A/C NOISE 'MOAN' DIAGNOSIS NEW PULLEY INFO.

SUBJECT: A/C NOISE/MOAN DIAGNOSIS PROCEDURE

MODELS: 1988-92 C/K TRUCKS

Some 1988-92 C/K trucks with air conditioning may make a noise, often described as a moan. Although, the compressor must be engaged to hear the noise it is not usually a compressor noise, but a resonance created by the entire mounting, drive belt, and accessory system. This makes checking each area of the total system a necessity when addressing an A/C noise condition. The following is a suggested list of items to check in the most logical order assuming that the A/C functions normally i.e. cooling is as specified, no air flow restrictions through condenser or radiator, compressor cycling and system pressures are normal. If there is any reason to believe a malfunction exists a system performance check should be done before noise diagnosis begins.

SERVICE PROCEDURE

Verify that noise occurs only when A/C compressor is engaged.

Check hoses and lines for hard contact that may transmit noise to the cab.

Check belt and pulley condition, cleanliness, tension, and alignment.

Make sure all brackets are present and all bracket, generator, power steering, air pump, and compressor mounting bolts are properly torqued. Torque specifications for these components can be found in the appropriate service manual for the year and model vehicle being serviced. If the vehicle is a 1988 model with other than a 7.4L L19 engine see GMC Truck Service Bulletin 88-T-56 (Corporate No. 831203) concerning the addition of two pencil braces. If the vehicle is a 1988 thru 1991 with a 7.4L engine see GMC Truck Service Bulletin 91-1B-154 (Corporate No. 131208) covering the addition of a brace kit and an inertia ring if necessary.

If everything to this point checks good, and the vehicle is a 1988 to 1991, Nitrille hoses may be added to reduce noise transmission. Nitrille hoses are covered in GMC Truck Service Bulletin 91-1B-188 (Corporate No. 061201R).

If the above procedures have not sufficiently reduced the noise, an inertia ring compressor pulley P/N 6553148 may be installed.

PARTS INFORMATION

Part Number Description Quantity ----------- ----------- -------- 6553148 Inertia Ring Pulley 1

Parts are expected to be available on 8/24/92. In case of limited inventory, parts will be placed on 400 control to waive VIP surcharges. Only verifiable emergency orders will be accepted. GMSPO will make every effort to obtain parts. However, the part will be shipped premium transportation at the dealer's expense and all other order types will be placed on backorder until the 400 control is removed.

WARRANTY INFORMATION

Labor Operation: D4260 Labor Time: 0.5 HRS.

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.