HVAC System - Automatic: Other Cadillac STS I facelift

Sensor Resistance Table

Scheme 22

Scheme 23

Scheme 24

Scheme 25

Scheme 26

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Outside Air Quality Sensor Replacement»(ref-338123-S13547102272009081700000)
2. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, observe the appropriate air temperature sensor. The reading should be between -35°C (-39°F) and 85°C (185°F) and change with air temperature changes.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Ambient Air Temperature Sensor Replacement»(ref-338123-S20709481162009081700000)
2. «Inside Air Temperature Sensor Replacement»(ref-338123-S17217520852009081700000)
3. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the appropriate scan tool Sunload Sensor parameter. The reading should be between 5 and 250 counts and change with sunlight intensity.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Sun Load Temperature Sensor Replacement»(ref-338123-S15846499792009081700000)
2. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the appropriate actuator to 100 percent with a scan tool. The scan tool should display between 224 and 230 counts on the mode actuator, all other actuators should display between 199 and 205 counts.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Recirculation Actuator Replacement»(ref-338123-S42584227992009081700000)
2. «Mode Actuator Replacement»(ref-338123-S20976347242009081700000)
3. «Temperature Valve Actuator Replacement - Left Side»(ref-338123-S38536093592009081700000)
4. «Temperature Valve Actuator Replacement - Right Side»(ref-338123-S04035793792009081700000)
5. «Auxiliary Temperature Valve Actuator Replacement»(ref-338123-S03061102522009081700000)
6. «Mode Actuator Replacement - Console»(ref-338123-S11496802582009081700000)
7. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Outside Air Quality Sensor Replacement»(ref-338123-S13547102272009081700000)
2. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C Evaporator Temperature Sensor parameter. The reading should be between -35°C (-39°F) and 98°C (208°F) and change with evaporator temperature changes.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C High Side Pressure Sensor parameter. The reading should be between 1 psi and 428 psi.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement»(ref-338121-S36282835482009081700000)
2. «Control Module References»(ref-338152-S12253781062009081700000) for ECM replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM setup, replacement, and programming

Symptoms - HVAC Systems - Automatic

1. Perform the «Diagnostic System Check - Vehicle»(ref-338149-S41903538652009081700000) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Automatic HVAC Description and Operation»(ref-338123-S03480481472009081700000)

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

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

Engine running, press the A/C request switch. The A/C compressor clutch should engage.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement (LY7)»(ref-338121-S12271937792009081700000) or «Air Conditioning Compressor Replacement (LH2)»(ref-338121-S09911290062009081700000)
2. «Compressor Relay Replacement»(ref-338121-S16440763102009081700000)
3. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module and ECM replacement, setup, and programming

Blower Controller

The blower control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower controller in order to command the blower motor speed. The control processor uses the blower motor ground or low reference as a low side control to adjust the blower motor speed.

Air Speed

The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motors speed by placing the blower knob dial in a desired speed position or by selecting automatic operation. In manual operation, the blower has 6 speed selections. The HVAC control module may alter the blower motor speed due to compensating factors. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. In manual and automatic operation, the blower speed temporarily reduces speed during transition between outlet modes.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, switch the Climate Control System to the manual setting. Press the fan speed control button from the lowest to highest setting. The blower motor speed should change between commanded states.
2. Press the power button located on the drivers side of the climate control panel to turn the entire climate control system ON or OFF. The blower motor should turn OFF.

Blower Relay

1. Ignition OFF, disconnect the BLOWER relay.
2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
4. Test for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the relay.
5. Install a 40A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Blower Motor

1. Ignition OFF, disconnect the harness at the blower motor.
2. Install a 40A fused jumper wire between circuit terminal 1 and 12 volts. Install a jumper wire between the low reference circuit terminal 2 and ground. Verify the blower motor activates. If the blower motor does not activate, replace the blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Blower Motor Replacement»(ref-338121-S06952801332009081700000)
2. «Control Module References»(ref-338152-S12253781062009081700000) for blower controller and HVAC control module replacement, setup, and programming

