R4 A/C COMPRESSOR NOISE (REPLACE COMPRESSOR)

VEHICLES AFFECTED: 1987 - 1989 LIGHT DUTY TRUCKS

Some 1987 - 89 light duty trucks, equipped with an R4 A/C compressor, may develop a condition described as a moan, vibration or noise when the A/C compressor is engaged. To address this condition Harrison Radiator has released a revised R4 A/C compressor (P/N 12338629) for truck applications listed below. The new compressor can be identified by a new model label. The new label has the model number printed in black with an orange background. In prior years the model number has been black with a gray/silver background.

IMPORTANT: The revised compressor alone will not solve all customer A/C noise comments. It is essential that the revised compressor 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 wear

Check that a brace kit has been installed from one of the following bulletins: 88-1-103 (corporate # 831203), 88-1-139 (corporate # 831209R), 89-1-116 (corporate 821202R) and 89-1-103 (corporate # 831211R). All are filed in group 1B.

NOTICE: Before insalling an A/C service compressor the oil in the compressor should be drained. All service compressors are shipped with 6 oz of oil. If the oil is not drained the cooling capacity of the A/C system will be severely restricted. If there is no evidence of leakage when the old compressor is removed: Drain oil from the old compressor. Measure the amount removed; if less than 1 oz. is drained from the old compressor, add 2 oz. to the new compressor. If more than 1 oz. is drained from the old compressor, add the same amount to the new compressor.

IMPORTANT: The R4 service compressor (P/N 12338629) is shipped with a green fan switch (located on the rear of the compressor). The switch is used only on C/K trucks, however, the switch does not have to be removed when this service compressor is used on other trucks as it does not interfere with the operation of the compressor. The 7.4 L G Van uses a red fan switch that must be transferred when this service compressor is used.

On the following trucks the compressor can be installed as shipped.

MODEL ENGINE ----- ------

1988 - 89 C/K ALL ENGINES 1989 R/V 5.7L, 7.4L 1987 - 89 G VAN 5.OL, 5.7L 1988 - 89 S/T 4.3L

On the following trucks before installing the compressor one or all of the following will have to be transferred: pulley, coil and/or clutch. Compare compressors before installation to assure that the electrical terminal is in the correct position.

MODEL ENGINE ----- ------ 1987 - 89 S/T 2.8L 1987 - 89 G VAN 4.3L 1987 - 89 M VAN 4.3L 1989 G VAN 7.4L

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.