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HVAC System - Automatic: Other GMC Sierra III

Automatic HVAC System ~4779 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

Scan Tool Reference

Control Module References

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Ignition ON.
  2. Verify DTC B0173, B0178, B0509, B0514, or B3933, is not set. If only one of the DTCs is set Refer to Circuit/System Testing. If more than one of the DTCs is set Repair or replace the temperature sensor harness. If none of the DTCs is set
  3. Verify, with a thermometer, the temperature sensors are accurate within 4°C (8°F) If only one of the temperature sensors are not accurate Refer to Circuit/System Testing. If more than one of the temperature sensors are not accurate Repair or replace the temperature sensor harness. If the temperature sensors are accurate
  4. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

Scan Tool Reference

Control Module References for scan tool information

  1. Perform the «Actuator Recalibration»(ref-651050-S22056372462014081900000) procedure.
  2. Verify the concern or DTC has been corrected. If the concern or DTC has not been corrected Verify DTC B1395 is not set. If DTC B1395 is set Refer to Circuit/System Testing - DTC B1395. If DTC B1395 is not set Refer to Circuit/System Testing - DTC B0228, B0413, B0423 or B374A.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) for HVAC control module replacement, programming and setup

Schematic Reference

Instrument Cluster 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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 Ambient Air Temperature parameter is between -39°C (-38°F) and +88°C (+190°F) and changes with air temperature changes. If not between -39°C (-38°F) and +88°C (+190°F) or changes with air temperature changes Refer to Circuit/System Testing. If between -39°C (-38°F) and +88°C (+190°F) and changes with air temperature changes
  3. Perform the HVAC Ambient Air Temperature Instant Update special function with the scan tool
  4. Verify the scan tool Ambient Air Temperature displayed is within five degrees of actual ambient air temperature. If not within five degrees of actual ambient air temperature Refer to Circuit/System Testing. If within five degrees of actual ambient air temperature
  5. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) for ECM 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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 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-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) for engine control module replacement, programming and setup

Symptoms - HVAC Systems - Automatic

Note. The following steps must be completed before using the symptom tables

  1. Perform the «Diagnostic System Check - Vehicle»(ref-650999-S38140870152014081900000) before using the HVAC System Malfunction procedure 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 «Automatic HVAC Description and Operation»(ref-651050-S02465645112014081900000) .

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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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 the scan tool Blower Motor Switch parameter changes when rotating the blower switch through each speed position. If the parameter does not change for each speed position Replace the A26 HVAC Controls. If the parameter changes for each speed position
  3. Verify the blower motor operates properly with the blower motor switch in each speed position. If the blower motor does not operate in each speed position Refer to «DTC B0193»(ref-651050-S01504640482014081900000) . If the blower motor operates properly in each speed position
  4. Verify the scan tool parameters listed below change when pressing the appropriate switch. Driver Temp. Dr. Motor Command Psgr. Temp. Dr. Motor Command Recirculation Dr. Motor Command Mode Dr. Motor Command If any parameter does not change Replace the A26 HVAC Controls If all parameters change
  5. Verify the HVAC doors listed below move when pressing the appropriate switch. Driver Temperature Passenger Temperature Mode Recirculation If any HVAC door does not move Refer to «DTC B0228, B0413, B0423, B1395, or B374A»(ref-651050-S19310876382014081900000) . If all HVAC doors move
  6. Install the J43600 ACR Air Conditioning Service Center.
  7. Verify the high side pressure reading on the Air Conditioning Service Center is within 10% of the scan tool A/C High Side Pressure Sensor parameter. If the reading is not within 10% Refer to «DTC P0532 or P0533»(ref-651050-S07720271462014081900000) . If the reading is within 10%
  8. 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 (LV3)»(ref-651014-S31335754272014081900000) , «Air Conditioning (A/C) System Performance Test (L83)»(ref-651014-S18082034132014081900000) If the reading is between 269-2929 kPa (39-425 PSI)
  9. 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 If not within 10% of ambient temperature Refer to «DTC B0173, B0178, B0509, B0514 or B3933»(ref-651050-S23749440382014081900000) . If within 10% of ambient temperature
  10. Engine ON, A/C system ON
  11. 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-651050-S04069731692014081900000) . If the Q2 A/C Compressor Clutch is engaged, refer to «Air Conditioning (A/C) System Performance Test (LV3)»(ref-651014-S31335754272014081900000) , «Air Conditioning (A/C) System Performance Test (L83)»(ref-651014-S18082034132014081900000) and «DTC B393B»(ref-651050-S37006596532014081900000) . If the air is cool
  12. 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-651014-S35001924982014081900000) . If the air is warm
  13. Engine OFF, ignition ON.
  14. Verify the Sunload parameter changes while covering the B10B Ambient Light/Sunload Sensor with a shop towel or other suitable item. If the Sunload parameter does not change Refer to «DTC B0183»(ref-651050-S32818742212014081900000) . If the Sunload parameter changes
  15. 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»(ref-651050-S41228934832014081900000) . If less than a 3°C (5°F) difference
  16. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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-651023-S06735791342014081900000)
  2. «Connector Repairs»(ref-651023-S36930316752014081900000)
  3. «Testing for Intermittent Conditions and Poor Connections»(ref-651023-S31795657182014081900000)
  4. «Wiring Repairs»(ref-651023-S35699655412014081900000)

