HVAC Systems - Automatic: Diagnosis Chevrolet Silverado 1500 HD

Scan Tool Data Definitions

A/C Pressure Sensor: The scan tool displays 0-3450 kPa (0-500 psi). The voltage applied to the PCM input from the A/C refrigerant pressure sensor is converted to a pressure value.

A/C Pressure Sensor: The scan tool displays 0-5 volts. The voltage applied to the PCM input for the A/C refrigerant pressure sensor.

A/C Switch: The scan tool displays On/Off. The scan tool displays On when the A/C request switch is active. The scan tool displays Off when the A/C request switch is inactive.

AC Permission: The scan tool displays Withheld/Granted. The scan tool displays Granted when the HVAC control module determines that conditions for compressor clutch engagement are present. The scan tool displays Withheld when the HVAC control module determines that conditions for compressor clutch engagement are not present.

A/C Relay Command: The scan tool displays On/Off. The scan tool displays the control decision for the compressor clutch relay output as determined by the PCM.

A/C Request Signal: The scan tool displays Yes/No. The scan tool displays Yes when the PCM receives a class 2 message from the HVAC control module to engage the A/C compressor clutch. The scan tool displays No when the PCM receives a class 2 message from the HVAC control module to disengage the A/C compressor clutch.

Air Inlet Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired recirculation door position as determined by the HVAC control module.

Air Inlet Door Actual: The scan tool displays 0-255 counts. The voltage applied to the recirculation door position input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Air Inlet Drive Motor: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Air Mix Door Left Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired left air temperature door position as determined by the HVAC control module.

Air Mix Door Right Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired right air temperature door position as determined by the HVAC control module.

Auto Switch: The scan tool displays On/Off. The scan tool displays On when the automatic switch is active. The scan tool displays Off when the automatic switch is inactive.

Battery Voltage: The scan tool displays 0-25 volts. The voltage measured from the battery positive voltage circuit and the ground circuit of the HVAC control module.

Blower Motor PWM: The scan tool displays 0-114%. The scan tool displays the control decision for the blower motor speed as determined by the HVAC control module. The scan tool displays 114% when the blower motor is commanded to maximum speed. The scan tool displays 0% when the blower motor is commanded OFF.

Engine Coolant Temp: The scan tool displays -39 to 140°C (-38 to 284°F). The scan tool displays the engine coolant temperature as detected by the PCM.

ECT Sensor: The scan tool display -39 to 140°C (-38 to 284°F). The voltage applied to the PCM input from the engine coolant temperature sensor is converted to a temperature value.

ECT Sensor: The scan tool displays 0-5 volts. The voltage applied to the PCM input for the engine coolant temperature sensor.

Fan Down Button: The scan tool displays On/Off. The scan tool displays On when the fan down switch is active. The scan tool displays Off when the fan down switch is inactive.

Fan Up Button: The scan tool displays On/Off. The scan tool displays On when the fan up switch is active. The scan tool displays Off when the fan up switch is inactive.

Front Defrost Switch: The scan tool displays On/Off. The scan tool displays On when the defrost switch is active. The scan tool displays Off when the defrost switch is inactive.

Ign. Since Current DTC: The scan tool displays 0-100. The number of the ignition cycles since the setting of the most recent current diagnostic trouble code (DTC).

Inside Air Temp Fan: The scan tool displays On/Off. The scan tool displays the control decision for the fan motor output as determined by the HVAC control module. The fan motor is internal to the inside air temperature sensor assembly.

Inside Air Temp: The scan tool displays -40 to 215°C (-40 to 419°F). The voltage applied to the HVAC control module input for the inside air temperature sensor is converted to a temperature value.

Left Mix Door Actual: The scan tool displays 0-255 counts. The voltage applied to the left air temperature door position input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Left Mix Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Left Solar Sensor: The scan tool displays 0-255 counts. The voltage applied to the left sunload input of the BCM is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Left Temp. Setting: The scan tool displays 15 to 32°C (60 to 90°F). The scan tool displays the selected temperature from the left air temperature switch.

LH AC Duct Actual: The scan tool displays 0-255 counts. The voltage applied to the left upper duct air temperature input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

LH AC Duct Desired: The scan tool displays 0-255 counts. The desired value of the left upper duct air temperature input. The HVAC control module monitors the actual value of the duct air temperature input and accordingly positions the left air temperature door to achieve the desired duct air temperature.

