GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Corvette 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Air Delivery Improper

Step

Action

Value(s)

Yes

No

DEFINITION: Air flow is not being delivered from the proper mode outlet which was requested by the operator.

1

Where you sent here from the HVAC System Check?

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Go to Step 2

Go to HVAC System Check

2
  1. Remove the I/P RH lower insulator.

    2. Refer to Instrument Panel Insulator Panel Replacement in Instrument Panel, Gauges and Console.

  2. Disconnect the I/P harness vacuum connector from the HVAC module violet vacuum (source) line.
  3. Connect a vacuum gauge to the I/P harness vacuum line.
  4. Start the engine and allow the engine to idle.
  5. Measure the vacuum at the I/P harness (engine source) vacuum line.

Is the vacuum reading within the specified value?

69-117 kPa (10-17 in Hg)

Go to Step 3

Go to Step 4

3
  1. Turn OFF the engine.
  2. Inspect the vacuum reading at the I/P harness (engine source) vacuum line.

Does the vacuum reading hold steady?

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Go to Step 11

Go to Step 6

4
  1. Remove the RH front wheelhouse filler panel.

    2. Refer to Wheelhouse Filler Replacement in Body Front End.

  2. Disconnect the engine harness vacuum connector from the vacuum tank check valve.
  3. Connect a vacuum gauge to the engine harness vacuum (source) line.
  4. Start the engine and allow the engine to idle.
  5. Measure the vacuum at the engine harness vacuum (source) line.

Is the vacuum reading within the specified value?

69-117 kPa (10-17 in Hg)

Go to Step 6

Go to Step 5

5

Repair the leak or restriction in the engine harness vacuum (source) line.

Is the repair complete?

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Go to Step 20

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6
  1. Connect a vacuum gauge to the vehicle interior end of the I/P harness vacuum line.
  2. Remove the RH front wheelhouse filler panel.
  3. Disconnect the I/P harness vacuum connector from the vacuum tank check valve.
  4. Connect a hand vacuum pump to the vehicle exterior end of the I/P harness vacuum line.
  5. Apply 103-108 kPa (15-20 inches) of vacuum to the line.
  6. Measure the vacuum on the vacuum gauge inside the vehicle.

Is the vacuum reading the same as the amount of vacuum applied and does the vacuum reading hold steady?

--

Go to Step 8

Go to Step 7

7

Repair the leak or restriction in the I/P harness vacuum (engine source) line.

Is the repair complete?

--

Go to Step 20

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8
  1. Disconnect the vacuum tank check valve from the vacuum tank.
  2. Connect a hand vacuum pump to the vacuum tank.
  3. Apply 103-108 kPa (15-20 inches) of vacuum to the vacuum tank.

Does the vacuum reading hold steady?

--

Go to Step 9

Go to Step 10

9

Replace the vacuum tank check valve.

Is the repair complete?

--

Go to Step 20

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10

Replace the vacuum tank. Refer to Vacuum Tank Replacement .

Is the repair complete?

--

Go to Step 20

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11
  1. Remove the I/P accessory trim plate.

    2. Refer to Instrument Panel Accessory Trim Plate Replacement in Instrument Panel, Gauges and Console.

  2. Remove the I/P upper trim pad.

    3. Refer to Instrument Panel Upper Trim Pad Replacement in Instrument Panel, Gauges and Console.

  3. Remove the HVAC control head.

    4. Refer to Control Assembly Replacement .

  4. Plug one of the two HVAC control head ends of the violet vacuum line and install a vacuum gauge to the other.
  5. Connect a hand vacuum pump to the underdash end of the violet vacuum line.
  6. Apply 103-108 kPa (15-20 inches) of vacuum to the vacuum line.
  7. Measure the amount of vacuum on the vacuum gauge.
  8. Switch the connection of the vacuum gauge and the plug between the two HVAC control head ends of the violet vacuum line.
  9. Apply 103-108 kPa (15-20 inches) of vacuum to the vacuum line.
  10. Measure the amount of vacuum on the vacuum gauge.

Is the vacuum reading the same as the amount of vacuum applied and does the vacuum reading hold steady?

--

Go to Step 13

Go to Step 12

12

Repair the leak or restriction in the HVAC module violet vacuum (source) line.

Is the repair complete?

--

Go to Step 20

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13
  1. Connect a hand vacuum pump to each of the remaining vacuum lines, one at a time, at the connector which attaches to the HVAC control head.
  2. Apply 103-108 kPa (15-20 inches) of vacuum to each vacuum line.
  3. Observe the operation of the vacuum actuator and the related valve(s) to which the vacuum line is attached.

Does each vacuum line, actuator and related valve(s) hold vacuum and operate properly?

--

Go to Step 19

Go to Step 14

14
  1. Disconnect the vacuum line(s) from the vacuum actuator(s) which did not operate properly.
  2. Connect a hand vacuum pump to the vacuum actuator.
  3. Apply 103-108 kPa (15-20 inches) of vacuum to the vacuum actuator.
  4. Observe the operation of the vacuum actuator and the related valve(s).

Does the vacuum actuator hold vacuum?

--

Go to Step 16

Go to Step 15

15

Replace the faulty vacuum actuator.

    • For mode valve vacuum actuator replacement, refer to Mode Actuator Replacement .
    • For defroster valve vacuum actuator replacement, refer to Defroster Valve Actuator Replacement .
    • For air inlet valve vacuum actuator replacement, refer to Air Inlet Actuator Replacement .

Is the repair complete?

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Go to Step 20

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16

Is a binding condition evident, not allowing proper actuation of the related valve(s)?

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Go to Step 17

Go to Step 18

17

Repair the binding condition.

Is the repair complete?

--

Go to Step 20

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18

Repair the leak or restriction in the affected vacuum line.

Is the repair complete?

--

Go to Step 20

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19

Replace the HVAC control head. Refer to Control Assembly Replacement .

Is the repair complete?

--

Go to Step 20

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20

Install components or connectors which were removed or disconnected.

Is the action complete?

--

Go to HVAC System Check

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