HVAC Systems - Manual Chevrolet Cobalt I

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table (Ambient Air Temp Sensor )

Sensor Resistance Table (Ambient Air Temp Sensor )

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

HVAC Connector End Views

A/C Compressor Clutch (C67) Connector Part Information OEM: 12162017 Service: See Catalog 2-Way F Metri-Pack 150 Series Sealed (GY) Pin Wire Color Circuit No. Function A D-GN 59 A/C Compressor Clutch Supply Voltage (C67) B BK 150 Ground

A/C Refrigerant Pressure Sensor (L61) (C67) Connector Part Information OEM: 15397275 Service: See Catalog 3-Way F GT 150 Series Sealed (BK) Pin Wire Color Circuit No. Function 1 BK/WH 2751 Signal Ground 2 GY 2700 A/C Pressure Sensor 5-Volt Reference (C67) 3 OG/BK 380 A/C Refrigerant Pressure Sensor Signal (C67)

A/C Refrigerant Pressure Sensor (LSJ) (C67) Connector Part Information OEM: 15397275 Service: See Catalog 3-Way F GT 150 Series Sealed (BK) Pin Wire Color Circuit No. Function 1 BK 2751 Signal Ground 2 GY 2700 A/C Pressure Sensor 5-Volt Reference (C67) 3 RD/BK 380 A/C Refrigerant Pressure Sensor Signal (C67)

Air Temperature Actuator Connector Part Information OEM: 12064993 Service: See Catalog 6-Way F Micro-Pack 100 Series (BK) Pin Wire Color Circuit No. Function 5 PK 339 Run/Crank Ignition 1 Voltage 6 WH/BK 1236 Passenger Air Temperature Door Control 7 BK/WH 550 Ground 9 D-BU 1646 Passenger Air Temperature Door Position Signal 10 L-BU/BK 1688 5-Volt Reference

Blower Motor Connector Part Information OEM: 12064749 Service: See Catalog 2-Way F Metri-Pack 480 Series (BK) Pin Wire Color Circuit No. Function A OG 52 High Blower Motor Control B BN 141 Run Ignition 3 Voltage

Blower Motor Resistor Connector Part Information OEM: 12129566 Service: See Catalog 4-Way F Metri-Pack 280 Series Sealed (GY) Pin Wire Color Circuit No. Function A TN 63 Medium Blower Motor Control (1) B L-BU 72 Medium 2 Blower Motor Control C OG 52 High Blower Motor Control D YE 60 Low Blower Motor Control

HVAC Control Module C1 Connector Part Information OEM: 15416970 Service: See Catalog 16-Way F Micro 64 Modular (BK) Pin Wire Color Circuit No. Function 1 L-GN 2275 Mode 1 Valve Position Sensor Signal 2-3 - - Not Used 4 L-BU/BK 1688 5-Volt Reference 5 L-GN/BK 1647 Open Recirculation Door Control 6 PK/WH 1648 Close Recirculation Door Control 7 PK 339 Run/Crank Ignition 1 Voltage 8 PK 339 Run/Crank Ignition 1 Voltage 9 D-BU 1646 Passenger Air Temperature Door Position Signal 10 - - Not Used 11 D-GN 71 Off Blower Motor Control 12 L-BU/BK 1688 5-Volt Reference 13 WH/BK 1236 Passenger Air Temperature Door Control 14 TN 2273 Mode Door Control 15 BK/WH 550 Ground 16 BK/WH 550 Ground

HVAC Control Module C2 Connector Part Information OEM: 15406141 Service: See Catalog 8-Way F Micro 64 (BK) Pin Wire Color Circuit No. Function A1 PK 339 Run/Crank Ignition 1 Voltage A2 GY 8 Instrument Panel Lamp Supply Voltage (1) A3 - - Not Used A4 RD/WH 1540 Battery Positive Voltage A5 BK 550 Ground A6 L-GN 66 A/C Request Signal (C67) A7 WH 193 Rear Defog Relay Control A8 L-BU 292 Rear Defog Switch Signal

