A/C Pressure Cycling Switch - Noisy/Insufficient Cooling
90chevy29Number: 90-305-1B
Section: 1B
Date: August 1990
Corp. Bulletin No.: 961202R
Subject: AIR CONDITIONING NOISE/INSUFFICIENT COOLING/INOPERATIVE COMPRESSOR
Model and Year: 1988-90 C/K TRUCKS
TO: ALL CHEVROLET DEALERS
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 89-228-1B, DATED AUGUST 1989. THE 1990 MODEL YEAR HAS BEEN ADDED, PART NUMBERS CHANGED AND THE SERVICE PROCEDURE UPDATED. ALL COPIES OF 89-228-1B 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 Dealer Service Bulletin No. 88-411-1B 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.
Figure 1:
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 (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 JANUARY 1, 1990 WOULD BE 0001.
Figure 2:
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 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 from GMSPO.