Use the diagnostic table below in order to diagnose the system if the following conditions exist:
| • | The airflow through the vents changes modes while driving. |
| • | The airflow through the vents remains in any mode and is unable to change. |
Refer to the vacuum diagrams and the operational charts for the following information:
| • | Airflow |
| • | Air door functioning |
| • | Vacuum circuits |
Inspect the hose connections at the following positions:
| • | The vacuum actuators |
| • | The control head valve |
| • | The vacuum tank |
If the vacuum is less than normal at all positions, remove the tee.
Connect the vacuum gauge line to the tank.
Read the vacuum. Refer to the following list for information on the vacuum readings:
| • | if the vacuum is still low, the problem lies in the feed circuit to the tank or the tank. |
| • | If the vacuum is now normal, the problem lies downstream. |
| • | The vacuum may be less than normal at some positions. |
| • | If the vacuum is low at one or several of the selector knob positions, a leak is indicated at the circuit(s). |
| • | The vacuum may be normal at all positions. |
| • | The malfunction may be caused by improperly connected or plugged lines. |
| • | If the vacuum is normal and even at all positions, the malfunction may be caused by the vacuum valve(s). |
Inspect the specific vacuum circuits using the following steps:
- Place the selector knob in the malfunctioning position.
- Inspect the vacuum for the pertinent vacuum actuators.
- Inspect the vacuum harness first.
If the vacuum exists at the actuator but the door does not move, the actuator is defective or the door is mechanically bound.
Determine whether one of the following is the cause:
| • | The vacuum harness |
| • | The vacuum valve is low |
| • | No vacuum exists at the actuator |
Inspect the vacuum harness circuit using the following steps:
- Disconnect the vacuum harness at the control head.
- The green line should show the engine vacuum. If the green line does not show the engine vacuum, trace back through the connector to the vacuum tank.
- Place the selector knob at the involved circuit position in order to check any individual circuit.
- Inspect for vacuum at the individual circuits.
Step
| Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Is the system stuck in defrost or the system changes modes while the vehicle is driving? | -- | Go to Step 2 | Go to Step 2 |
2 |
Does the vacuum drop immediately? | -- | Go to Step 3 | Go to Step 4 |
3 |
The reading should stay steady and momentarily stop the engine in each mode. The system should hold a vacuum in each mode for at least 20 seconds. Does the system hold a vacuum in each mode for the specified time interval? | 20 seconds | System OK | Go to Step 5 |
4 | Replace the hot water vacuum switch. Is the replacement complete? | -- | System OK | -- |
5 | Does the system hold a vacuum in any mode? | -- | Go to Step 6 | Go to Step 7 |
6 | Does the system hold a vacuum in only one mode? | -- | Go to Step 8 | -- |
7 |
Refer to Vacuum Tank Replacement Is the replacement complete? | -- | System OK | -- |
8 |
Do you hear any leaks? | -- | Go to Step 10 | Go to Step 9 |
9 | Apply 15 inches of vacuum to each port at the rotary vacuum switch harness. Does the system hold the vacuum? | -- | System OK | Go to Step 11 |
10 | Replace the control assembly. Refer to Control Assembly Replacement Is the replacement complete? | -- | System OK | -- |
11 |
Is the replacement complete? | -- | System OK | -- |