HVAC Control Module C3 Connector Part Information OEM: 12064998 Service: See Catalog 8-Way F Metri-Pack 280 Series (BK) Pin Wire Color Circuit No. Function A D-GN 71 Off Blower Motor Control B BK 550 Ground C-D - - Not Used E OG 52 High Blower Motor Control F L-BU 72 Medium 2 Blower Motor Control G TN 63 Medium Blower Motor Control (1) H YE 60 Low Blower Motor Control

Mode Actuator Connector Part Information OEM: 12064993 Service: See Catalog 6-Way F Micro-Pack 100 Series (BK) Pin Wire Color Circuit No. Function 5 PK 339 Run/Crank Ignition 1 Voltage 6 TN 2273 Mode Door Control 7 BK/WH 550 Ground 9 L-GN 2275 Mode 1 Valve Position Sensor Signal 10 L-BU/BK 1688 5-Volt Reference

Recirculation Actuator Connector Part Information OEM: 12059110 Service: See Catalog 2-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A L-GN/BK 1647 Open Recirculation Door Control B PK/WH 1648 Close Recirculation Door Control

Scan Tool Output Controls

ECM Scan Tool Output Controls

Scan Tool Data List

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

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

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

Scan Tool Data List

Scan Tool Data Definitions

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

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

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

The HVAC Scan Tool Data Definitions contains a brief description of all HVAC related parameters available on the scan tool. The list is in alphabetical order. A given parameter may appear in any one of the data lists. In some cases, the parameter may appear more than once or in more than one data list in order to group certain related parameters together.

Circuit Description

The body control module (BCM) monitors the outside air temperature sensor to display outside air temperature. The temperature sensor is a 2-wire negative temperature co-efficient thermistor. The BCM applies 5 volts to an internal input resistor that is connected to the signal circuits of the outside air temperature sensor. The BCM provides the ground to the outside air temperature sensor through the low reference circuit. The BCM monitors the voltage drop across the outside air temperature sensor and uses the input for automatic control calculations. When the outside air temperatures are cold, the resistance of the sensors are high, and the voltage signals are high. When the air temperatures are hot, the resistance of the sensors are low, and the voltage signals are low. The BCM converts the voltage value to a temperature value of Celsius and Fahrenheit to be displayed by the driver information center (DIC).

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B0158 Outside Air Temperature Sensor

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC B0158

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The BCM detects the sensor signal circuit is less than 0.4 volt or more than 4.8 volts.

Conditions Taken When the DTC Sets

1. The default value of 3°C (38°F) will be substituted for the outside air temperature sensor data by the BCM.
2. The DIC will display the set temperature when ON.

Conditions for Clearing the DTC

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

Test Description

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

1. 2: The operating range of the sensor is between 0.4-4.8 volts. If the DMM displays a value less than 0.4 volt, or greater than 4.8 volts, then the sensor is performing outside of its designed limits.
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.
4. 5: This step tests the signal circuit for a short to ground.
5. 6: This step tests the signal circuit for a short to voltage, a high resistance, or an open.
6. 7: This step tests the low reference circuit for a high resistance or an open.

DTC B0158

The engine control module (ECM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The ECM supplies a 5-volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the A/C refrigerant pressure sensor signal to the ECM to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM commands the cooling fans ON. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC P0532 (A/C) Air Conditioning Pressure Sensor Circuit Low Voltage
2. DTC P0533 (A/C) Air Conditioning Pressure Sensor Circuit High Voltage

1. The engine is running.
2. Any of the conditions for setting the DTC are met for 15 seconds.

1. The ECM detects that the A/C pressure is less than 0 psi (0.20 volt).
2. The ECM detects that the A/C pressure is more than 428 psi (4.92 volts).

Action Taken When the DTC Sets

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM stores the Failure Records.
3. The A/C compressor clutch is disabled.

1. The history DTC will clear after 40 consecutive ignition cycles have occurred without a malfunction.
2. The DTC can be cleared by using the scan tool.
3. The DTC will become history if the ECM no longer detects a failure.