Evaporator, Inside and Ambient Air Temperature Sensors

The HVAC control module supplies the evaporator, inside and ambient air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensors, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-338151-S30248766082009081700000)
2. «Connector Repairs»(ref-338151-S41110648952009081700000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-338151-S41477264612009081700000)
4. «Wiring Repairs»(ref-338151-S09708660722009081700000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. Verify the scan tool Right Sunload Sensor and Left Sunload Sensor parameters are within 3 counts of each other. If not within the specified range, refer to «Circuit/System Testing»(ref-338123-S00757523082009081700000) , under Sunload Sensor Circuit Malfunction.
2. Measure actual outside air temperature using a thermometer. Compare this value to the scan tool Outside Air Temp. Raw parameter. The measured temperature should be within 5 degrees of the parameter. If not within the specified range, refer to «Circuit/System Testing»(ref-338123-S00757523082009081700000) , under Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.
3. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of the parameter. If not within the specified range, «Circuit/System Testing»(ref-338123-S00757523082009081700000) , under Inside Air Temperature Sensor Circuit Malfunction.
4. Measure actual evaporator air temperature using a thermometer. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter. If not within the specified range, refer to «Circuit/System Testing»(ref-338123-S00757523082009081700000) , under Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Ambient Air Temperature Sensor Replacement»(ref-338123-S20709481162009081700000)
2. «Inside Air Temperature Sensor Replacement»(ref-338123-S17217520852009081700000)
3. «Sun Load Temperature Sensor Replacement»(ref-338123-S15846499792009081700000)
4. «Control Module References»(ref-338152-S12253781062009081700000) for HVAC control module replacement, setup, and programming

Afterblow Enabling

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 turned on by reprogramming the HVAC control module, refer to Service Programming System (SPS) .

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.
4. The system voltage is at least 12 volts.

Once the above conditions have been met, the following sequence of events will occur

1. The blower motor will run for 20 seconds.
2. The blower motor will be off for 10 minutes.
3. The blower motor will run for and additional 20 seconds.

HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). The instrument panel module (IPM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Remote Start and Personalization

If the remote start personalization feature for climate control is selected through radio, the HVAC control module will receive information that defines the current driver of the vehicle from the Ezkey module through GMLAN communication. This information shall be stored inside the HVAC control module memory. When a different key fob is selected, the HVAC control module will recall the appropriate driver settings. The full auto mode and previous set temp will be commanded if ambient air temperature is above 0°C (32°F). Defrost mode will be commanded when the ambient air temperature is below 0°C (32°F). Upon a battery reset, the HVAC control module shall also set the driver ID to Driver#1. The HVAC system will memorize the following system configurations for up to 2 unique drivers

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

If the remote start personalization feature for heated and vented seat control is selected through radio, if the inside air temperature is below 12°C (54°F) the heated seat will be commanded to high. If the inside air temperature is above 26°C (80°F) and the ambient air temperature is above 21°C (70°F) the vented seat will be commanded to high. When the HVAC control module is first turned On or key On, the last stored settings for the current driver will be activated, heat/vented seat control is carried over from remote start.

OnStar® Blower Control ON/OFF

During OnStar® audio control ON, the HVAC control module receives signals from OnStar® to reduce blower level to a level 4. OnStar® blower control becomes active in auto or manual blower operation. During this OnStar® blower control, if in manual or auto blower, the display will show AUTO for blower display. This blower reduction is to ensure that all incoming and outgoing voice calls will be recognized by the OnStar® module. The driver is allowed to override the OnStar® auto blower level by increasing or decreasing it manually to any desired level. When OnStar® no longer sends the request for blower control the HVAC control module will cancel OnStar® blower control and resume previous blower level if no manual override of the blower was selected.

All Air Temperature, Recirculation and Mode Actuators

The actuators are 5-wire bi-directional electric motors that incorporate a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, one of the control circuits is grounded. 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 removes power and ground from the control circuits.

