A/C NOISE OR VIBRATION (PRELIMINARY INFORMATION)

SUBJECT: AIR CONDITIONING NOISE/VIBRATION

MODEL and YEAR: 1987-92 S/T TRUCKS WITH 2.8L ENGINE AND AIR CONDITIONING

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO.89-149-1B, DATED APRIL 1989. THE SERVICE PROCEDURE HAS BEEN UPDATED AND THE 1990-92 MODEL YEARS HAVE BEEN ADDED. ALL COPIES OF 89-149-1B SHOULD BE DISCARDED.

Some 1987 to 1992 S/T Trucks equipped with 2.8L engines may exhibit a moan noise or vibration when the air conditioning compressor is engaged. Some customers may express concern that this noise/vibration is a result of a malfunctioning A/C compressor.

The A/C compressor is a high pressure pump that transfers refrigerant thru the system. The normal pumping action of this compressor causes pulsations that are transferred and amplified thru various engine and body components resulting in the moan/vibration experienced by the customer. Higher ambient temperatures increase the pressure in the system resulting in stronger pulsations and increased noise/vibrations. Replacement of the A/C compressor will not eliminate this condition. This noise/vibration does not affect the efficiency or durability of the A/C system.

If the service technician's observation of the A/C system indicates that the system is operating as designed, provide the customer the "A/C System Operation Description" provided with this bulletin.

In the event that some customers, who operate their vehicle under high ambient conditions for extended periods of time, continue to find this noise/vibration to be objectionable, even after reviewing the "A/C System Operation Description", a modification is available that will dampen the pulsations emitted by the A/C compressor.

The installation of a brace kit (P/N 10115893), a high inertia pulley (P/N 6552544), and a Kevlar (tm) serpentine belt (P/N 10189266) may be required depending on the model year of the vehicle.

The brace kit was factory installed on all 1990 and later vehicles with the 2.8L engine and air conditioning. Vehicles built prior to 1990 will require brace kit installation.

The Kevlar (tm) serpentine belt was installed on 1992 vehicles with the 2.8L engine and air conditioning beginning with the VIN breakpoints listed below:

Moraine N2142041

Pontiac West N0122517

Shreveport N8148293

Vehicles built prior to these breakpoints will require the Kevlar (tm) belt.

SERVICE PROCEDURE:

Brace Kit Installation

1. Verify that Brace Kit has not been installed previously (Fig 1)

2. Follow installation instructions provided with Brace Kit (P/N 10115893).

High Inertia Pulley (P/N 6552544)/Kevlar(tm) Belt (P/N 10189266) Installation ----------------------------------------------------------------------------- NOTICE: Removal of the A/C compressor and system discharge is not required to make this modification.

1. Remove upper fan shroud to obtain clearance to remove compressor clutch plate hub and rotor.

2. Remove serpentine belt.

3. Follow instructions for clutch plate hub and rotor/pulley replacement in section 1B3 of the Unit Repair Manual.

4. Install Kevlar (tm) belt (P/N 10189266) if vehicle built prior to the supplied breakpoints.

5. Reinstall upper fan shroud.

SERVICE PARTS INFORMATION

PART NUMBER DESCRIPTION QTY/VEH ----------- ----------- ------- 10115893 Brace Kit 1 6552544 High Inertia Pulley 1 (includes bearing) 10189266 Belt, Kevlar 1

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

LABOR OPERATION DESCRIPTION LABOR TIME ---------------- ----------- ---------- T7415 A/C Brace Kit, Install .4 hrs

T7416 Remove and reinstall fan shroud, remove and replace Pulley/Rotor/Bearing .6 hrs.

A/C SYSTEM OPERATION -------------------- Air conditioning is accomplished through a heat exchange process which incorporates an engine powered pump/compressor.

The A/C compressor is a high pressure pump which forces refrigerant through the system. The compressor has rotating vanes which capture the gaseous freon and compresses it into a condenser. The rotating vanes give pressure surges or pulsations which result in a resonating noise that is transmitted through the engine and frame into the vehicle.

This noise is often called AIR CONDITIONING MOAN and is a normal vehicle condition. Higher ambient temperatures increase the system pressures resulting in an increased intensity of the pulsations and the accompanying moan. The durability of the system is not affected by this condition.

Replacement of the air conditioning compressor will not correct this normal condition but it will cause you the inconvenience of having your vehicle out of service.

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.