GM Service Manual Online
For 1990-2009 cars only

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. Listen for an audible click or feel for the click when the vacuum control assembly operates. Command both the ON and OFF states. Repeat the commands as necessary.

  2. Test the control circuit of the solenoid that does not click ON and OFF. Verifies that the HVAC control module is providing ground to the solenoid in the vacuum control assembly.

  3. Tests if ground is constantly being applied to the vacuum control assembly.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

DEFINITION: Air does not flow correctly from the air distribution outlets.

1

Did you perform the HVAC Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

  1. Start the engine
  2. Place the blower motor switch in the OFF position.

Is the blower motor OFF?

--

Go to Step 3

Go to Blower Motor Always On

3

Place the blower motor switch in each speed position.

Does the blower motor operate in any of the speed positions?

--

Go to Step 4

Go to Blower Motor Inoperative

4

Does the blower motor operate in the desired speed[s]?

--

Go to Step 5

Go to Blower Motor Malfunction

5

  1. Install a scan tool.
  2. With a scan tool, observe the Mode Down Button parameter in the Heating and Air Conditioning data list.
  3. Activate the mode down switch.
  4. With a scan tool, observe the Mode Up Button parameter in the Heating and Air Conditioning data list.
  5. Activate the mode up switch.
  6. With a scan tool, observe the Front Defrost Button parameter in the Heating and Air Conditioning data list.
  7. Activate the front defrost switch.

Does the scan tool indicate that each observed parameter changes state when the corresponding switch is activated?

--

Go to Step 6

Go to Step 15

6

  1. Place the blower motor switch in the maximum speed position.
  2. Place the mode switch in the vent position.
  3. Place the recirculation switch in the ON position.
  4. Place the recirculation switch in the OFF position.

Does the recirculation door move from the recirculation position to the outside air position?

--

Go to Step 7

Go to Air Recirculation Malfunction

7

  1. Place the mode switch in each mode position.
  2. Place the defrost switch in the defrost position.

Does the air flow from the correct air distribution outlets in each mode position?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 8

8

  1. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, command each vacuum solenoid ON and OFF.

Does each vacuum solenoid turn ON and OFF with each command?

--

Go to Vacuum Control System Diagnostic

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Disconnect the vacuum control assembly.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit of the vacuum control assembly with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 16

10

  1. Measure the voltage between the ignition 3 voltage circuit of the vacuum control assembly and the applicable control circuit of the vacuum control assembly.
  2. With a scan tool, command the applicable solenoid ON and OFF .

Does the voltage measure near the specified values for each commanded state?

12 V ON

0 V OFF

Go to Step 14

Go to Step 11

11

Does the voltage remain near the specified value with each command?

12 V

Go to Step 13

Go to Step 12

12

Test the appropriate control circuit of the vacuum control assembly for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 15

13

Test the appropriate control circuit of the vacuum control assembly for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 14

14

Inspect for poor connections at the vacuum control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

15

Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

16

Repair the ignition 3 voltage circuit of the vacuum control assembly. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

17

Replace the vacuum control assembly. Refer to Vacuum Control Assembly Replacement .

Did you complete the replacement?

--

Go to Step 19

--

18

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

--

Go to Step 19

--

19

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2