is no scan tool parameter Refer to «Circuit/System Testing - Without Scan Tool Support»(ref-644765-S41232233212014072300000) . If there is a scan tool parameter
  3. Refer to «Circuit/System Testing - With Scan Tool Support»(ref-644765-S41232233212014072300000)

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

  1. Perform the «Actuator Recalibration»(ref-644765-S14650276342014072300000) procedure.
  2. Verify the concern or DTC has been corrected. If the concern or DTC has not been corrected Verify DTC B023A is not set. If DTC B023A is set, refer to «Circuit/System Testing - DTC B023A»(ref-644765-S31248809792014072300000) . If DTC B023A is not set, refer to «Circuit/System Testing - DTC B0223, B022A, B0233, B0408, B0418, B0428 or B3531»(ref-644765-S31248809792014072300000) . If the concern or DTC has been corrected
  3. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON.
  2. Verify DTC B1020 39 is not set. If the DTC is set Replace the K33A HVAC Control Module - Auxiliary. If the DTC is not set
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for HVAC control module - auxiliary replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON
  2. Verify the scan tool engine control module A/C High Side Pressure Sensor parameter is between 6.8 kPa (1 psi) and 2950 kPa (428 psi). If not between 6.8 kPa (1 psi) and 2950 kPa (428 psi) Refer to Circuit/System Testing (below). If between 6.8 kPa (1 psi) and 2950 kPa (428 psi)
  3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for engine control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for engine control module replacement, programming and setup

Symptoms - HVAC Systems - Automatic

Note. Perform the Diagnostic System Check - Vehicle before using the Symptom Tables in order to verify that all of the following conditions are true: There are no DTCs set. The control modules can communicate via the serial data link. Review the system operation in order to familiarize yourself with the system functions. Refer to Steering Wheel Controls Description and Operation .

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J43600 ACR Air Conditioning Service Center

Note. Check for bulletins before proceeding.

  1. Ignition ON.
  2. Verify every applicable scan tool Switch parameter changes when pressing the appropriate switch on the A20 Radio/HVAC Controls. If any parameter does not change Replace the A20 Radio/HVAC Controls. If all parameters change
  3. Verify every applicable scan tool Switch parameter changes when pressing the appropriate switch on the K33A HVAC Control Module - Auxiliary. If any parameter does not change Replace the K33A HVAC Control Module - Auxiliary. If all parameters change
  4. Verify the front blower motor operates properly with the blower motor switch in each speed position. If the front blower motor does not operate in each speed position Refer to «DTC B0193»(ref-644765-S32078383182014072300000) . If the front blower motor operates properly in each speed position
  5. Verify the rear blower motor operates properly with the blower motor switch in each speed position. If the rear blower motor does not operate in each speed position Refer to «DTC B0208»(ref-644765-S34117475722014072300000) . If the rear blower motor operates properly in each speed position
  6. Verify the HVAC doors listed below move when pressing the appropriate switch. Driver Temperature Passenger Temperature Mode Recirculation Auxiliary Mode Auxiliary Temperature If any HVAC door does not move Refer to «DTC B0223, B022A, B0233, B023A, B0408, B0418, B0428, or B3531»(ref-644765-S00574069702014072300000) . If all HVAC doors move
  7. Install the J43600 ACR Air Conditioning Service Center.
  8. Verify the high side pressure reading on the Air Conditioning Service Center is within 10% of the scan tool ECM A/C High Side Pressure Sensor parameter. If the reading is not within 10% Refer to «DTC P0532 or P0533»(ref-644765-S36644700692014072300000) . If the reading is within 10%
  9. Verify the A/C High Side Pressure Sensor parameter is between 269-2929 kPa (39-425 PSI). If the reading is not between 269-2929 kPa (39-425 PSI) Refer to «Air Conditioning (A/C) System Performance Test (LF1 or LFX)»(ref-644713-S24514793702014072300000) . If the reading is between 269-2929 kPa (39-425 PSI)
  10. Verify the scan tool parameters listed below are within 10% of ambient temperature. Lower Left Duct Air Temperature Sensor Upper Left Duct Air Temperature Sensor Lower Right Duct Air Temperature Sensor Upper Right Duct Air Temperature Sensor A/C Evaporator Temperature Sensor Lower Auxiliary Duct Air Temperature Sensor Upper Auxiliary Duct Air Temperature Sensor If not within 10% of ambient temperature Refer to «DTC B0173, B0178, B0509, B0514, B0519, B3583, or B3933»(ref-644765-S17035144162014072300000) . If within 10% of ambient temperature
  11. Verify the scan tool parameters listed below are within 10% of actual conditions. Passenger Compartment Humidity Passenger Compartment Humidity Sensor Temperature Passenger Compartment Windshield Temperature If not within 10% of actual conditions Refer to «DTC B018A, B048C, B048F, or B1395»(ref-644765-S26070342662014072300000) . If within 10% of actual conditions
  12. Engine ON, A/C system ON.
  13. Verify cool air flows from the ducts with the temperature control in the coldest position. If the air is not cool Verify the Q2 A/C Compressor Clutch is engaged. If the Q2 A/C Compressor Clutch is not engaged, refer to «Air Conditioning Compressor Malfunction»(ref-644765-S23368018272014072300000) . If the Q2 A/C Compressor Clutch is engaged, refer to «Air Conditioning (A/C) System Performance Test (LF1 or LFX)»(ref-644713-S24514793702014072300000) , and «DTC B393B»(ref-644765-S18871152272014072300000) . If the air is cool
  14. Verify warm air flows from the ducts with the temperature control in the warmest position. If the air is not warm Refer to «Heating Performance Diagnostic»(ref-644713-S04678976592014072300000) . If the air is warm
  15. Engine OFF, ignition ON.
  16. Verify the Air Quality Sensor parameter changes while introducing hydrocarbons from a suitable source into the vicinity of the B108 Air Quality Sensor. If the Air Quality Sensor parameter does not change Refer to «DTC B3843»(ref-644765-S18816462822014072300000) . If the Air Quality Sensor parameter changes
  17. Verify the scan tool Sunload parameter changes while covering the B10B Ambient Light/Sunload Sensor with a shop towel and changes when shining a bright light on it. If the Sunload parameter does not change Refer to «DTC B0163, B0183, or B1405»(ref-644765-S00154195612014072300000) . If the Sunload parameter changes
  18. Verify the actual inside air temperature, using a thermometer, is less than 3°C (5°F) difference from the scan tool Inside Passenger Compartment Air Temp. Sensor parameter. If greater than a 3°C (5°F) difference Refer to «DTC B0163, B0183, or B1405»(ref-644765-S00154195612014072300000) . If less than a 3°C (5°F) difference
  19. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

