COOLING FAN RUNS BATTERY DEAD (DIAGNOSTIC PROCEDURE)

VEHICLES AFFECTED: 1984-90 A-CARS, 85-90 C-CARS AND 86-90 H-CARS

THIS BULLETIN HAS BEEN REVISED TO MAKE CORRECTIONS TO SECOND AND THIRD PARAGRAPH.

If the above mentioned condition is encountered, and the cooling fan relay is found to have failed (the contact points sticking together), the cause may either be in the air conditioning system or the cooling fan temperature switch.

If the cooling fan motor is found to be operating within acceptable current draw limits (20 amps on low speed or 35 amps on high speed) start by checking the air conditioner high side pressure with the system operating. The high side pressure should be stable. If the high side shows a rapidly vibrating needle on the gauge, this will cause the A/C cooling fan pressure switch to cycle on and off as rapidly as the gauge needle is moving. This in turn will cause the relay contacts to arc and eventually weld themselves together leaving the fan in operation with the ignition key turned off. Sometimes this can be further identified by tapping the relay during the failure mode and seeing the fan turn off.

A defective fan pressure switch or an internal problem in the A/C system may also cause this type of failure.

Another cause of the relay failing may be a defective cooling fan temperature switch. This can be identified in the following manner. Using a test light hooked to the positive battery terminal, touch the other end of the light to the temperature switch located on the intake manifold. With the engine running, if the test light is found to flicker on and off rapidly, the lamp switch may be causing the relay to fail in a similar manner as the failure described above.

Once the cause of failure is identified and repaired, the cooling fan relay should be retested to determine if it is still in a useable condition.

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.