LOSS OF HEAT/COOLING CONTROL REVISED PROGRAMER AVAILABLE

Subject: LOSS OF HEATING OR COOLING CONTROL

Model and Year: 1991 CORVETTE WITH 5.7L ENGINE

Condition: On some vehicles the temperature of air coming from the HVAC system, with C68 option, cannot be changed. A code 01 or 02 may also be set in the HVAC control head.. The "auto" blower may read "O" speed.

Cause: The air mix door of the HVAC system will not move out of the full hot or full cold position, causing loss of heating or cooling control, because the mix motor has not recalibrated itself.

Correction: This condition may be caused by wiring disconnects, air mix door motor condition, Freon loss, or related A/C system conditions. If normal diagnostic procedures do not correct this condition, a revised A/C programmer is available. This change was made in production with VIN M5101083 (L98) and M5800130 (LT5).

Part Number Engine ----------- ---------------- 16140190 L98 (VIN Code 8) 16151009 LT5 (VIN Code J)

IMPORTANT: THE 1990 AND 1991 C68 PROGRAMMERS ARE NOT INTERCHANGEABLE.

Parts are currently available from GMSPO.

Use the procedure in Section 1C1 of the 1991 Service Manual to replace the programmer.

NOTICE: WHILE WORKING ON THE HVAC SYSTEM, DO NOT RUN THE AIR MIX DOOR MOTOR WHEN IT IS REMOVED FROM THE HEATER CASE. THIS WILL DAMAGE THE MOTOR.

Warranty Information: Use labor operation number D0780.

Use applicable Labor Time Guide for labor hours.

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.