GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Too Hot in Vehicle

Test Description

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

  1. The HVAC control module is inoperative when the module does not respond to an operator control request.

    2.

  2. If the condition does not occur when an A/C request has been made then you must bypass the A/C performance test procedures.

    3.

  3. 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.

  4. Performing the Air Conditioning System Performance Test ensures that the A/C system is operating properly for further testing.

    5.

  5. If no condition found with all conditions listed then compare door travel to known good vehicle.

    6.

  6. 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.

Step

Action

Values

Yes

No

Schematic Reference : HVAC Schematics

DEFINITION: The temperature cannot be adjusted, or the cooling is insufficient during A/C operation.

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2
  1. Turn ON the ignition, with the engine OFF.
  2. Place the blower motor switch in each speed position.

Does the blower motor operate at all?

--

Go to Step 3

Go to Blower Motor Inoperative

3

Does the blower motor operate correctly for each speed position?

--

Go to Step 4

Go to Blower Motor Malfunction

4

Is the HVAC control assembly inoperative?

--

Go to Step 18

Go to Step 5

5

Does the Too Hot in Vehicle concern occur when A/C cooling is desired?

--

Go to Step 6

Go to Step 8

6

Important: For A/C compressor operation, the ambient air temperature must be above 3°C (38°F).

  1. Start the engine.
  2. Place the blower motor switch in the maximum speed position.
  3. Place the A/C request switch in the ON position.
  4. Place the air temperature switch in the coldest position.

Does the A/C compressor operate?

--

Go to Step 7

Go to HVAC Compressor Clutch Does Not Engage

7

Perform the refrigerant system performance test. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation, and Air Conditioning.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 8

8
  1. Observe the drive shaft of the air temperature actuator.
  2. Adjust the air temperature switch.

Does the drive shaft of the air temperature actuator ever rotate?

--

Go to Step 9

Go to Step 10

9

Inspect the air temperature door and the air temperature actuator for the following conditions:

    • A misaligned air temperature actuator.
        Refer to Air Temperature Actuator Replacement
    • Broken linkages or binding linkages
    • A broken air temperature door or a binding air temperature door
    • An obstruction that prevents the air temperature door from operating within the full range of motion
    • Missing seals to the air temperature door
    • Misaligned seals to the air temperature door

Did you find and correct the condition?

--

Go to Step 25

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

10

Test the ignition 3 voltage circuit of the air temperature actuator for an open or for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 11

11

Test the ground circuit of the air temperature actuator for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 12

12

Test the 5-volt reference circuit of the air temperature actuator for a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 13

13

Test the signal circuit of the air temperature door actuator an open or a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 14

14

Test the door control circuit of the air temperature actuator an open or a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 15

15

Important: Ensure the air temperature actuator connector and the HVAC control assembly connectors are connected during this step to avoid misdiagnosis.

  1. Turn ON the ignition, with the engine OFF.
  2. Backprobe and monitor the voltage from the door signal circuit of the air temperature actuator to a good ground.
  3. Connect a 3-ampere fused jumper between the door control circuit and the 5-volt reference circuit of the air temperature actuator. This action drives the actuator to the full COOL mode.
  4. Remove and reconnect the jumper wire between the air temperature door control and the ground circuit of the air temperature actuator. This action drives the actuator to the full HOT mode.

Does the drive shaft of the air temperature actuator rotate and does the voltage change?

--

Go to Step 16

Go to Step 20

16

Important:: Ensure the air temperature actuator connector is connected during this step to avoid misdiagnosis.

  1. Backprobe the connector terminal of the air temperature actuator in order to measure the voltage from the door control circuit to ground.
  2. Adjust the air temperature switch.

Is the voltage measurement near the specified value in each condition?

0 V increasing

5 V decreasing

2.5 V stationary

Go to Step 17

Go to Step 22

17

Inspect the air temperature door for a mechanical condition or for a condition that allows excessive travel of the door.

Did you find and correct the condition?

--

Go to Step 25

--

18

Test the ignition-3 voltage circuit of the HVAC control assembly for an open, for a high resistance, or for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 19

19

Test the ground circuit of the HVAC control assembly for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 22

20

Inspect for poor connections at the harness connector of the air temperature actuator. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 21

21

Inspect the air temperature actuator, the door, and any attaching linkage for binding or for a condition that prevents drive shaft rotation.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 23

22

Inspect for poor connections at the harness connector of the HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 25

Go to Step 24

23

Important: Perform the calibration procedure for the air temperature actuator.

Replace the air temperature actuator. Refer to Air Temperature Actuator Replacement .

Did you complete the replacement?

--

Go to Step 25

--

24

Important: Perform the calibration procedure for the HVAC control assembly.

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

--

Go to Step 25

--

25

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2