LH Heater Duct Actual: The scan tool displays 0-255 counts. The voltage applied to the left lower duct air temperature input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

LH Heater Duct Desired: The scan tool displays 0-255 counts. The desired value of the left lower duct air temperature input. The HVAC control module monitors the actual value of the duct air temperature input and accordingly positions the left air temperature door to achieve the desired duct air temperature.

Mode Door Actual: The scan tool displays 0-255 Counts. The voltage applied to the HVAC control module input for the mode door position is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Mode Commanded: The scan tool displays 0-255 counts. The scan tool displays the desired mode door position as determined by the HVAC control module.

Mode Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Mode Select Position: The scan tool displays Off, Auto, Defrost, Heater, Htr/Def, Bi-Level, Panel. The scan tool displays the state of mode operation.

Mode Switch: The scan tool displays On/Off. The scan tool displays On when the mode switch is active. The scan tool displays Off when the mode switch is inactive.

Off Switch: The scan tool displays On/Off. The scan tool displays On when the Off switch is active. The scan tool displays Off when the Off switch is inactive.

Outside Air Temp. Filtered: The scan tool displays -40 to 215°C (-40 to 419°F). The current value of the ambient air temperature display on the HVAC control module.

Outside Air Temp. Raw: The scan tool displays -40 to 215°C (-40 to 419°F). The voltage applied to the HVAC control module input from the ambient air temperature sensor is converted to an unfiltered temperature value.

Pressure Cycle Switch: The scan tool displays Low Pressure/Normal. The current state of the input from the A/C low pressure switch. The scan tool displays Low Pressure when the switch is open and displays Normal when the switch is closed. The low pressure switch opens when low side pressure decreases to approximately 151 kPa (22 psi) and closes when the low side pressure increases to approximately 275 kPa (40 psi).

Recirculate Switch: The scan tool displays On/Off. The scan tool displays On when the recirculation switch is active. The scan tool displays Off when the recirculation switch is inactive.

RH AC Duct Actual: The scan tool displays 0-255 counts. The voltage applied to the right upper duct air temperature input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

RH AC Duct Desired: The scan tool displays 0-255 counts. The desired value of the right upper duct air temperature input. The HVAC control module monitors the actual value of the duct air temperature input and accordingly positions the right air temperature door to achieve the desired duct air temperature.

RH Heater Duct Actual: The scan tool displays 0-255 counts. The voltage applied to the right lower duct air temperature input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

RH Heater Duct Desired: The scan tool displays 0-255 counts. The desired value of the right lower duct air temperature input. The HVAC control module monitors the actual value of the duct air temperature input and accordingly positions the right air temperature door to achieve the desired duct air temperature.

Right Mix Door Actual: The scan tool displays 0-255 counts. The voltage applied to the right air temperature door position input of the HVAC control module is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Right Motor Drive: The scan tool displays Stop, Increase, or Decrease. The scan tool displays the control decision for the actuator output as determined by the HVAC control module.

Right Solar Sensor: The scan tool displays 0-255 counts. The voltage applied to the BCM input from the right sunload sensor is converted to a number between 0 and 255 where 51 Counts is approximately equal to 1 V.

Right Temp. Setting: The scan tool displays 15 to 32°C (60 to 90°F). The scan tool displays the selected temperature from the right air temperature switch.

Diagnostic Trouble Code (DTC) List

Scheme 84

Circuit Description

The following DTCs are for the ambient air temperature sensor and for the inside air temperature sensor assembly

1. B0159 is for the ambient air temperature sensor.
2. B0164 is for the inside air temperature sensor assembly.

The ambient air temperature sensor allows the HVAC control module to monitor the temperature of the air surrounding the front of the vehicle. The inside air temperature sensor assembly allows the HVAC control module to monitor the temperature of the air inside the passenger compartment. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuits. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. The HVAC control module also uses the ambient air temperature input to calculate the value of the ambient air temperature display. When the air temperatures are cold, the resistances 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.

Conditions for Running the DTC

1. Battery voltage to the HVAC control module is greater than 8.7 V and less than 16.5 V.
2. The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control module determines that the voltage applied to the input for the air temperature sensor is less than 0.09 V or greater than 4.9 V.

