AIR COMPRESSOR MOAN/VIBRATION OR NOISE. GMC Truck GMC K Pickup

SUBJECT: A/C COMPRESSOR MOAN/VIBRATION/NOISE (INSTALL SUCTION-DISCHARGE HOSE ASSEMBLY)

VEHICLES AFFECTED: 1988-91 C/K TRUCKS WITH A/C (RPO C60)

THIS BULLETIN IS REVISED TO INCLUDE THE 1991 MODEL YEAR AND ADD INFORMATION ON THE 1992 MODEL HOSES.

Some 1988-1991 C/K model trucks may develop a condition described as a moan, vibration, or noise when the A/C compressor is engaged. To address this condition, a suction discharge hose assembly has been released for service. This new hose assembly will be made of a different material, (nitrile), than the production assembly and dampens more vibration. 1992 models, although not equipped with nitrile hoses, are equipped with hoses made of a material with the same vibration transmission properties.

IMPORTANT: The revised hose assembly alone will not solve all customer comments. It is essential that the revised service hose be used only after the following noise abatement procedures have been employed.

* Check A/C system for grounding (hoses/pipes hitting hoses/pipes, body or engine).

* Check mounting bolts for being loose, missing, or a blind hole.

* Check drive belt for debris in the grooves or for wear.

* Check that a brace kit has been installed from Product Service Bulletin 88-1-108 or Product Service Bulletin 91-1-150.

* Check that the latest R4 compressor is being used. All 1990and 1991 Model C/K trucks were built with the latest style A/C compressor. When repairing 1988 and 1989 model C/K trucks, reference Product Service Bulletin 89-1-145.

* To determine whether the new nitrile hose assembly will lessen the A/C noise-moan-vibration, have a person in the' cab listen to the noise at the engine speed where the noise is most prevalent. Have another person in front of the truck grab the suction hose with both hands. This will approximate the noise reduction which will result from replacement of the hose.

SERVICE PARTS INFORMATION:

Nitrile Hose Assembly

Part Number Application Quantity ----------- ----------- -------- 15551664 1988-89 C/K with LB4 (4.3L V6) 1 15551665 1988-89 C/K with L03/L05 (5.0L or 5.7L V8) 1 15551666 1988-89 C/K with L19 (7.4L V8) 1 15551667 1988-89 C/K with LH6/LL4 (6.2L V8 diesel) 1

15551668 1990-91 C/K with LB4 (4.3L V6) 1 15551669 1990-91 C/K with L03/L05 (5.0L or 5.7L V8) 1 15551670 1990-91 C/K with L19 (7.4L V8) 1 15551671 1990-91 C/K with LH6/LL4 (6.2L V8 diesel) 1

For vehicles repaired under warranty use:

Labor Operation: D-3088 Labor Time: 0.4 Hours. Add: 0.5 hours (C-discharge/charge A/C system)

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.