A/C & HEATER MODULE OPERATION AND DESIGN CHANGE

MODELS AFFECTED: 1987 LESABRE & ELECTRA/PARK AVENUE WITH C60 MANUAL AIR CONDITIONING

NOTICE: The following infomation was not available at the time of publication of the 1987 Chassis Service Manual, Section IB. Therefore, it was not included.

Beginning in 1987, a new A/C and Heater Module was used on above cars. The new module employs an additional air valve called the slave valve. The slave valve is vacuum actuated. Checked vacuum is distributed through the rotary vacuum valve at the control assembly mounted on the instrument panel. Vacuum "switching" is accomplished in this valve based upon the selector mode settings.

If the green hose to slave door actuator is disconnected or pinched, maximum heater or defroster performance will not be achieved at maximum heater temperature door settings. Also, if a massive system leak occurs elsewhere or the supply vacuum (purple hose is pinched or disconnected) maximum heater or defrost performance will not be attained. Vacuum must be present at the slave valve actuator while in heater and defroster settings. If not, some air bypasses the heater unit and temperature is diminished by approximately 40-45 F, and maximum performance will be adversely affected, especially at extremely cold temperature; (for example, O F outside temperature could be as low as 100 F instead of the expected 135 F), see Figures I through 3.

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.