Action Taken When the DTC Sets

1. The HVAC control module uses a default value of 10°C (50°F) for the ambient air temperature display. The scan tool also displays 10°C (50°F) as the value for the Outside Air Temp. Raw parameter.
2. The HVAC control module use a default value of 25°C (77°F) for the Inside Air Temp. parameter.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the air temperature sensors located in the discharge air ducts

1. B0174 is for the upper left air temperature sensor.
2. B0179 is for the lower left air temperature sensor.
3. B0510 is for the upper right air temperature sensor.
4. B0515 is for the lower right air temperature sensor.

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 V is approximately equal to 51 counts.

1. Battery voltage is within 8.7-16.5 V.
2. The ignition is ON.

The HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.

The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

1. The DTC will become history if the HVAC control module no longer detects a fault.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the left and right sunload sensors.

1. B0183 is for the left sunload sensor.
2. B0188 is for the right sunload sensor.

The left and right sunload sensors provide the HVAC control module with inputs as to the amount heat load the sun is placing on the interior of the vehicle. The sunload sensors are photodiodes that are sensitive to light intensity. The Body Control Module (BCM) applies 5 volts to internal input resistors that are connected to the left and right signal circuits of the sunload sensor assembly. The BCM provides ground to the sensors through the low reference circuit. The BCM monitors the voltage drops across the sunload sensors and converts the voltage values to count values where 1 V is approximately equal to 51 counts. As the light intensity increases, the sunload sensors allow more current to travel through the circuits and the signal voltages decrease. As the light intensity decreases, the sunload sensors allow less current to travel through the circuits and the signal voltages increase. The BCM transmits the data to the HVAC control module over the class 2 serial data circuit.

The ignition is ON.

The BCM determines that the value of the sunload sensor signal is less than 5 counts or greater than 250 counts.

The action taken will be for the BCM to revert to a calibrated default value.

1. The DTC will become history if the BCM no longer detects a failure.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The following DTCs are for the HVAC door actuators

1. B0229 is for the recirculation actuator.
2. B0414 is for the left air temperature actuator.
3. B0424 is for the right air temperature actuator.
4. B3770 is for the mode actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5 volt source voltage to the potentiometer on the 5 volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The module converts the voltage value to a count value where 1 volt is approximately equal to 51 counts.

The HVAC control module calibrates the travel range of the HVAC door actuators when it is initially powered by the battery positive voltage circuit. During calibration, the module commands the actuators in each direction until door travel is stopped. The module stores the minimum door positions and the maximum door positions of each actuator into memory. The total travel range is calculated by subtracting the minimum door position from the maximum door position. The door actuators can be calibrated again with a scan tool.

1. Battery voltage is 8.7-16.5 volts.
2. The ignition is ON.

The DTC sets when one of the following conditions are present

1. The actual door position value for the actuator is less than 5 counts.
2. The actual door position value for the actuator is greater than 250 counts.
3. The actuator fails calibration because the calculated travel range value is too great or too small.

1. If the DTC sets because the actual door position value is out of range, the HVAC control module will command the actuator to a default position.
2. If the DTC sets because the actuator failed a calibration, the HVAC control module will attempt to calibrate the motor in the next transition from OFF to RUN mode.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

1. If the condition is not present refer to «TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS»(ref-170169)
2. If the DTC sets following a calibration of the door actuator, inspect the door and the actuator for the following conditions: A misaligned actuator Broken linkages or binding linkages A broken door or a binding door An obstruction that prevents the door from operating within the full range of motion Missing seals to the door Poor connections at the harness connector of the door actuator

The following DTCs are for the HVAC door actuators

1. B0263 is for the mode actuator.
2. B0268 is for the recirculation actuator.
3. B0408 is for the left air temperature actuator.
4. B0418 is for the right air temperature actuator.

The HVAC control module control the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5-volt signal increases the door position. A 0-volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5-volt signal to the door actuator and motor rotation stops. The ignition 3-voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit.

1. Source voltage is 8.7-16.5 volts.
2. The ignition is ON.
3. The HVAC control module commands the actuator to move.

The actual door position is not near the commanded door position.

The HVAC control module does not command the actuator to move for the remainder of the ignition cycle.

1. The DTC becomes history during the next ignition cycle in which the HVAC control module no longer detects a stall condition.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

1. If the condition is not present, refer to «TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS»(ref-170169) .
2. Inspect the appropriate door and door actuator for the following conditions: A misaligned door actuator Binding linkages A binding door An obstruction that prevents the door actuator from operating within the full range of motion

The ignition 3 voltage circuit is a discrete input to the HVAC control module. The HVAC control modules uses the input to determine that the ignition switch is in the RUN position. When the ignition switch is in the RUN position, ignition voltage is applied to the input.