Air Temperature Sensors

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

1. Ambient
2. Inside

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal decreases as the resistance decreases. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

The inside temperature sensor operates within a temperature range between -6.5 to +57.5°C (+20.3 to +135.5°F). If the sensor is shorted to ground, voltage, or an open, the system will operate using an estimated default value to allow the system to operate. The ambient sensor operates within a temperature range between -30 to +51°C (-22 to +123.8°F). If the HVAC control module has determined that the ambient temperature sensor has failed, the driver information center (DIC) display shall display - - - - in place of the outside air temperature. If the sensor is shorted to ground, voltage, or an open, the system will operate using an estimated default value to allow the system to operate. If the engine coolant temperature is not more than 3°C (5.4°F) above the sensor reading, or if the engine has not been started in 3 hours, then the actual ambient air temperature sensor reading is displayed. Also at vehicle speeds greater than 35 km/h (22 mph), the ambient air temperature displayed may be allowed to increase, but only at a slow, filtered rate. The DIC displays the ambient air temperature value that it receives from the HVAC control module through a GMLAN message. The ambient air temperature value can be updated by an outside air instant update feature.

To use this feature, press the following switches on the HVAC control module simultaneously

1. AUTO
2. A/C OFF
3. REAR DEFOGGER

Sunload Sensor

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicle's inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If the sensor is open or shorted, no sunload adjustment occurs and the SERVICE A/C SYSTEM message is displayed.

Evaporator Temperature Sensor

The HVAC control module monitors the temperature of the air passing through the evaporator by the A/C evaporator air temperature sensor. This sensor is located on the evaporator core. The temperature is used to cycle the A/C compressor ON and OFF to prevent the evaporator core from freezing. A thermistor inside the sensor varies its resistance to monitor the evaporator temperature. The HVAC control module monitors the voltage drop across the thermistor when supplied with a 5-volt reference signal. The HVAC control module will send a serial data message to the engine control module (ECM) to stop requesting the A/C compressor clutch operation if the temperature drops below 3°C (37°F). The sensor must be above 4°C (39°F) to request the A/C compressor clutch again.

The sensor operates within a temperature range between -40 to +215°C (-40 to +355°F). If the HVAC control module detects an open in the evaporator temperature sensor or circuit, the serial data message sent to the ECM will not submit the A/C ON request. The HVAC control module will then send a request to the radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

The A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists.

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the serial data message sent to the HVAC control module will be invalid. The HVAC control module will then send a request to the radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant, until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur

1. The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur

1. The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

Blower Motor Relay

The blower motor relay provides a supply voltage to the blower motor and blower motor control processor. The HVAC control module commands the blower motor relay ON anytime the commanded blower speed is not OFF.

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, blower motor supply voltage and ground circuits enable the control processor to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

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 turned ON by reprogramming the HVAC control module. Refer to Control Module References .

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 following sequence of events will occur

1. The blower motor will RUN for 20 seconds.
2. The blower motor will be OFF for 10 minutes.
3. The blower motor will RUN for and additional 20 seconds.

Air Distribution

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. The mode switch provides the vehicle operator with the ability to override the automatic setting. When the mode door is moved to the defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

Recirculation

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in defrost. When the mode is in defog, recirculation will only be available for 10 minutes. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

Air Quality Sensor (RPO K14)

Warning - The air quality sensor recognizes carbon monoxide but is not designed as a safety feature to protect you from carbon monoxide. The air quality sensor is designed to limit your exposure to gasoline exhaust fumes and or diesel exhaust fumes that could enter into the passenger compartment from nearby vehicles for a limited amount of time.

The HVAC control module monitors the outside air quality while in AUTO mode via the air quality sensor assembly. You can activate the air quality sensor on your vehicle, if equipped, by pressing the Auto button on the HVAC module. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuit, and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor that is used for detecting gasoline exhaust fumes and a Nox sensor that is used for detecting nitrous oxide, diesel exhaust fumes. The HVAC control module outputs a 5-volt signal on the HC and Nox control circuits and operates in a range between 0-5 volts.

The HVAC module updates the air quality sensor calibration approximately 4 times per second. The air quality sensor input to the HVAC module is compared to the previously updated air quality sensor calibration. If the voltage difference is great enough the recirc actuator will be controlled to recirc, outside air, or partial recirc outside air position based on the air quality sensor input.

