HIGH A/C COMPRESSOR HEAD PRESSURES AT IDLE. GMC Truck GMC MD Conventional (C Model) 1990

SUBJECT: HIGH A/C COMPRESSOR HEAD PRESSURES AT IDLE

MODELS: 1990-93 TOPKICK/KODIAK VEHICLES WITH A/C AND DIESEL ENGINE

CONDITION

Some owners of 1990-93 Topkick/Kodiak trucks may experience high air conditioning compressor head pressures at idle. Head pressures may be high enough to set off the pressure relief valve at the rear of the compressor. Repeated pressure relief valve discharges may deplete the air conditioning system of refrigerant.

CAUSE

This condition may be caused by the accumulation of dirt or other debris on the front of the radiator at the intercooler. If air flow is restricted, compressor head pressures may rise as high as 420 PSI, and cause the pressure relief valve to release. Oil residue may be found around the relief valve area from the repeated releasing cycles of the relief valve.

CORRECTION

Remove the charge cooler to inspect the front of the radiator for the accumulation of debris. Refer to Section 6A9 in the Service Manual.

NOTE: It is not necessary to remove the air conditioning condenser to remove the intercooler.

If it is determined that air flow is restricted, the radiator should be blown out by high pressure such as water or air. With the engine shut off, direct the pressure from the engine compartment (fan side) side through the radiator toward the front of the vehicle.

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.