HVAC CONTROL HEAD LOCKS UP TEMP. ACTUATOR CLICKS NEW P/N

SUBJECT: HVAC CONTROL READ LOCKS UP/TEMP DOOR ACTUATOR CLICKS WHEN AT FULL COLD (REP. CONTROL READ)

VEHICLES AFFECTED: 1991 C/K, T/K WITH A/C (RPO C60)

Owners of some 1991 C/K light duty trucks or 1991 C5H, C6H, or C7H medium duty trucks with the electronic pushbutton HVAC control head may experience a condition where the vent arrows on the left of the display and the temperature arrows on the bottom of the display begin flashing and the control head "locks up" so that no changes in the HVAC system can be made. This is caused when:

1. The control head is placed in defrost and the temperature arrow is placed at a point between full hot and full cold.

2. The "Heater" end of the selector button and the "Hot" end of the temperature scale button are pressed so that the mode actuator motor and the temperature door actuator motor are operating simultaneously.

Other 1991 C/K trucks may exhibit a clicking noise from the temperature door actuator, which is in the blower motor area. This is caused when the temperature is placed in full cold, and the temperature door actuator clicks for 45 seconds due to receiving pulses from the HVAC control head for the same 45 seconds.

Important: One truck will not experience both conditions.

To correct either of these conditions, replace the HVAC control head with a new HVAC control head (P/N 16152129 - LD. or 16149268 - MD).

SERVICE PROCEDURE:

The procedure for replacement of the HVAC control head is found in section 1B "CONTROL ASSEMBLY REPLACEMENT" of the appropriate Service Manual.

SERVICE PARTS INFORMATION

Part

Number Description Application -------- ----------------- ------------------ 16152129 HVAC control head 1991 C/K 1,2,3 16149268 HVAC control head 1991 C5H, C6H, C7H

WARRANTY INFORMATION

Labour Operation: D0362 Labour Time: 0.3 hrs.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.