Steven Harper

Just want to make sure my logic is sound. I had the fan final stage rebuilt and it is only turning on the passenger side fan. Both fans work when jumping the wired in the harness so I know they are good. I tested the signal at the harness from the controller by the passenger seat when jumping wires there and got the same 12 volt reading for both so I believe that part and the wiring are fine. My previous output stage (that UPS lost) only ran the drivers side fan which lends more credibility to the first stage and wiring being fine. With all this, I believe the rebuild is faulty. It is a used unit that didn't run either fan before the rebuild and now only runs one. Does this seem logical to the electric gurus out there?

Alan

Your logic may be flawed depending on what you did. You need to test for voltage on the feeders under load - so while you are driving the fans directly from these sources. Its possible to have apparently good voltage that collapses under load.
Its also possible that the "logic" part of the fan controller (the one by the passenger seat) has an issue and the final stage is good - but the logic controllers are usually reliable.

Alan

Steven Harper

This was all with the engine cold. I ran a jumper wire from pin 4 to pin 6 and 4 to 8 at plug #1 of the controller. 4 to 6 ran the passenger fan but 4 to 8 was nothing. I again ran the wires and tested voltage at the corresponding plug (pins 6 and 7) at the final stage and got 12 volts on both. So it seems the controller is sending the same signal to the final stage, but maybe I'm wrong. The original final stage (UPS lost it in shipping to be rebuilt) did the complete opposite and ran the drivers side fan. The replacement stage wouldn't run either fan so I sent it for a rebuild and now runs just the one fan.

PC-85-928S

Who did the rebuild?

Alan

The easy way to test the feeders under load is to monitor the feeder at the fuse output while trying to drive the fans (normally). So for your year Fuse 28 & 29. The ATC/ATO fuses have dimples on their face above & below the printed or embossed fuse rating - these allow probing the fuse blades while they are installed. For '85 - '95 cars the top of the fuse is the input and the bottom the output (use a ground on the ECU frame or similar). Test the fuse output voltage while under load, if that shows a major drop - also test the fuse input to verify the fault isn't upstream.

Alan

Mrmerlin

In addition to Alans great advice,
these are some of the things I have found while troubleshooting various fan systems

NOTE most probable fan issues are caused by poor connections to the fans via the fan plugs,
and the CE panel fuse connections.
I suggest to put D 100 on all the fan connections and fuses,
and replace both of the fan fuses with new hi quality fuses.
Then start testing.

NOTE make sure the fuses have discernible tightness upon insertion,
if the blade feels loose add some solder the fuse blade to increase the thickness.

Pay attention to the possibility that water has been dripping from the bottom of the blower box seals onto the top of the CE panel,
and corroding the contacts if thats a suspect,
then disconnect the battery then drop the CE panel and spray all the wire connections relay connections and fuse sockets with D100.