GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Symptoms

2

Inspect the HTR-A/C Fuse 12 at the IP fuse block.

Is the fuse operational?

--

Go to Step 4

Go to Step 3

3

  1. Locate and repair the overload. Refer to Circuit Testing in Wiring Systems.
  2. Replace the HTR-A/C Fuse 12.

Did you complete the repair?

--

Go to Step 27

--

4

Inspect the RR Heat A/C Fuse at the Underhood Fuse Block.

Is the fuse operational?

--

Go to Step 6

Go to Step 5

5

  1. Locate and repair the overload. Refer to Circuit Testing in Wiring Systems.
  2. Replace the RR Heat A/C Fuse.

Did you complete the repair?

--

Go to Step 27

--

6

  1. Disconnect the rear heater blower motor.
  2. Turn ON the ignition, with the engine OFF.
  3. Place the rear heater switch in the HIGH position.
  4. Connect a test lamp between the rear heater blower motor CKT 1172 (YEL) at the blower motor to ground.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 8

7

Connect a test lamp between CKT 1172 (YEL) and CKT 1150 (BLK) at the rear heater blower motor.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 11

8

  1. Disconnect the air conditioning (A/C) enable relay (rear).
  2. Connect a test lamp between CKT 1040 (ORN) cavity A9 at the A/C enable relay (rear) to ground.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 13

9

Inspect for a poor connection at the rear heater blower motor.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find a poor connection?

--

Go to Step 10

Go to Step 14

10

Repair the poor connection.

Refer to Connector Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

11

Repair the open in CKT 1150 (BLK).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

12

Connect a test lamp between CKT 141 (BRN) cavity A7 at the A/C enable relay (rear) to ground.

Does the test lamp illuminate?

--

Go to Step 15

Go to Step 16

13

Repair the open in CKT 1040 (ORN).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

14

Replace the rear heater blower motor.

Refer to Refrigerant Recovery and Recharging in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

--

Go to Step 27

--

15

Connect a test lamp between CKT 141 (BRN) cavity A7 to CKT 850 (BLK) cavity B9 at the A/C enable relay (rear).

Does the test lamp illuminate?

--

Go to Step 17

Go to Step 18

16

Repair the open in CKT 141 (BRN).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

17

  1. Reconnect the A/C enable relay (rear).
  2. Using a test lamp backprobe from the A/C enable relay (rear) CKT 1923 (ORN) cavity B7 to ground.

Does the test lamp illuminate?

--

Go to Step 19

Go to Step 20

18

Repair the open in CKT 850 (BLK).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

19

Using a test lamp backprobe from the rear heater switch CKT 1923 (ORN) cavity G to ground.

Does the test lamp illuminate?

--

Go to Step 21

Go to Step 22

20

Replace the A/C enable relay (rear).

Refer to Blower Motor Relay Replacement in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

--

Go to Step 27

--

21

Using a test lamp backprobe from the rear heater switch CKT 1924 (WHT) cavity A to ground.

Does the test lamp illuminate?

--

Go to Step 23

Go to Step 24

22

Repair the open in CKT 1923 (ORN).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

23

Using a test lamp backprobe from the rear heater resistor pack CKT 1924 (WHT) cavity B to ground.

Does the test lamp illuminate?

--

Go to Step 25

Go to Step 26

24

Replace the rear heater switch.

Refer to Control Switch Replacement - Auxiliary in Heating, Ventilation, and Air Conditioning.

Did you complete the replacement?

--

Go to Step 27

--

25

Repair the open in CKT 1172 (YEL).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

26

Repair the open in CKT 1924 (WHT), CKT 1925 (RED) and CKT 1926 (DK BLU).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

27

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2