Diagnostic Aids

Test the following conditions

1. Visually inspect the sensor for contamination or damage.
2. Inspect for the following that may affect the sensors accuracy: A malfunction within the refrigerant system causing high pressure Visually inspect the A/C components and lines for damage.
3. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/cobalt/i-2004-2010/remont/electrical-component-locations/#wiring-systems-electrical-power-management__testing-for-intermittent-conditions-and-poor) in Wiring Systems.

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

1. 4: This step tests for the proper operation of the circuit in the low voltage range.
2. 5: 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. 6: This step tests for a short to voltage in the 5-volt reference circuit.
4. 7: This step tests for a high resistance or an open in the low reference circuit.

DTC P0532 or P0533

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/chevrolet/cobalt/i-2004-2010/remont/electrical-component-locations/#wiring-systems-electrical-power-management__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__air-temperature-description-and-operation) .
5. The following could cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
6. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

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

Symptom List

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

1. «HVAC Compressor Clutch Does Not Engage»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual)
2. «HVAC Compressor Clutch Does Not Disengage»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__hvac-compressor-clutch-does-not-disengage)
3. «Blower Motor Always On»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__blower-motor-always-on)
4. «Blower Motor Inoperative»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__blower-motor-malfunction)
6. «Too Hot in Vehicle»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual)
7. «Too Cold in Vehicle»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual)
8. «Air Delivery Improper»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual)
9. «Leak Testing»(/chevrolet/cobalt/i-2004-2010/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__leak-testing) in Heating, Ventilation and Air Conditioning
10. «Defrosting Insufficient»(/chevrolet/cobalt/i-2004-2010/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__defrosting-insufficient) in Heating, Ventilation and Air Conditioning
11. «Noise Diagnosis - HVAC Module»(/chevrolet/cobalt/i-2004-2010/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module) in Heating, Ventilation and Air Conditioning
12. «Odor Diagnosis»(/chevrolet/cobalt/i-2004-2010/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis) in Heating, Ventilation and Air Conditioning

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

1. 2: The A/C compressor relay output is disabled if engine coolant temperature is above 123°C (253°F). The instrument panel engine coolant gage will indicate overheating.

1. 3: Place the mode switch in any position except OFF, and place the air temperature control switch in a cold setting. Use the bi-level mode for consistent testing of the A/C system operation.
2. 6: The HVAC control assembly is inoperative if the assembly does not respond to any operator control requests.

1. 14: Be sure to verify the engine control module (ECM) engine grounds are secure and clean.

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Disengage

HVAC Compressor Clutch Does Not Disengage

Blower Motor Always On

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

Blower Motor Malfunction

Blower Motor Malfunction

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

1. 4: The HVAC control module is inoperative when the module does not respond to an operator control request.
2. 5: If the condition does not occur when an air conditioning (A/C) request has been made then you must bypass the A/C performance test procedures.
3. 6: These actions are the enable criteria for the A/C compressor to operate. Ambient air temperature must be above 3°C (38°F) in order for this A/C compressor test to be run.
4. 7: Performing the Air Conditioning System Performance Test ensures that the A/C system is operating properly for further testing.
5. 9: If no condition found with all conditions listed then compare door travel to known good vehicle.
6. 15: The voltage will vary between 0-5 volts during normal operation. Ensure to observe the air temperature actuator driveshaft and the volt meter when jumping the control circuit with 5-volt reference and the ground circuits. The air temperature actuator and the HVAC control assembly connectors must be connected during this step.

Too Hot in Vehicle

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

1. 4: The HVAC control assembly is inoperative when the assembly does not respond to an operator control request.
2. 8: If no condition found with all conditions listed then compare door travel to known good vehicle.
3. 14: The voltage will vary between 0-5 volts during normal operation. Ensure to observe the air temperature actuator driveshaft and the volt meter when jumping the control circuit with 5-volt reference and the ground circuits. The air temperature actuator and the HVAC control assembly connectors must be connected during this step.

