Engine Cooling

Cooling Fan Troubleshooting Guide

Cooling Fan Troubleshooting Guide

>Does anyone know how to trace electric fan problems? I have been told
>that it should always work with the a/c on, car running, and the button
>depressed for the hood light switch. Fuses are good. The leads from the
>dryer are not producing current.

The following is specific to the '86 MY.

The auxiliary cooling fan should run when either the water temp OR the freon temp (at the receiver drier) get high enough to trip the thermoswitches AND the hood switch is activated (hood closed position). If this doesn't happen:


1) Check Fuse #29.

2) Temporarily swap Relay XVIII with another Type 53 relay. Use caution in removing relays - they fit very tightly.

MORE THOROUGH TESTING (If the above tests don't help)

Operation: 12v flows thru the actuating coil of Relay XVIII, thru the black/green wire to the "thermoswitch cooling water" and (in parallel) to the "temperature regulator freon"; from these thermoswitches thru brown wires to ground point MP I or MP II. Thus, when either of the thermoswitches reach their trigger temperature and trip, the actuating coil of Relay XVIII is energized.

1) Start testing by taping the hood switch in the closed position. Check for 12v on the black/green wire at the freon switch on the receiver drier. (This is the smaller of the two switches - the mushroom-shaped switch is the low freon pressure switch that kills the A/C compressor when freon is low.)

2) If there is 12v present, short to ground. If the fan runs, the switch is bad or the freon isn't getting hot.

3) If the fan doesn't run, go to Step 9.

4) If there is not 12v present, check for 12v at terminal Q22 on the central power board.

5) If 12v is present, there is a bad connection between this point and the switch.

6) If 12v is not present, remove Relay XVIII and check for 12v at connection 86.

7) If 12v is not present, there is a bad connection inside the power panel or a problem with either Relay X or your ignition switch.

8) If 12v is present, the relay coil is bad. Replace the relay.

9) Check for 12v at connection 30.

10) If 12v is present short connection 30 to connection 87.

11) If the fan does not run, check for 12v on the red wire at the fan (Use caution - the fan may start at any time!).

12) If there is not 12v on the red wire, there is a bad connection between connection 87 and the fan.

13) If there is 12v at the red wire, check for 12v at the brown wire.

14) If there is 12v at the brown wire, the ground connection is bad.

15) If there is not 12v at the brown wire, the fan motor is bad.

16) If 12v is not present on connection 30, check for 12v on both small metal tabs on the top of Fuse 29 (without removing the fuse).

17) If there is 12v on one tab and not the other, the fuse is bad, and I told you to check it first, dummy!

I hope that this lets you find your problem.

Wally Plumley
928 Specialists

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