GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Was the heater-A/C Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2

Inspect the HVAC fuse in the fuse block.

Is the HVAC fuse open?

--

Go to Step 3

Go to Step 4

3

Locate and repair a short to ground in circuit 41 (BRN). Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 14

--

4

  1. Place the ignition switch in the on position.
  2. Connect a test lamp between the vacuum/electric solenoid harness connector terminal 6 and ground.

Does the test lamp light?

--

Go to Step 6

Go to Step 5

5

Locate and repair a poor connection or an open in circuit 41 (BRN). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 14

--

6

  1. Place the heater A/C control in the Bi-Level position.
  2. Turn the A/C to the OFF position.
  3. Connect a test lamp between B+ and the vacuum/electric solenoid harness connector terminal 3 (circuit 361).

Does the test lamp light?

--

Go to Step 9

Go to Step 7

7

Inspect for a poor connection or open in circuit 361 (PPL). Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Is there a poor connection or open in the circuit?

--

Go to Step 8

Go to Step 12

8

Locate and repair the poor connection or open in circuit 361 (PPL). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 14

--

9

  1. Place the mode selector in the UPPER position.
  2. Use a digital multimeter (DMM) in order to test for a short to ground on circuit 706 (LT BLU) at the vacuum/electric solenoid connector terminal 5.

Does the test lamp light?

--

Go to Step 10

Go to Step 13

10

Use a DMM in order to test for a short to ground on circuit 706 (LT BLU) at the heater-A/C control connector C2, terminal A8.

Does the test lamp light?

--

Go to Step 11

Go to Step 12

11

Locate and repair the short to ground in circuit 706 (LT BLU) between the heater-A/C control harness connector and the vacuum/electric solenoid harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 14

--

12

Replace the heater-A/C control. Refer to Control Assembly Replacement .

Is the repair complete?

--

Go to Step 14

--

13

There is a fault in one of the following areas:

    • The vacuum/electric solenoid
    • The vacuum source
    • The vacuum actuators
    • The vacuum hoses to actuators
    • The linkage from actuators to valves
    • Malfunctioning valves

Is the action complete?

--

Go to Step 14

--

14

Verify that the system operates properly.

Does the system operate properly?

--

System OK

Go to Diagnostic System Check