1. Source voltage is 8.7-16.5 volts.
2. The HVAC control module receives a RUN power mode message from the BCM over the class 2 serial data circuit.

The HVAC control module does not detect ignition voltage on the ignition 3 voltage input.

The HVAC control module will continue to operate using the class 2 power mode messaging.

Scheme 85

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

The powertrain control module (PCM) or engine control module (ECM) 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 too high the PCM will not allow the A/C compressor clutch to engage.

The PCM/ECM detects an A/C request.

1. The A/C refrigerant pressure sensor signal is less than 0.1 volts for 5 seconds.
2. The A/C refrigerant pressure sensor signal is greater than 4.9 volts for 5 seconds.

The malfunction indicator lamp (MIL) will not illuminate.

1. The DTC will become history if the PCM/ECM 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.

For an intermittent, refer to TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System.
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 auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(ref-188963-S36666053962005091100000) .
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-188963-S34504505392005091100000)
2. «HVAC Compressor Clutch Does Not Disengage»(ref-188963-S26881544572005091100000)
3. «Blower Motor Always On»(ref-188963-S24988613152005100600000)
4. «Blower Motor Inoperative»(ref-188963-S25897056852005100600000)
5. «Blower Motor Malfunction»(ref-188963-S05404543582005091100000)
6. «Too Hot in Vehicle»(ref-188963-S02342635942005091100000)
7. «Too Cold in Vehicle»(ref-188963-S38223016082005091100000)
8. «Air Delivery Improper»(ref-188963-S04412888572005091100000)
9. «Air Recirculation Malfunction»(ref-188963-S24748141642005100600000)
10. «LEAK TESTING»(ref-188960-S17164314622005091100000) .
11. «NOISE DIAGNOSIS - BLOWER MOTOR»(ref-188960-S00344029302005100400000) .
12. «NOISE DIAGNOSIS - AIR CONDITIONING (A/C) SYSTEM»(ref-188960-S41139660322005100400000) .
13. «ODOR DIAGNOSIS»(ref-188960-S18414652582005100400000) .

A/C compressor clutch will not engage under the following conditions

1. The A/C high side line pressure is over 2957 kPa (429 psi).
2. The A/C low side line pressure is under 151 kPa (22 psi).
3. Throttle angle is at 100 percent.
4. Engine speed is more than 5500 RPM.
5. Engine coolant temperature (ECT) is more than 121°C (250°F).
6. Ambient air temperature is less than 5°C (40°F).

1. The condition may be intermittent. Refer to «TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS»(ref-170169) .
2. The air temperature actuators can be calibrated. Refer to «Re-Calibrating Actuators»(ref-188963-S03678570172005091100000) .

1. The condition may be intermittent. Refer to «TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS»(ref-170169) .
2. The air temperature actuators can be calibrated. Refer to «Re-Calibrating Actuators»(ref-188963-S03678570172005091100000) .

Preferred Method (w/Scan Tool)

1. Clear all DTCs
2. Place the ignition switch in the OFF position.
3. Install the motor assembly.
4. Re-connect all previously disconnected components.
5. Start the vehicle.
6. With the scan tool, initiate the Motor Re-calibration feature of the HVAC module Special Functions menu.
7. Verify that no DTCs have set as current DTCs.

Alternate Method (w/o Scan Tool)

1. Clear all DTCs
2. Place the ignition switch in the OFF position.
3. Disconnect the scan tool.
4. Install the motor assembly.
5. Re-connect all previously disconnected components.
6. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
7. Re-install the HVAC/ECAS fuse.
8. Start the vehicle.
9. Wait 40 seconds for the HVAC control module to re-calibrate.
10. Verify that no DTCs have set as current DTCs.

Scheme 86

1. Remove the instrument panel accessory trim plate. Refer to «BEZEL REPLACEMENT -- INSTRUMENT PANEL (I/P) CLUSTER»(ref-189012-S39787970842005091100000) .
2. Remove the screws from the HVAC control module.
3. Depress the control assembly retaining tabs and remove the HVAC control module from the instrument panel.
4. Disconnect the electrical connectors from the HVAC control module.