A/C - System Locks In A/C or Heat Mode

91chevy11

GMC NUMBER: 89-1A-138

GROUP: 1A Heating and Ventilation

DATE: March, 1991

CORPORATE
NUMBER: 161101


SUBJECT:
HVAC SYSTEM LOCKS IN EITHER A/C OR HEAT MODE

MODELS:
1988-89 C/K 1, 2, 3 TRUCKS

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 89-T-18, DATED JANUARY, 1989 TO UPDATE THE SERVICE PROCEDURE AND SERVICE PART NUMBERS. ALL COPIES OF 89-T-18 SHOULD BE DISCARDED.


Some 1988 and 1989 C/K trucks may experience a condition where the HVAC system will not come out of either the Heater or the A/C mode when another mode is requested. This condition is known as "Mode Lockup". Previously, a jumper harness was released to correct this condition. An improved mode door actuator has been released which no longer requires the use of the jumper harness and the need to cycle the system into defrost. This "Mode Lockup" is caused by corrosion on the actuator contacts and the new actuator will eliminate this corrosion. The new actuator will also be about two times faster, as well as quieter.

Figure 1:

SERVICE PROCEDURES, MODE ACTUATOR REPLACEMENT (Figure 1)

Remove

1. Battery ground cable.
2. Instrument panel compartment for access.
3. Electrical connection to the actuator.
4. Retainer and linkage.
5. Mode actuator.

Adjust

Adjust the Mode Actuator:

1. Install battery ground cable and electrical connection to the actuator.

2. Turn the ignition key to the run position and let the actuator position itself.


3. Turn off the ignition key.

4. Disconnect the electrical connection to the actuator and the battery ground cable.

Install

1. Mode actuator.
2. Linkage and retainer.
3. Electrical connection to the actuator.
4. Instrument panel compartment.
5. Battery ground cable.

SERVICE PARTS INFORMATION

Part Number Description Quantity
16141802 Mode Actuator 1

This new mode actuator has a blue background pressed on label with the part number on it. 1988-89 mode actuators will have either a white or yellow background part number label. Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: D1807

Labor Time: 0.5 hr.