Too Cold in Vehicle

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

1. 3: This step tests for a blower motor that does not operate regardless of the desired blower motor speed.
2. 4: This step tests for a blower motor that operates, yet does not accurately respond to the desired blower motor speed.
3. 5: This step verifies that there is power to the HVAC control assembly.
4. 13: The voltage will vary between 0-5 volts during normal operation. The HVAC control assembly connector must be connected during this step.

Air Delivery Improper

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

1. 6: The HVAC control assembly is supplied by 2 voltage circuits. Test both voltage circuits.

Air Recirculation Malfunction

Removal Procedure

1. Remove the I/P center trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Center»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.
2. Remove the HVAC control module assembly screws.
3. Remove the HVAC control module assembly.
4. Disconnect the HVAC control module assembly electrical connectors.

Installation Procedure

1. Connect the HVAC control module assembly electrical connectors.
2. Install the HVAC control module assembly.
3. Install the HVAC control module screws. Tighten: Tighten the screws to 2.2 N.m (19 lb in).
4. Install the I/P center trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Center»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.

1. Remove the fuse labeled HVAC CTRL (BATT).
2. Remove the steering column filler panel. Refer to «Steering Column Filler Replacement»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
3. Disconnect the air temperature actuator electrical connector.
4. Remove the air temperature actuator screws.
5. Remove the air temperature actuator.

1. Install the air temperature actuator.
2. Install the air temperature actuator screws. Tighten: Tighten the screws to 2.2 N.m (19 lb in).
3. Install the air temperature actuator electrical connector.
4. Install the steering column filler panel. Refer to «Steering Column Filler Replacement»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
5. Install the fuse labeled HVAC CTRL (BATT).
6. Start the engine and let run for one minute.

1. Remove the air temperature actuator. Refer to «Air Temperature Actuator Replacement»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual) .
2. Disconnect the mode actuator electrical connector.
3. Remove the mode actuator assembly screws.
4. Remove the mode actuator assembly.

1. Install the mode actuator assembly.
2. Install the mode actuator assembly screws. Tighten: Tighten the screws to 2.2 N.m (19 lb in).
3. Install the mode actuator electrical connector.
4. Install the air temperature actuator. Refer to «Air Temperature Actuator Replacement»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual) .
5. Start the engine and let run for one minute.

1. Remove the fuse labeled HVAC CTRL (BATT).
2. Remove the I/P retainer. Refer to «Instrument Panel (I/P) Retainer Replacement»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel Gages and Console.
3. Disconnect the recirculation actuator electrical connector.
4. Remove the recirculation actuator screw.
5. Remove the recirculation actuator.

1. Install the recirculation actuator.
2. Install the recirculation actuator screw. Tighten: Tighten the screw to 2.2 N.m (19 lb in).
3. Install the recirculation electrical connector.
4. Install the I/P retainer. Refer to «Instrument Panel (I/P) Retainer Replacement»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel Gages and Console.
5. Install the fuse labeled HVAC CTRL (BATT).
6. Start the engine and let run for one minute.

Air Delivery Description and Operation

The air delivery description and operation is divided into 4 areas

1. HVAC Control Components
2. Air Speed
3. Air Distribution
4. Recirculation Operation

HVAC Control Assembly

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 3 voltage circuits provide power to the control assembly. The control assembly 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 assembly 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 HVAC control assembly 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 HVAC control assembly. Once the position signal and the commanded value are the same, the HVAC control assembly changes the control signal to 2.5 volts.

Air Speed

The HVAC control assembly applies ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

1. Low speed, 3 resistors
2. Medium 1 speed, 2 resistors
3. Medium 2 speed, 1 resistors

When the operator requests High speed, the HVAC control assembly applies ground directly to the blower motor.

OFF mode

When the OFF position is selected, the HVAC control module applies ground to the fan off input within the HVAC control assembly through the off blower motor control circuit. When the HVAC control assembly receives this input, any A/C request will be cancelled and the A/C request LED will turn OFF.

Air Distribution

The HVAC control assembly controls the mode actuators in order to distribute airflow to a desired outlet. When the mode door is moved to the mix-blend or defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. Regardless of the mode setting, a small amount of air will be diverted to the defrost ducts to reduce windshield fogging. On startup, the HVAC control assembly will place the mode door in the last selected position.

