GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Too Cold 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 no condition found with all conditions listed then compare door travel to known good vehicle.

    3.

  3. 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 heating is insufficient.

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 operate in any of the speed positions?

--

Go to Step 3

Go to Blower Motor Inoperative

3

Does the blower actuator 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 17

Go to Step 5

5

Inspect the cooling system for the following:

    • A low coolant level
    • A loose or worn accessory drive belt
    • Leaking radiator hoses or leaking heater hoses
    • Kinked radiator hoses or kinked heater hoses
    • A missing radiator cap pressure seal
    • A leaking radiator cap

Did you find and correct the condition?

--

Go to Step 24

Go to Step 6

6
  1. Start the engine.
  2. Place the blower motor switch in the OFF position.
  3. Place the A/C request switch in the OFF position.

Does the A/C compressor operate?

--

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 7

7
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the drive shaft of the air temperature door actuator.
  3. Adjust the air temperature switch.

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

--

Go to Step 8

Go to Step 9

8

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

    • A misaligned actuator on the air temperature door
    • 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 24

Go to Heating Performance Diagnostic

9

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 24

Go to Step 10

10

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 24

Go to Step 11

11

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 24

Go to Step 12

12

Test the signal 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 24

Go to Step 13

13

Test the control 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 24

Go to Step 14

14

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

  1. Turn ON the ignition, with the engine OFF.
  2. Backprobe and monitor the voltage from the signal circuit of the air temperature door actuator to a good ground.
  3. Connect a 3-ampere fused jumper between the control circuit and the 5-volt reference circuit of the air temperature door 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 door actuator rotate and does the voltage change?

--

Go to Step 15

Go to Step 19

15

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

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

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

0 V increasing

5 V decreasing

2.5 V stationary

Go to Step 16

Go to Step 21

16

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

Did you complete the repair?

--

Go to Step 24

--

17

Test the ignition 3 voltage circuit of the HVAC controller 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 24

Go to Step 18

18

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

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

19

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 24

Go to Step 20

20

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 24

Go to Step 22

21

Inspect for poor connections at the harness connector of the HVAC control module. 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 24

Go to Step 23

22

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

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

Did you complete the replacement?

--

Go to Step 24

--

23

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

Did you complete the replacement?

--

Go to Step 24

--

24

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2