INOPERATIVE A/C COMPRESSOR REPLACE COMPRESSOR. GMC Truck GMC MD Conventional (C Model) 1990

SUBJECT: INOPERATIVE A/C COMPRESSOR OR COMPRESSOR CLUTCH (REPLACE COMPRESSOR/INSTALL A/C CHARGE LABEL)

VEHICLES AFFECTED: 1990 C5H, C6H, C7H

THIS BULLETIN IS BEING REVISED TO CHANGE THE PART NUMBER OF THE SANDEN A/C COMPRESSOR TO THE CURRENT PART NUMBER.

Some 1990 Topkick medium duty trucks may experience an inoperative A/C compressor or compressor clutch.

This condition may be caused by an inoperative pressure cycling switch, close compressor tolerances, resonance through the compressor at approximately 4000 RPM engine speed and/or a low Freon R-12(R) charge.

SERVICE PROCEDURE

1. To determine if the pressure cycling switch is the root cause, reference Product Service Bulletin 90-1-500 dated January 15/91. Replace as necessary.

2. If compressor is inoperative, replace with new P/N 1131915 (gas engines only). This compressor has a torque cushion on the clutch driver to dampen rotational vibration. On diesel engines use Sanden A/C compressor P/N 15628022.

3. On both gas and diesel engine systems, Freon R-12 (R) refrigerant charge has been revised to 3.25 lbs. (1.47 kg.). Install new A/C charge label (part number 6559185) on top of accumulator, as shown in Figure 1. Wipe old label clean and place new label directly over top of the existing label.

IMPORTANT: Do not remove the old label.

NOTE: If the system has been discharged, be sure the clutch cycling time is no more than four (4) times per minute.

SERVICE PARTS INFORMATION

Part Number Description ----------- ------------------ 1131915 HR6 A/C Compressor (gas engines only) 15628022 Sanden A/C Compressor (diesel engines only) 6559185 A/C Charge Label

Object Number: 77973 Size: FS

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.