Recirculation Operation

The recirculation actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either ground or a 12-volt value to coordinate the actuator movement. The HVAC control assembly reverses the polarity of the control circuits to move the actuator in the opposite direction. The recirculation operation can function with blower motor in either the ON or OFF position. The A/C compressor automatically comes ON when recirculation is selected. Recirculation is not available in Defrost and Mix-Blend mode.

Air Temperature Description and Operation

The air temperature controls are divided into 4 areas

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

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive and ignition 3 voltage circuits provide power to the assembly. The control assembly 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.

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 engine control module (ECM) 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 or low pressure condition exists. The ECM disables the compressor clutch under the following conditions

A/C pressure is more than 2,951 kPa (428 psi). The clutch will be enabled after the pressure decreases to less than 2,068 kPa (300 psi). A/C high side pressure is less than 310 kPa (44 psi). The clutch will be enabled after the A/C high side pressure increases to more than 310 kPa (44 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 to the A/C compressor or cause evaporator icing. The HVAC control module applies 12 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 124 kPa (18 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40 psi). This enables the A/C compressor to turn back ON.

Heating and A/C Operation

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

1. Recirculation
2. Difference between inside and desired temperature
3. Difference between ambient and desired temperature
4. Blower motor speed setting
5. Mode setting

The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the temperature setting.

The ECM will operate the A/C system automatically in FRONT DEFROST mode to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system maybe running without the A/C LED indicator illuminated when in FRONT DEFROST mode. The following conditions must be met in order for the ECM to turn ON the compressor clutch

1. Body control module (BCM) Battery voltage is between 9-16 volts. A/C request from the HVAC control assembly
2. ECM Engine coolant temperature (ECT) is less than 123°C (253°F). Engine speed is less than 5,300 RPM. Engine speed is more than 600 RPM. A/C high side pressure is between 2951-310 kPa (428-44 psi).

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

1. Throttle position is 100 percent for 10 seconds.
2. A/C high side pressure is more than 2951 kPa (428 psi) and will reengage once the pressure drops below 2068 kPa (300 psi).
3. A/C high side pressure is less than 310 kPa (44 psi).
4. ECT is more than 123°C (253°F).
5. Engine speed is less than 475 RPM.
6. Engine speed is more than 6,000 RPM.
7. ECM detects excessive torque load.
8. ECM detects insufficient idle quality.

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

Engine Coolant

Engine coolant is the key element of the heating system. The thermostat controls 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 heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort.

The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module air temperature door. The coolant exits the heater core through the return heater hose and is recirculated back through the engine cooling system.

A/C Cycle

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

The Delphi model CVC6 piston type compressor is used on this model year vehicle. The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure 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 high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

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 thermal expansion valve (TXV).

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

Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant 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.

Special Tools

Special Tools Illustration Tool Number/Description J 43600 ACR2000 Air Conditioning Service Center J 43907 Connector Test Adapter Kit 7000081 Tech 2 Kit

Scheme 7

Scheme 8

Scheme 9

See also:
• DTC Symptom Description
• Diagnostic System Check - Vehicle
• Testing for Intermittent Conditions and Poor Connections
• Circuit Testing
• Wiring Repairs
• Connector Repairs
• Ambient Air Temperature Gage Sensor Replacement
• Control Module References
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Checking Aftermarket Accessories
• Leak Testing
• Defrosting Insufficient
• Noise Diagnosis - HVAC Module
• Odor Diagnosis
• Engine Overheating
• Air Conditioning (A/C) System Performance Test (L61)
• Compressor Clutch Assembly Replacement
• Compressor Replacement (2.2L (L61))
• Compressor Replacement (2.0L (LSJ))
• Heating Performance Diagnostic
• Fastener Notice
• HVAC Schematics
• HVAC Connector End Views
• HVAC Compressor Clutch Does Not Disengage
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• Blower Motor Always On
• Blower Motor Inoperative
• Blower Motor Malfunction