INCONSISTENT IN-CAR TEMP. CONTROL (HEAT ASSEMBLY REPAIR)

Model and Year: 1986-88 CORVETTE COUPES ONLY

A new heater and air conditioning control head assembly has been released for production and service of the above models. This control head has a new calibration (software change) that determines and remembers the air mix door position.

This calibration feature runs the air mix door full travel (Full Cold position to Full Hot position) after start-up from a battery reset and remembers the size of the travel. The control then divides the measured mix door position by the full travel to obtain memory feedback for air mix door position. The time for the air mix door motor to travel full travel will be about 1.5 minutes.

NOTICE: THE BLOWER MOTOR WILL BE OFF FOR THE CALIBRATION TIME PERIOD (1.5 MIN.). THIS WILL BE THE ONLY INDICATION GIVEN TO THE OPERATOR OR CUSTOMER THAT THE CALIBRATION FEATURE IS IN PROCESS.

- If an "open" in the air mix door motor circuit is repaired, it will cause the system to recalibrate.

- Any work done on the air mix door motor should be followed by a battery or control head electrical disconnect/reconnect to cause a recalibration process to occur.

The new control head service part numbers and the VIN breakpoints for production vehicles with new control head are as follows:

Part Number VIN ----------- --- 1228824 J5113626 C68 A/C with C49

1228825 J5115928 C68 A/C without C49

These new control heads can be used on vehicles prior to the breakpoints to address reported conditions of inconsistent in-car temperature control. This however, should only be done if the customer has commented on a poor in-car temperature condition.

Use applicable labor operation and time.

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.