A/C NOISE/INSUFFICIENT COOLING REPLACE COMP. CYCLING SWITCH

SUBJECT: A/C NOISE/INSUFFICIENT COOLING/INOPERATIVE COMPRESSOR (REPLACE CYCLING SWITCH)

VEHICLES AFFECTED: 1990 C5H,C6H, AND C7H TOPKICK MEDIUM TRUCKS WITH AIR CONDITIONING (RPO C60)

Some of the above models with either Harrison or Sanden air conditioning compressors may experience an inoperative A/C pressure cycling switch. When this happens, the compressor clutch will rapid cycle or "flutter". This cycling will be so fast that the clutch will not completely disengage. Customer comments would be for the noise associated with the rapid clutch cycling, insufficient cooling due to clutch slippage, or for an inoperative compressor. Many times, however, these symptons will not be noticed and the switch will cause the compressor clutch to overheat and become inoperative, possibly seizing the compressor.

Effective June 4, 1990, the pressure cycling switch was changed in Production to part number #52457854. If the customer comments as above, or if the compressor becomes inoperative due to the clutch slipping or overheating, verify that the switch is the correct part number or replace it with the new switch. The part number is etched onto the body of the switch, as shown in Figure 1.

After either replacing the pressure cycling switch, or verifying that the switch is the correct part number and operational, the switch should be protected from water intrusion. To do this, electrical tape should be wrapped around the switch. Starting at the seal side of the switch, refer to Figure 2, wrap the tape around the switch so that one edge is flush with the accumulator. Slowly progress towards the wire side of the switch, overlapping each turn, until a full turn around the wire is completed.

SERVICE PARTS INFORMATION

PART NUMBER DESCRIPTION ----------- ------------------------ 52457854 Pressure Cycling Switch

Parts are currently available from CANSPO.

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.