HVAC Systems - Automatic: Diagnosis Pontiac Aztek I

Scan Tool Data Definitions

The HVAC Scan Tool Data Definitions contain a brief description of all the scan tool parameters. This list is in alphanumeric order.

A/C High Side Pressure: The scan tool displays -103 to +3119 kPa (-14 to +452 psi). This parameter represents the A/C refrigerant pressure sensor voltage signal converted to pressure.

A/C High Side Pressure: The scan tool displays 0.00-5.00 Volts. This parameter represents the A/C refrigerant pressure sensor signal.

A/C Off For WOT: The scan tool displays Yes or No. Yes indicates that the PCM has disabled the A/C compressor because the TP sensor signal is at wide open throttle.

A/C Pressure Disable: The scan tool displays Yes or No. Yes indicates that the PCM has disabled the A/C compressor due to excessive refrigerant pressure.

A/C Request: The scan tool displays Yes or No. The PCM uses the A/C request signal in order to determine if A/C compressor operation is being requested by the HVAC control module.

A/C Request Signal: The scan tool displays Yes or No. The PCM uses the A/C request signal in order to determine if A/C compressor operation is being requested by the HVAC control module.

A/C Relay Command: The scan tool displays On or Off. Represents the PCM commanded state of the A/C compressor clutch relay. The A/C compressor clutch should be engaged when Commanded A/C displays On.

Ambient Air Temperature: The scan tool displays -50 to +87.5°C (-58 to +189.5°F). The output of the ambient air temperature sensor.

Auto Mode: The scan tool displays On or Off. When in Auto mode the scan tool displays On. When in Manual mode the scan tool displays Off.

Auto Button: The scan tool displays On or Off. When the AUTO button is pressed the scan tool displays On. When released, the scan tool displays Off.

Blower Speed: The scan tool displays 0 to 8 bars. When the blower motor is commanded off the scan tool displays 0. When the blower motor controls are placed in the maximum speed setting the scan tool displays 8 bars. This coincides with the HVAC control module display.

Evaporator Temp: This data displays -40 to 87.5°C (-40 to 189.5°F). The output of the evaporator temperature sensor.

Fan Down Button: The scan tool displays On or Off. When the Blower Speed Control Down button is pressed the scan tool displays On. When released, the scan tool displays Off.

Fan Up Button: The scan tool displays On or Off. When the Blower Speed Control Up button is pressed the scan tool displays On. When released, the scan tool displays Off.

Front Defrost Button: The scan tool displays On or Off. When the Front Defrost button is pressed the scan tool displays On. When released, the scan tool displays Off.

Inside Air Temperature: The scan tool displays -50 to +87.5°C (-58 to +189.5°F). The output of the inside air temperature sensor.

Left Temp Door Position: The scan tool displays 0 to 195 counts. The signal output from the feedback pot on the actuator.

Mode Button: The scan tool displays On or Off. When the Mode button is pressed the scan tool displays On. When released, the scan tool displays Off.

Mode Door Position: The scan tool displays Vent, Mix-Blend, Floor, Bi- Level or Defrost. The current operating mode of the HVAC system.

Off Button: The scan tool displays On or Off. When the Off button is pressed the scan tool displays On. When released, the scan tool displays Off.

Rear Defrost Button: The scan tool displays On or Off. When the Rear Defrost button is pressed the scan tool displays On. When released, the scan tool displays Off.

Recirculate Button: The scan tool displays On or Off. When the Recirculate button is pressed the scan tool displays On. When released, the scan tool displays Off.

Recirculation Mode: The scan tool displays Ambient Air or Recirculate. The current operating state of the recirculation door.

Right Temp Door Position: The scan tool displays 0 to 195 counts. The signal output from the feedback pot on the actuator.

Selected Air Mode: The scan tool displays Warm Up, Defrost or Off. The current operating mode of the HVAC system.

