Diagnosis by Symptom

4-way Connector Pin Out:

1. Start vehicle and allow engine to warm up.
2. For two seconds, depress the DEFROST, FLOOR and AUTO buttons at the same time. The ATC control should begin to flash on and off.
3. During the Diagnostic Test perform the following symptom tests:
a. Do all display symbols and indicators illuminate?
b. Does the blower motor operate at its highest speed?
c. Feel the outlet temperature. Does it get hot and then cycle cold?
d. Does the air flow switch from DEFROST outlets and then cycle to PANEL outlets?

If you can answer NO to any of these questions, proceed to step 4, otherwise proceed to step 5.

4. If you answered NO to:

SYMPTOM (a):
The display symbols and indicators do not illuminate. Failure Codes are not displayed.

TEST:
- After self-diagnostic test is complete, select a mode that will display the malfunction.

ACTION:
- If the ATC system operates properly, and the display does not, replace ATC control panel computer.

SYMPTOM: (b):
The blower motor does not operate.

CAUTION: Stay clear of blower motor and power module (PM) heat sink. Do not run system for more than 10 minutes with PM removed from A/C unit.

TEST:
- Check all power module and blower motor connections. Use a voltmeter to test for 12 volts (ignition) at both ends of the fuse with ignition ON. If fuse is good, test the green wire at the blower motor connector for 12 volts (ignition) to body ground.
- With ignition ON, and the blower motor still connected, check for 12 volts to body ground on the black/tan wire of the blower motor two way connector.
- Check for 12 volts at the Power Module pin #4 (BK/TN).
- Check for continuity from the Power Module pin #3 (BK) to chassis ground.
- Replace the Power Module.

ACTION:
- If 12 volts is not detected, repair feed circuit.
- If 12 volts is not detected, repair wires of the blower motor or replace the blower motor.
- If 12 volts is not present, repair wire from the blower motor connector to the Power Module.
- If circuit is open, repair ground circuit of the Power Module.
- Replace the Power Module (power transistor open).

SYMPTOM (C):
The outlet air temperature does not become hot and then cycle to cold during self-test operation. Failure Codes are not displayed.

TEST/ACTION
- Make sure the blend-air door is properly attached to the actuator.
- If cold air is not discharged from the outlets, check the base A/C refrigerant system.
- Make sure heating operation works correctly, (water level, thermostat, heater hoses, heater core, etc.).

SYMPTOM (d):
Air does not flow from DEFROST outlets and then cycle to PANEL outlets during self-test operation.

TEST/ACTION
- Check linkages from the mode door actuator for binding.
- Check for proper door travel in the unit.

5. The computer will do one of two things:
- Will return to the control settings that were selected before the DIAGNOSTIC TEST was started. This means the test is over. If FAILURE CODES did not occur, and answers to questions (a), (b), (c), and (d) were YES, the entire system is operating correctly.
- The blower motor will stop and the computer will flash a FAILURE CODE number from O1 through 28. Record the number and then depress the PANEL button to advance to the next test. If the ATC control flashes one or more codes 23 to 28, the digits on the display will flash alternating zeros. If you do nothing, these codes will remain stored within the ATC control computer. If all repairs have been made and you wish to erase these codes, see Fault Code Diagnosis/Erasing Codes 23-28.

Repair all failure codes in the order that they have been indicated, and then retest the system. If any blend door test fails, all remaining blend door tests will be skipped. If any mode door tests fail, all remaining mode door tests will be skipped.

NOTE: Diagnostic Test can be stopped at any time by depressing any button other than PANEL.