GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Too Cold in Vehicle - Auxiliary

Test Description

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

  1. This checks for proper cooling system operation.

    2.

  2. Checks for proper system vacuum at the heater water valve.

    3.

  3. Checks the control circuit of the heater water valve for a circuit fault.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: Auxiliary 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

Does the HVAC control assembly operate and provide sufficient heating?

Go to Step 3

Go to Too Cold in Vehicle

3
  1. Turn ON the ignition, with the engine OFF.
  2. Place the heater auxiliary blower motor switch in each speed position.

Does the heater auxiliary blower motor operate at all?

Go to Step 4

Go to Auxiliary Blower Motor Inoperative

4

Does the heater auxiliary blower motor operate correctly for each speed position?

Go to Step 5

Go to Auxiliary Blower Motor Malfunction

5

Inspect the cooling system for the following:

    • Low coolant level
    • Loose or worn accessory drive belt
    • Leaking or kinked radiator or auxiliary heater hoses
    • Missing radiator filler cap pressure seal
    • Improper radiator filler cap operation

Did you find and correct the condition?

Go to Step 14

Go to Step 6

6

  1. Disconnect the vacuum hose from the heater water valve.
  2. Start the engine.
  3. Place the auxiliary heater blower motor switch in the LO, MED or HI positions.

Is there engine vacuum present at the heater water valve vacuum hose?

Go to Step  7

Go to Vacuum Control System Diagnostic

7

  1. Turn OFF the ignition.
  2. Disconnect the heater water valve solenoid.
  3. Connect a test lamp between the heater water control solenoid control circuit of the heater water valve solenoid and a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Place the auxiliary heater blower motor switch in the LO, MED or HI positions.

Does the test lamp illuminate?

Go to Step 8

Go to Step 9

8

Test the ground circuit of the heater water valve solenoid for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 10

9

Test the heater water control solenoid control circuit of the heater water valve solenoid for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 11

10

Inspect for poor connections at the harness connector of the heater water valve solenoid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 12

11

Inspect for poor connections at the harness connector of the auxiliary heater blower motor switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 14

Go to Step 13

12

Replace the heater water valve. Refer to Heater Water Valve Replacement .

Did you complete the replacement?

Go to Step 14

--

13

Replace the auxiliary heater blower motor switch. Refer to Heater Control Blower Switch Replacement .

Did you complete the replacement?

Go to Step 14

--

14

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2