Sun Load Sensor: The scan tool displays 0 to 255 counts. The signal output from the Sun Load Sensor.

Vent Button: The scan tool displays On or Off. When the Vent button is pressed the scan tool displays On. When released, the scan tool displays Off.

Scheme 84

Circuit Description

The HVAC control module monitors the passenger compartment inside air temperature through an inside air temperature sensor. The inside air temperature sensor is a integral part of the HVAC control module. When the air is cold, the sensor resistance and the signal voltage are high. When the air is warm, the sensor resistance and the signal voltage are low.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

1. The HVAC control module detects the signal circuit is less than 0.09 volts.
2. The HVAC control module detects the signal circuit is more than 4.90 volts.

Action Taken When the DTC Sets

1. The DTC is stored in DTC information.
2. The HVAC control module will continue to monitor the reference signal of the inside air temperature sensor.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects a condition.
2. The history DTC clears after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

Scheme 85

The mode actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The HVAC control module controls the mode door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. As the actuator moves, the potentiometer produces the actual door position signal that is sent to the HVAC control module. The HVAC control module continues to command the actuator to move until the desired and actual values are equal. The door directs airflow through the outlets as selected by the vehicles occupants.

The HVAC control module commands the actuator through it's full range. The HVAC control module stores the learned minimum and maximum position values. The travel range value is calculated by subtracting the minimum and maximum position values. Then the HVAC control module compares the travel range, minimum and maximum values to calibrated value ranges. If the travel range value is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful. The HVAC control module continuously compares the actual actuator position to the calibrated minimum and maximum position values.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.

1. Mode actuator position signal is less than 5 counts.
2. Mode actuator position signal is more than 194 counts.
3. The mode actuators total travel range is less than or greater than the calibrated limits.

1. The DTC is stored in DTC information.
2. The HVAC control module will continue to make use of whatever travel range is still available.

1. If the HVAC control no longer detects a failure, then the DTC will become history.
2. The history DTC will clear after 50 ignition cycles without a failure.
3. The DTC can be cleared with a scan tool.

1. A damaged or broken mode door and or actuator can cause this DTC to set.
2. If the Mode actuator travels beyond it's calibrated limits the DTC will set.

Scheme 86

Scheme 87

The HVAC control module commands the air temperature actuator movement with one of three voltage signals applied to the air temperature door control circuit. A low voltage of 0 volts moves the air temperature door toward full hot. A voltage of 2.5 volts stops the actuator. A high voltage of 5 volts moves the air temperature door toward full cold. The HVAC control module determines the current position of the actuator by monitoring the feedback voltage of the air temperature door position signal circuit. The feedback potentiometer position is a function of the actuator position. A high voltage indicates a full cold air temperature door position. A low voltage indicates a full hot air temperature door position. The HVAC control module controls the air temperature door position in order to maintain the selected air temperature.

1. The ignition is turned ON.
2. Ignition voltage is between 9-16 volts.

1. The air temperature position signal is less than 5 counts.
2. The air temperature position signal is greater than 194 counts.
3. The air temperature actuator actual total travel range max-min is less than or greater than the range limits.

1. The HVAC control module will continue to make use of whatever air temperature actuator travel range is still available.
2. The DTC is stored in DTC information.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. A damaged or broken air temperature actuator or mode door can cause this DTC to set.
2. If the condition is not present refer to «TESTING FOR INTERMITTENT AND POOR CONNECTIONS»(ref-180867-S22861889912005073000000) .

Scheme 88

Scheme 89

The HVAC control module monitors the temperature of the refrigerant through the evaporator via a evaporator temperature sensor. When the refrigerant temperature is low the sensor resistance and the signal voltage are high. When the refrigerant temperature is high the sensor resistance and the signal voltage are low.

The sensor works in conjunction with a switch to meter the flow of refrigerant therefore preventing the freezing of moisture that condenses on the evaporator. An evaporator with too little refrigerant will starve causing insufficient cooling. An evaporator flooded with refrigerant will also cause poor cooling when there is too much liquid refrigerant that cannot vaporize quickly.