Schematic Reference

HVAC Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(ref-644726-S12298670162014072300000)
  2. «Connector Repairs»(ref-644726-S09053351542014072300000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-644726-S21103124652014072300000)
  4. «Wiring Repairs»(ref-644726-S20665353652014072300000)

Scan Tool Reference

Control Module References for scan tool information

Note. Refer to HVAC System Malfunction before performing this procedure.

  1. Ignition ON, press and release the A/C Switch.
  2. Verify the HVAC control module scan tool A/C Request Signal parameter changes between Active and Inactive. If the parameter does not change Replace the A20 Radio/HVAC Controls. If the parameter changes
  3. Set A/C system to coolest setting with blower ON.
  4. Press and release the A/C switch several times.
  5. Verify the ECM scan tool A/C Request Signal parameter changes between Active and Inactive. If the parameter does not change Replace the K33 HVAC Control Module. If the parameter changes
  6. Verify the A/C compressor clutch engages when commanding the ECM A/C Relay output function On and Off with a scan tool. If the A/C compressor clutch does not engage Refer to «DTC P0645, P0646, or P0647»(ref-644765-S41889169862014072300000) If the A/C compressor clutch engages
  7. Engine ON.
  8. Verify the HVAC control module scan tool A/C Compressor Refrigerant Solenoid Valve Command parameter changes with varying cooling loads. If the parameter does not change Refer to «DTC B393B»(ref-644765-S18871152272014072300000) If the parameter does change
  9. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-644765-S40153420582014072300000)
  2. «Control Module References»(ref-644727-S14842497662014072300000) for HVAC control module replacement, programming and setup

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. Build the vehicle with the scan tool.
  4. Select Module Diagnosis.
  5. Select Remote Heater and Air Conditioning Control Module.
  6. Select Configuration/Reset Functions.
  7. Select HVAC Afterblow Configuration.

When afterblow has been enabled by the scan tool the blower motor will operate at 68% blower speed, following the sequence below up to 5 times. This could last up to an hour

  1. The blower motor will be OFF for 7-11 minutes.
  2. The blower motor will RUN for 25-30 seconds.

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

  1. The engine must be turned off for at least 30 min.
  2. The outside air temperature must be at least 21°C (70°F).
  3. The A/C compressor must have operated for more than 2 minutes before shut down during the latest key cycle.
  4. The system voltage must be at least 12 V.

HVAC Control Components

Radio/HVAC Control

The Radio/HVAC control contains all switches, which are required to control the functions of HVAC and serve as interface between the operator and the HVAC control module. The selected values are passed to the HVAC control module via LIN-Bus.

Radio/HVAC Control - Auxiliary (CJ4 only)

The Radio/HVAC control - auxiliary contains all switches, which are required to control the functions of rear HVAC and serve as interface between the operator and the HVAC control module. The selected values are passed to the HVAC control module via LIN-Bus.

HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain and control desired air temperature and air distribution settings. The battery positive voltage circuit provides power that the HVAC control module uses for keep alive memory. If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from keep alive memory. The body control module (BCM), which is the vehicle mode master, provides a device ON-Signal. The HVAC control module provides blower, air delivery mode and air temperature settings.

The HVAC control module supports the following features

FeatureAvailability
AfterblowAvailable if reprogrammed by the technician
PurgeYes
PersonalizationYes
Actuator CalibrationYes

Mode Actuator (Front)

The mode actuator is a 5-wire stepper motor. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the mode flap into the calculated position in order to reach the selected position. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Mode Actuator - Rear (CJ4 only)

The mode actuator is a 5-wire stepper motor. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the mode flap into the calculated position in order to reach the selected position. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Air Temperature Actuators (Front)

The interior temperature can be selected separately for the driver and passenger. For this purpose, two stepper motors are used that regulates two mixed air flaps independently of each other. The air temperature actuators are 5-wire stepper motors. The HVAC control module supplies a 12 V reference voltage to each stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The left air temperature actuator moves the left mixed air flap into the calculated position, in order to reach the selected temperature of the left temperature switch. The right air temperature actuator puts the right mixed air flap into the calculated position, in order to reach the selected temperature of the right temperature switch. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Air Temperature Actuator - Rear (CJ4 only)

The interior temperature can be selected separately for the rear passengers. The air temperature door actuator - auxiliary is a 5-wire stepper motor. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The air temperature door actuator - auxiliary moves the rear mixed air flap into the calculated position, in order to reach the selected temperature of the rear temperature switches. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Recirculation Actuator

The recirculation actuator is a 5-wire stepper motor. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the recirculation flap into the calculated position in order to reach the desired position. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Air Inlet Actuator

The air inlet actuator is a 5-wire stepper motor. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor moves the air inlet flap into the calculated position, in order to reach the selected position. The null point of the stepper motor will be calibrated, if the stepper motor is new. When the stepper motor is calibrated, the HVAC control module can drive the applicable coil to reach exactly the desired position of the flap.

Blower Motor Control Processor (Front)

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 modulation (PWM) signal to the blower motor control processor via 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.

Blower Motor Control Processor - Rear (CJ4 only)

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 modulation (PWM) signal to the blower motor control processor via 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.

Duct Temperature Sensors

The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The sensors operate within a temperature range of -40 to +85°C (-40 to +185°F). The sensors are installed in the air distribution ducts and measure the temperature of the air that streams from the ducts. The HVAC control module uses these values to calculate the mixed air flap position.

Evaporator Temperature Sensor

The evaporator temperature sensor is a 2-wire negative temperature co-efficient thermistor. The sensor operates within a temperature range of -40 to +85°C (-40 to +185°F). The sensor is installed at the evaporator and measures its temperature. If the temperature drops under 3°C (38°F), the compressor will be switched off in order to prevent a frozen evaporator.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5 V reference voltage, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0.2-4.8 V. When the A/C refrigerant pressure is low, the signal value is near 0 V. When the A/C refrigerant pressure is high, the signal value is near 5 V. The engine control module (ECM) converts the voltage signal to a pressure value. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

A/C Compressor

The A/C compressor is constantly belt driven. The performance of the A/C compressor is regulated per a lifting magnet in the A/C compressor. The HVAC control module supplies battery voltage to the A/C compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width modulation (PWM) signal to the A/C compressor in order to command the performance of the A/C compressor. The performance of the A/C compressor is regulated according to adjusted interior temperature on the basis of characteristic lines. Therefore the HVAC control module grounds the A/C compressor with the PWM signal.

Windshield Temperature and Inside Moisture Sensor

The windshield temperature and inside moisture sensor includes the relative humidity sensor, windshield temperature sensor and humidity sensing element temperature sensor.

This sensor assembly provides information about

  1. Relative humidity level at windshield (compartment side)
  2. Temperature of the windshield inside (compartment side)
  3. Temperature of the humidity sensor element

The relative humidity sensor measures the relative humidity of the compartment side of the windshield. It also detects the temperature of the windshield surface on the passenger compartment side. Both values are used as control inputs for the HVAC control module application to calculate the fog risk on windshield compartment side and ability to reduce fuel consumption by decreasing A/C compressor power to a minimum without causing any fog. The sensor will also enable partial recirculation mode in order to improve heat-up performance of the passenger compartment under cold ambient temperature conditions without the risk of mist build-up on the windshield. The humidity sensor element temperature sensor supplies the temperature of the humidity sensor element. It is only needed if the thermal contact between the humidity sensing element and the inside windshield surface is not sufficient.

Ambient Light/Sunload Sensor

The ambient light/sunload sensor includes the sunload sensor and passenger compartment temperature sensor.

