A/C NOISE/INSUFF./INOP COOLING REPLACE PRESS. CYCLING SWITCH

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

VEHICLES AFFECTED: 1988-90 C/K TRUCKS

This bulletin is being revised to include 1990 models, change part numbers and to update the service procedure.

Some 1988-90 C/K trucks may experience A/C pressure cycling switch failure. With the start of production 1989, a new pressure cycling switch (P/N 3096605) was used on C/K trucks. This switch was also released on Product Service Bulletin 88-1-157 (Corporate Number 861207R) as a fix for a noisy cycling switch. Sometimes, the pressure cycling switch has difficulty cycling the compressor clutch at the low set point. When this happens, the compressor clutch will rapid cycle or "flutter". This cycling will be so fast that clutch will not completely disengage. Customers may comment about noise associated with the rapid clutch cycling, insufficient cooling due to clutch slippage, or an inoperative compressor.

Effective Julian date 9020 (1989, Jan. 20), the switch design was revised to correct this problem. If a customer reports A/C noise, insufficient cooling or compressor failure, the pressure cycling switch should be checked for correct Julian date -- 9020 or later. The Julian date can be found on bottom part of switch (Figure 1). If incorrect, the switch should be replaced with one that has a Julian date of 9020 or later. Effective Julian date 0052 (1990, Feb. 21), the switch diaphragm seat was revised and the P/N was changed. The new P/N is #52457853.

NOTE: THE JULIAN DATE FOR JANUARY 1, 1990 WOULD BE 0001.

After either replacing the pressure cycling switch, or verifying that the switch is the correct Julian date 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 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.

IMPORTANT: DO NOT CHANGE COMPRESSOR, EVEN THOUGH THE CLUTCH DRIVER MAY BE DISCOLOURED, UNLESS THE COMPRESSOR IS SEIZED.

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.