The ignition is turned ON.

The HVAC control module detects the signal circuit is less than 5 counts (0.09 V).

1. The HVAC control module will store the trouble code in memory.
2. A default value will be used for the sensor data by the HVAC control module to allow the A/C system to operate.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The powertrain control module (PCM) monitors the high side refrigerant pressure via a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is high the PCM commands the cooling fans on. When pressure is too high or too low the PCM will not allow the A/C compressor clutch to engage.

1. The engine is running.
2. A/C has been requested.

1. The PCM detects the signal circuit is less than 5 counts (0.09 volt) or more than 250 counts (4.90 volts).
2. The condition exists for 20 seconds.

1. The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
2. The PCM stores the failure records.
3. The A/C compressor clutch is disabled.

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

If the condition is not present refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

The ignition voltage is between 9.0-18.0 volts.

1. A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit to the A/C clutch relay.
2. The condition is present for at least 30 seconds.

1. The PCM will not illuminate the malfunction indicator lamp (MIL).
2. The PCM will store those conditions which were present when the DTC set. These conditions are recorded as Failure Records data only. This information will not be stored as Freeze Frame data.

1. A history DTC will clear after 50 consecutive fault free ignitions have occurred without a malfunction.
2. The DTC can be cleared by using a scan tool.

Important: Inspect PCM engine grounds for being secure and clean.

If DTC P1546 cannot be duplicated, review the Failure Records. Observe the vehicle mileage since the diagnostic test last failed. This may help to determine how often the condition which caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-180867-S01327382262005073000000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating steering wheel or passenger HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «AIR TEMPERATURE DESCRIPTION AND OPERATION»(ref-180864-S20457233682005073000000) .
6. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
7. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

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»(ref-180864-S31005226752005073000000)
2. «HVAC COMPRESSOR CLUTCH DOES NOT DISENGAGE»(ref-180864-S37836668642005073000000)
3. Blower Motor Always on see scheme 43
4. Blower Motor Inoperative see scheme 44
5. «BLOWER MOTOR MALFUNCTION»(ref-180864-S38545868422005073000000)
6. «TOO HOT IN VEHICLE»(ref-180864-S32521646112005073000000)
7. «TOO COLD IN VEHICLE»(ref-180864-S17661550172005073000000)
8. «AIR DELIVERY IMPROPER»(ref-180864-S17765598202005073000000)
9. «AIR RECIRCULATION MALFUNCTION»(ref-180864-S22266887412005073000000)
10. «LEAK TESTING»(ref-180860-S41656829292005073000000)
11. «DEFROSTING INSUFFICIENT»(ref-180860-S25627667612005073000000)
12. «NOISE DIAGNOSIS - BLOWER MOTOR»(ref-180860-S22780593242005073000000)
13. «NOISE DIAGNOSIS - AIR CONDITIONING (A/C) SYSTEM»(ref-180860-S13857524212005073000000)
14. «ODOR DIAGNOSIS»(ref-180860-S15122397722005073000000)
15. «NOISE DIAGNOSIS - HVAC MODULE»(ref-180860-S20095700902005073000000)
16. «OUTSIDE AIR TEMPERATURE DISPLAY INACCURATE OR INOPERATIVE»(ref-180879-S10727148262005073000000)

The Mitsubishi scroll type A/C compressor carries an internal thermal cut off switch. The thermal cut off switch normal operation is to open and disable the compressor under extreme load and temperatures above 155°C (311°F). The internal thermal cut off switch is non-serviceable.

The Mitsubishi scroll type A/C compressor carries an internal thermal cut off switch. The thermal cut off switch normal operation is to open and disable the compressor under extreme load and temperatures above 155°C (311°F). The internal thermal cut off switch is non-serviceable.