Manual A/C Systems

DIAGNOSTIC TESTS

Control Knobs:

The manual air conditioning system (Non-ATC Systems) have built in self diagnostics. Use the following procedures to access and test the system. All diagnostic trouble codes will be displayed through the rear window defogger switch LED light.

NOTE: In order to perform any tests, the control head must be placed in its diagnostic mode.

To access the diagnostic mode perform the following steps:
1. Start the engine and allow it to run during the entire test. The vehicle must not be moving during this test.
2. The left knob (Blower control) must be placed to any speed setting. Do not place the knob to the off position.
3. The center knob (Temp knob) must be placed in the full cool position.
4. The right knob (Mode control) must be placed in the defrost mode.
5. The A/C button on the control head can be in the on or off position.
6. Press the rear window defogger switch and hold for three to five seconds. The rear window defogger switch light will begin to flash. Release the button when the light begins to flash. The system is now in the diagnostic mode. The following steps must be used to diagnose the system. To abort the diagnostic mode either:
- Turn the blower switch to the off position
- Push the A/C or rear window defogger button once
- Or change either the temperature selector or mode selector settings
7. When the diagnostic mode is first entered, the rear window defogger switch will flash for approximately 30 seconds. During this time the actuators are being calibrated and checked. If calibration is successful the light will go out. If the rear window defogger switch light has gone out, skip to Step 10 of this procedure. If the light remained on, continue with this test.
8. If there is an unsuccessful calibration, the rear window defogger switch light will remain on. This indicates that a problem is present in an actuator or there is an internal control head problem.
9. To determine where the problem in the system is:
- Move the mode actuator knob to the mix position. If the rear window defogger switch light remains on, this indicates that there is an internal problem with the control head. If the light goes out, the control head electronics are good.
- Move the mode actuator knob to the floor position. If the rear window defogger switch light remains on, this indicates that the blend door actuator wiring or HVAC blend (Temp) door has a problem. If the rear window defogger switch light goes off in this position, this indicates that the blend door actuator and circuits are good.
- Move the mode actuator knob to the Bi-Level position. If the rear window defogger switch light remains on, this indicates that the mode actuator and/or circuit has a problem. If the rear window defogger switch light goes off in this position, this indicates that the mode actuator, HVAC mode door and circuits are good. The recirculation actuator can be checked after completing the following control knob test.

CAUTION: Step 10 (mode actuator knob test) and step 11 (temperature knob test) cannot be performed if test in step 8 (unsuccessful calibration) occurs. One must fix problem of step 8 before testing mode and temperature knob operation.

10. To check the mode actuator knob perform the following:
- Run Calibration diagnostics.
- Place the mode actuator knob in the mix mode. The rear window defogger switch light should flash twice and then pause. It should continue this two flash sequence. This indicates that the mix mode has no problems.
- Place the mode actuator knob in the floor mode. The rear window defogger switch light should flash three times and then pause. It should continue this three flash sequence. This indicates that the floor mode has no problems.
- Place the mode actuator knob in the Bi-Level mode. The rear window defogger switch light should flash four times and then pause. It should continue this four flash sequence. This indicates that the Bi-level mode has no problems.
- Place the mode actuator knob in the Panel mode. The rear window defogger switch light should flash five times and then pause. It should continue this five flash sequence. This indicates that the Panel mode has no problems.
- Place the mode actuator knob in the Recirculate Panel mode. The rear window defogger switch light should flash six times and then pause. It should continue this six flash sequence. This indicates that the Recirculate Panel mode has no problems.
- Place the mode actuator knob in the Recirculate Bi-Level mode. The rear window defogger switch light should flash seven times and then pause. It should continue this seven flash sequence. This indicates that the Recirculate Bi-Level mode has no problems.
11. To check the temperature control knob perform the following:
- Place the mode actuator knob in the defrost position.
- Slowly turn the temperature control knob clockwise while observing the rear window defogger switch light. As you turn the knob clockwise the rear window defogger switch light should begin flashing. It will continue to flash faster as the knob is turned. Once the knob reaches full heat the rear window defogger switch light will go out.
- Switch the mode actuator knob between panel and recirculate panel and observe the recirculation door for movement. If the door moves correctly the recirculation door actuator and circuits are good.
- To exit the diagnostic mode either turn off the blower or push the A/C or rear window defogger button once.

NOTE: If the scan tool is to be used, refer to Automatic Temperature Control (ATC) System Testing and Inspection/Procedures.

Scan Tool Flow Chart:

This Scan Tool Flow Chart is a sample of the items that can be tested with the scan tool.

NOTE: The scan tool cannot be used to check the manual - A/C control or manual - A/C, HVAC door operations.