When air quality around the front of the vehicle is poor, the air quality sensor system operates as follows

1. Poor air quality with high HC levels will cause the HC control circuit to read a lower voltage.
2. Poor air quality with high Nox levels will cause the Nox control circuit to read a higher voltage.
3. The recirculation actuator is forced to the recirculation position.
4. The recirc symbol on the HVAC module will illuminate.
5. The recirc icon will not illuminate if the recirc actuator is already in the auto recirc position.

When air quality around the front of the vehicle is normal, the air quality sensor system operates as follows

1. Normal air quality levels the HC control circuit will recognize very little voltage change from the previously updated calibration.
2. Normal air quality levels the Nox control circuit will recognize very little voltage change from the previously updated calibration.
3. The recirculation actuator position is not controlled by the air quality sensor system.

The following are conditions that will prevent the air quality sensor from controlling the recirc actuator

1. A/C OFF conditions (compressor OFF) prevents air quality sensor from changing the current position of the actuator)
2. Coolant temperature below 37°C (99°F) during warm up will prevent the blower from operating and air quality sensor from controlling the recirc position.
3. Outside air temperature less than 5°C (41°F) (prevents air quality sensor from changing the current position of the actuator)
4. Outside air temperature less than 15°C (59°F) and A/C high side pressure less than 196 kpa (28 psi) (prevents air quality sensor from changing the current position of the actuator)
5. 28 seconds sensor warm-up time after ignition is turned ON (prevents air quality sensor from changing the current position of the actuator)
6. Evaporator temperature sensor failure
7. Customer manually selects defrost or defog (forces actuator to outside air position)
8. Customer manually selects recirc or outside air position
9. Coolant temperature above 112°C (V8), 119°C (HFV6) the actuator is forced to the recirc position. When coolant temperature drops below 109°C (V8), 116°C (HFV6) forced recirc is canceled.
10. A/C pressure above 2 500 KPA (362 psi) the actuator is forces to the recirc position. When A/C pressure drops below 2 000 KPA (290 psi) forced recirc is canceled.

The following describes the recirc actuator function after the air quality sensor has canceled the command to recirc

1. Full recirc position will be held for 2 minutes when vehicle speed is less than 10 km/h (6.3 mph) after 2 minutes expires the recirc door will move to full outside air position.
2. Partial recirc, outside air position will be held for 2 minutes when vehicle speed is above 20 km/h (12.5 mph) after 2 minutes expires the recirc door will move to full outside air position.
3. Full outside air position if vehicle speed is greater than 60 km/h (37 mph) and blower is not on high speed.

The instrument panel module (IPM) shall provide the GMLAN Option Information for "Climate Air Quality Sensor Present" and "Climate Control Air Quality Sensitivity Selection" to the HVAC control module. Based on the option information sent to the HVAC control module by the IPM, the HVAC control module will choose 1 of 7 different sensitivity calibration settings stored in the HVAC module. The IPM sends the signal that tells the HVAC control module which sensitivity setting to use. From production the IPM sends a GMLAN message of 0 which tells the HVAC control module to use the default level 4 sensitivity calibration. The air quality sensitivity message sent to the HVAC module can be changed through the IPM with a TECH 2 and has 7 different air quality sensor calibration settings to choose from, 1 being the most sensitive to exhaust fumes and 7 being the least sensitive to exhaust fumes.

The driver information center (DIC) will display the SERVICE A/C SYSTEM message if the HVAC system has detected a short to ground in the air quality sensor circuit. An open circuit or a short to voltage in the air quality sensor circuit will be diagnosed through symptom based diagnostics because both of these conditions will not turn on the SERVICE A/C SYSTEM message or set a trouble code.

Auxiliary HVAC Control Module

The auxiliary HVAC control module is a non-GM LAN device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and air distribution settings. Airflow to the rear system will be turned off when defrost is selected on the front HVAC control module to direct air to clear the windshield. Auxiliary HVAC temperatures can be set cooler or warmer than the front primary HVAC setting. 5 volts and ground are supplied to the rear HVAC control module from the front HVAC control module. The front HVAC control module monitors the position of the rear air temperature actuator and the rear mode actuator. The front HVAC module will move the actuators to the proper position when it receives a request from the rear HVAC control module on which position to place the actuator.