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

MODELS: 1988-90 C/K TRUCKS

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 89-T-93 DATED AUGUST, 1989 TO INCLUDE 1990 MODELS AND TO UPDATE SERVICE PARTS. ALL COPIES OF 89-T-93 SHOULD BE DISCARDED.

Some 1988-90 C/K trucks may experience an A/C pressure cycling switch failure. With the start of production 1989, a new pressure cycling switch (part number 3096605) was used on the C/K trucks. This switch was also released on Truck Service Bulletin 88-T-188 (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 the clutch will not completely disengage. Customers may comment about the 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 the correct Julian date - 9020 or later. The Julian date can be found on the bottom part of the switch (see 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 part number was changed. The new part number is 52457853.

NOTE THE JULIAN DATE FOR JANLk4RY 1, 1990 WOULD BE 0001.

After either replacing the pressure cycling switch, or veritying 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 switch, (see 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.

Important

DO NOT CHANGE COMPRESSOR, EVEN THOUGH THE CLUTCH DRIVER MAY BE DISCOLORED, UNLESS THE COMPRESSOR IS SEIZED. SERVICE PARTS INFORMATION

Part Number Description Quantity 52457853 Pressure cycling 1 switch

Parts are currently available through GMSPO.

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.