This sensor assembly provides information about

  1. Sun heat intensity
  2. Elevation
  3. Azimuth
  4. Passenger compartment temperature

The sunload sensor is connected to ground and to a 12 V clocked power supply through the HVAC control module. This clocked power supply is to power the sensor electronics and to work as a clock generator to the sunload sensor micro controller. The sensor uses a pulse signal for data identification and transferring the sun intensity measurement. At each positive transition from the clocked supply input, the sunload sensor micro controller will shift channels enabling new intensity measurement on the signal output to the HVAC control module. The signal voltage varies between 0-4 V.

The passenger compartment temperature sensor is a negative temperature co-efficient thermistor. A signal and low reference circuit enables the sensor to operate. As the air temperature increases, the sensor resistance decreases. The sensor signal varies between 0-5 V.

Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Air Speed (Front)

The blower control switch is part of the Radio/HVAC control. The selected value of the blower switch position is sent to the HVAC control module via LIN-Bus.

The blower motor control module is an interface between HVAC control module and blower motor. The blower motor control module regulates supply voltage and ground circuits to blower motor. The HVAC control module provides a PWM signal to the blower motor control module in order to command the desired blower motor speed. The blower motor control module supplies battery voltage to the blower motor and uses the blower motor ground as a low side control to adjust the blower motor speed. The voltage amounts between 2-13 V and changes linear to the height of the PWM signal.

Air Speed - Rear (CJ4)

The blower control switches are part of the Radio/HVAC control - auxiliary. The selected value of the rear blower switches position is sent to the HVAC control module via LIN-Bus.

The blower motor control module - auxiliary is an interface between HVAC control module and blower motor - auxiliary. The blower motor control module - auxiliary regulates supply voltage and ground circuits to blower motor - auxiliary. The HVAC control module provides a PWM signal to the blower motor control module - auxiliary in order to command the desired blower motor speed. The blower motor control module - auxiliary supplies battery voltage to the blower motor - auxiliary and uses the blower motor - auxiliary ground as a low side control to adjust the blower motor speed. The voltage amounts between 2-13 V and changes linear to the height of the PWM signal.

Air Delivery (Front)

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

  1. Defrost
  2. Defog
  3. Panel
  4. Floor

The desired air distribution mode can be selected with the air distribution switches at the Radio/HVAC control. The Radio/HVAC control delivers the values to the HVAC control module via LIN-Bus. The HVAC control module controls the mode door actuator so that it drives the flap to the calculated position. Depending on the position of the flap, air is distributed through various ducts leading to the outlets in the dash. Turning the mode flap to the defrost position, the HVAC control module will move the recirculation actuator to outside air, reducing window fogging. When defrost is selected, the blower motor will be activated, regardless of the coolant temperature. The HVAC control module enables a high volume of air delivered to the front defrost vents. A/C is available in all modes.

The rear window defogger does not affect the HVAC system.

Air Delivery - Rear (CJ2)

Rear air delivery does not include an auxiliary blower, rear controls, or actuators such as Mode and Temperature. It uses only the vents in the console between and under the two front seats. The air temperature and mode from the rear ducts will match the temperature and mode that is chosen for the driver, and when air is directed to the windshield for defrost it will be blocked from the rear ducts.

Air Delivery - Rear (CJ4)

The HVAC control module controls the distribution of air by the mode door actuator - auxiliary. The modes that may be selected are

  1. AUTO
  2. Floor
  3. Bi-Level
  4. Vent

The desired rear air distribution mode can be selected with the Mode switch at the Radio/HVAC control - auxiliary. The Radio/HVAC control - auxiliary delivers the values to the HVAC control module via LIN-Bus. The HVAC control module controls the mode door actuator - auxiliary so that it drives the flap to the calculated position. Depending on the position of the flap, air is distributed through various ducts.

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 control module. The ambient air drawn through the HVAC control module absorbs the heat of the coolant flowing through the heater core. Heated air is distributed to the passenger compartment, through the HVAC control module, for passenger comfort. Opening or closing the air temperature flap controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and recirculates back to the engine cooling system.

A/C Cycle

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

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 fails 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 to the Receiver/Dehydrator(R/D).

The R/D contains desiccant that absorbs moisture that may be in the refrigerant system. The R/D also acts as a storage vessel to ensure that a steady flow of liquid reaches the thermal expansion valve. The refrigerant exits the R/D and flows through the liquid line to the thermal expansion valve.

The thermal expansion valve is located at the front of dash and attaches to the evaporator inlet and outlet pipes. The thermal expansion valve is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the thermal expansion valve, the pressure on the refrigerant is lowered. The thermal expansion valve also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the thermal expansion valve flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC control 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 A/C compressor, in a vapor state, and completing the A/C cycle of heat removal. At the A/C compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the HVAC control 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 control module as water.

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