GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Did you perform the HVAC Blower Controls System Check

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Go to Step 2

Go to HVAC Blower Controls System Check

2

  1. Place the ignition switch in the RUN position.
  2. Place the rear heater switch in the HIGH position.
  3. Use a test lamp in order to backprobe from the heater and air conditioning (A/C) control valve solenoid CKT 1596 (GRY/BLK) terminal A to ground.

Did the test lamp light?

--

Go to Step 3

Go to Step 4

3

Connect a test lamp between CKT 1596 (GRY/BLK) terminal A and CKT 850 (BLK) terminal B at the heater and A/C control valve solenoid.

Did the test lamp light?

--

Go to Step 5

Go to Step 6

4

Use a test lamp in order to backprobe from the rear heater switch CKT 1596 (GRY/BLK) terminal C to ground while moving the rear heater switch between LOW, MEDIUM, and HIGH.

Did the test lamp light in all of the settings?

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Go to Step 7

Go to Step 8

5

  1. Ensure that the vacuum supply to the solenoid is not restricted or damaged.
  2. Inspect the vacuum hose between the solenoid and the actual valve for restrictions or cracks.

Does any restrictions or damage exist?

--

Go to Step 9

Go to Step 10

6

Repair the open in CKT 850 (BLK) between the heater and A/C control valve solenoid and splice S108.

Is the repair complete?

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Go to HVAC Blower Controls System Check

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7

Repair the open in CKT 1596 (GRY/BLK) between the rear heater switch and the heater and A/C control valve solenoid.

Is the repair complete?

--

Go to HVAC Blower Controls System Check

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8

Inspect for a poor connection at the rear heater switch.

Did you find a poor connection?

--

Go to Step 14

Go to Step 11

9

Repair or replace the vacuum supply hose as necessary.

Is the repair complete?

--

Go to HVAC Blower Controls System Check

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10

  1. Ensure that the vehicle is reaching the normal operating temperature.
  2. Ensure that the coolant lines are not restricted to the rear heater core.

Do any problems exist?

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Go to Step 12

Go to Step 13

11

Replace the rear heater switch.

Refer to Control Switch Replacement - Auxiliary in Heating and Ventilation (Non-A/C).

Is the replacement complete?

--

Go to HVAC Blower Controls System Check

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12

Repair the damage as necessary.

Is the repair complete?

--

Go to HVAC Blower Controls System Check

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13

Replace the heater and A/C control valve solenoid.

Is the replacement complete?

--

Go to HVAC Blower Controls System Check

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14

Repair the poor connection.

Is the repair complete?

--

Go to HVAC Blower Controls System Check

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