NO COOLING FAN OPERATION IN DEFROST MODE

NO COOLING FAN OPERATION IN DEFROST MODE (CONDENSATION ON WINDSHIELD AND/OR COMPRESSOR NOISE) INSTALL A/C PRESS SWITCH)

VEHICLES AFFECTED: 1984-88 "F" SERIES WITH A/C -----------------

Some 1984-1988 "F" models with air conditioning and the following engines may encounter condensation on the windshield and/or A/C compressor noise in defrost mode during engine idle or city traffic driving.

1984-85 L69 (VIN Code G) 1986-87 LG4 (VIN Code H) 1988 L03 (VIN Code E)

- The engine cooling fan does not run in defrost mode, but will run continuously in MAX, NORM, or BI-LEVEL mode.

- The A/C compressor is shut off at high A/C head pressure which can occur with low air flow across the condenser. With the A/C blower running, some moisture from inside the evaporator module may commence on the windshield.

- The occurrence of this condition is possible between temperatures of 50 to 80 degrees and 40% to 100% relative humidity.

The above conditions can be addressed by installing an A/C pressure switch in the A/C system and wiring it to the cooling fan circuit using the following parts and procedure.

Part Number Part Name ----------- --------- 14089590 A/C Pressure Switch * 12058922 Switch connector with pigtail wires colored dark blue and black

* Order connector kit, 12058917 to get the above connector.

Procedure

1. Disconnect the negative battery cable.

2. Install the A/C pressure switch in the liquid line pipe valve of the A/C pipe from the evaporator to condenser (See Figure 1 for location).

3. Locate and pull the cooling fan switch wire out of the conduit on the lower right hand side of engine. The cooling fan switch is located at the rear right hand side of engine, between #6 and #8 cylinders, above the starter motor solenoid.

4. Splice the dark blue wire of the pressure switch connector to the cooling fan switch wire. Tape the splice and reinstall the cooling fan switch wire in the conduit. Cut a small notch in the conduit for the breakout point of the dark blue wire to pressure switch and tape conduit on each side of breakout point.

5. Install a ground wire ring terminal on the end of the black wire of pressure switch connector and attach it to the sheet metal body ground connection located above the pressure switch near the battery.

6. Reconnect the negative battery cable.

7. Start vehicle, put the control selector in DEFROST mode and FULL COLD and check for cooling fan operation.

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.