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 Switch 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-651050-S37083471152014081900000) 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-651050-S37006596532014081900000) If the parameter does change
  9. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

  1. «HVAC Component Replacement Reference»(ref-651050-S27355274792014081900000)
  2. «Control Module References»(ref-651024-S37773196412014081900000) 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

HVAC Control

The HVAC control contains all switches, buttons and dials which are required to control the functions of the HVAC system 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

The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. The five circuits are low reference, 5 V reference, actuator position signal and two control circuits. The actuator control circuits use either a ground or 5 V signal to command the actuator movement. When the actuator is at rest, both control circuit voltage values are 2.5 V. To operate the actuator, the HVAC control module supplies 5 V on one control circuit and ground on the other control circuit. Reversing the polarity results in the actuator moving in the opposite direction. When the actuator shaft rotates, the potentiometers sliding contact changes the door position signal between 0-5 volts. The door position signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index the actuator position. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 V 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 both control signals to 2.5 V.

Air Temperature Actuators

The air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. The five circuits are low reference, 5 V reference, actuator position signal and two control circuits. The actuator control circuits use either a ground or 5 V signal to command the actuator movement. When the actuator is at rest, both control circuit voltage values are 2.5 V. To operate the actuator, the HVAC control module supplies 5 V on one control circuit and ground on the other control circuit. Reversing the polarity results in the actuator moving in the opposite direction. When the actuator shaft rotates, the potentiometers sliding contact changes the door position signal between 0-5 volts. The door position signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index the actuator position. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 V 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 both control signals to 2.5 V.

Recirculation Actuator

The recirculation actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. The five circuits are low reference, 5 V reference, actuator position signal and two control circuits. The actuator control circuits use either a ground or 5 V signal to command the actuator movement. When the actuator is at rest, both control circuit voltage values are 2.5 V. To operate the actuator, the HVAC control module supplies 5 V on one control circuit and ground on the other control circuit. Reversing the polarity results in the actuator moving in the opposite direction. When the actuator shaft rotates, the potentiometers sliding contact changes the door position signal between 0-5 volts. The door position signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index signal voltage is converted to a 0-255 count range. The HVAC control module uses a range of 0-255 counts to index the actuator position. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 V 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 both control signals to 2.5 V.

Blower Motor

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control from the HVAC control module, battery positive and ground circuits enable the blower motor control module to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower motor control module in order to command the blower motor speed. The blower motor control module transfers the PWM signal into a corresponding blower motor voltage.

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 adjust the mixed air flap position according to the requested temperature.

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 evaporator icing.

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 uses a conventional belt driven magnetic clutch to engage and mechanically turn the compressor. When the A/C switch is pressed, the HVAC control module sends an A/C request message to the ECM via serial data. If specific criteria is met, the ECM then grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the permanently grounded A/C compressor clutch. The A/C compressor clutch will then be activated.

This A/C system utilizes a variable displacement solenoid valve to alter the amount of displacement created by the turning of the compressor. The HVAC control module provides both battery voltage and a pulse width modulated ground to the variable displacement solenoid valve. When the A/C switch is pressed, the HVAC control module grounds the variable displacement solenoid using a (PWM) signal in order to determine the amount of compressor displacement. The performance of the A/C compressor is regulated based on cooling load.

Ambient Light/Sunload Sensor

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

The blower control switch is part of the HVAC controls. The selected value of the blower switch position is sent to the HVAC control module via LIN-Bus. The blower motor control circuitry is integrated within the blower motor assembly. The HVAC control module provides a low side pulse width modulation (PWM) signal to the blower motor to request a specific motor speed. The blower motor translates the PWM signal and drives the motor accordingly.

Afterblow

Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned OFF. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned ON. If the afterblow feature is required due to an odor concern, it must be enabled using the scan tool Afterblow configuration function.

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate

  1. The engine has been turned OFF for at least 30 minutes.
  2. The ambient air temperature is at least 21°C (70°F).
  3. The A/C compressor operated for more than 2 minutes before shut down.
  4. The system voltage is at least 12 volts.

Once the above conditions have been met, the blower motor will perform the following sequence 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.

Air Delivery

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 HVAC control. The 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.

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. There are currently two approved Environmental Protection Agency refrigerants. They are R134a and R-1234yf and either one could be used in this vehicle. R-1234yf is a newly EPA approved refrigerant and it will require the use of an updated Air Conditioning Refrigerant Recovery/Recharge Cart/System. Refer to Refrigerant Recovery and Recharging for correct tool usage. Both refrigerants are very low temperature gases 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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