eddie jr

I have an 85 2.8 FB and the rad fan is not working properly with the ac pressure switch. The fan works as required with the motor temp swtch but stays on all the time if you plug the ac pressure switch in. If i unplug the pressure switch harnes and put a paper clip in there the fan turns off as it should. I have now tried 2 brand new pressure switches and when i plug in the harness the fan still runs all the time, The switches are aftermarket (four seasons and whatever the napa brand is) because GM does not make them anymore.

The switch seems to have continuity with the ac off (as it should) becuase the ac system is fully charged and otherwise working perfectly......although i guess it should still even with the ac system discharged.

Any idea what is going on here? I don't like running the fan all the time as i am sure it will probably burn out the motor fighting the air when going down the highway, yet i will fry my ac compressor if i leave it grounded.

thanks.

Maverick H1L

iTrader: (8)

You will NOT fry the compressor with the fan switch wires connected. There is an auxillary wire in the 2.8 harness that has a ring terminal on it that gets grounded in the case of no A/C so that the ECM will turn the fan on and off when it should (also in the 3.1 harness, the wires are blue).

Have you tried checking the resistance of the pressure switch WITH the engine running? I may be wrong, but I'm assuming you're checking it with the key off.

Service manual says, under "Fan Runs ALL the time", first disconnect the secondary switch in the cylinder head (pass side, not the driver's side). Replace switch if fan turns off (good luck, IDK if you can find one outside of the dealer and they may not have it). Failing that, pull the C/H FAN fuse out of the fuse panel in the dash. Check the green/white wire at the relay if the fan turns off for a short to ground. Failing that, replace the relay (swap the relay with one next to it, it has the black/red wire).

There are other things in the manual, but this should be a starting point...

eddie jr

It's not the compressor i am worried about, it is the coolant fan motor.

Thanks for all the info though. I did end up finding the problem, it turned out to be the harness connector for the pressure switch. THe terminals seemed to be stretched just enough that the tiny pin terminals weren't touching enough (the harness only goes on in one position due to the design). Now it works perfect again and comes on an off with the ac pressure and is otherwise off (except based on coolant temp of course.

thanks.

Maverick H1L

iTrader: (8)

Actually, I wouldn't worry too much about the motor... IDK how long the PO of my car (the 87) had the fan hot-wired to run all of the time the engine was running (jumped 2 wires at the relay) because he had either removed or knocked off the air dam, but the car apparently made it up here from Alabama fine, and for a couple years after that (and maybe before, IDK, like I said). It was years after I had unbalanced the fan blades, and fixed the wiring, that the motor started making noises when cold but was fine when warm (or up to full speed).