If the airflow through the vents changes modes when the vehicle is in operation, or if the airflow remains in any mode and does not change, diagnose the system using the table below.
Start the engine and let the engine idle down. Move the selector knob to each position. (Refer to the vacuum diagrams and the operational charts for the airflow, the door functioning and the vacuum circuits.) Refer to Function Test . If the airflow does not come out of the proper outlet at each selector knob position, complete the following procedure:
- Inspect the hose connections at the following locations:
- Inspect the vacuum source circuit by completing the following steps:
- Inspect the specific vacuum circuits by completing the following steps:
- Inspect the vacuum harness circuit by completing the following steps:
| • | The vacuum actuators |
| • | The control head valve |
| • | The vacuum tank |
| 2.1. | Install a vacuum tee and a gage at the vacuum tank outlet. |
| 2.2. | Idle the engine. |
| 2.3. | Move the selector knob to all of the positions. |
Read the vacuum.
Normal vacuum is equivalent to the manifold vacuum.
| 2.4. | If the vacuum is less than normal in all of the positions, complete the following steps: |
| 2.4.1. | Remove the tee. |
| 2.4.2. | Connect the vacuum gage line to the tank. |
| 2.4.3. | Read the gage. |
Low vacuum indicates a problem in the circuit feed to the tank.
A normal vacuum reading indicates a condition downstream.
| 2.5. | Less than normal vacuum in some positions indicates a leak in the circuits of the affected selector knob position. |
| 2.6. | Normal vacuum in all of the positions indicates a condition caused by improperly connected or plugged lines, or an inoperative vacuum valve. |
| 3.1. | Place the selector knob in the affected position. |
| 3.2. | Inspect for vacuum at the affected vacuum actuator. |
| 3.3. | If vacuum exists at the actuator, but the door does not move, the actuator is inoperative, or is mechanically bound. |
| 3.4. | If the low or no vacuum exists at the actuator, complete the following steps: |
| 3.4.1. | Inspect the vacuum harness. |
| 3.4.2. | Inspect the vacuum valve. |
| 4.1. | Disconnect the vacuum harness at the control head. |
| 4.2. | The green line indicates engine vacuum. |
If engine vacuum does not exists, trace back through the connector to the vacuum tank.
| 4.3. | In order to inspect any individual circuit, complete the following steps: |
| 4.3.1. | Place the selector knob at the affected circuit position. |
| 4.3.2. | Inspect for vacuum. |
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
DEFINITION: The vacuum system is stuck in defrost or changes modes while the vehicle is in operation. Refer to vacuum schematic in HVAC air delivery. | ||||||||||
1 |
Does the vacuum stay the same? | -- | Go to Step 2 | Go to Step 3 | ||||||
2 | Does the vacuum not exist? | -- | Go to Step 5 | Go to Step 3 | ||||||
3 | Replace the hot water vacuum switch. Does the vacuum system operate properly? | -- | Go to Function Test | Go to Step 4 | ||||||
4 |
The vacuum should stay steady. The system should hold a vacuum in each mode for at least 20 seconds. Does the system not hold a vacuum in any mode? | -- | Go to Step 5 | Go to Step 6 | ||||||
5 | Inspect the source vacuum in the following components:
Did you find and repair a condition? | -- | Go to Function Test | Go to Step 6 | ||||||
6 |
Is a leak audible? | -- | Go to Step 7 | Go to Step 8 | ||||||
7 | Replace the control assembly. Does the vacuum system operate properly? | -- | Go to Function Test | Go to Step 8 | ||||||
8 | Apply the specified amount of vacuum to each port at the rotary vacuum switch harness. Does the system hold vacuum? | 103.4 kPa (15 psi) | Go to Function Test | Go to Step 9 | ||||||
9 |
Did you repair a leak? | -- | Go to Function Test | Go to Step 10 | ||||||
10 | Replace the leaking actuator. Is the repair complete? | -- | Go to Function Test | -- | ||||||
