jgalfo

My'86 has two cooling fans. they both work on temperature when the engine gets to 238* they turn on and cool the car down.

the problem is that when I turn on the AC neither fan runs. the AC compressor runs and the AC works fine until you come to a stop and because there is no fan running with the AC it stops blowing cold air even though the compressor is running.

I'm thinking that one of the AC pressure switches is going bad but then the compressor still runs fine. whe I ground the fan wire from the temp switch on the drivers side of the block the fan runs fine.

any Ideas?

on my other car as soon as you turn the AC on one of the cooling fans run to pull air through the condensor so you get cold air when stopped.

all help is appreciated

John

Mtn Billy

I think someone changed the fan system. Not too sure on that though. My 86 FSM shows one fan in the engine compartment and a A/C condenser fan in front of the radiator. I'll upload the schematic in a bit.

pcolt94

A wiring change might be a possibility. From what is see on the schematic I have, one fan comes on commanded by the PCM, and the other fan comes on commenced by the temperature switch.

If they paralleled both fans off the temperature switch, then whey will run together. But the PCM will be commanding nothing since it might have been disconnected. This would have been the command when you turn on the A/C which then tells the PCM to turn on one fan.

jgalfo

that is exactly what I have. one in front and one after the radiator. neithor runs with the AC turning on.

jgalfo

what is the PCM? the computer? please explain.

thanks,
John

Mtn Billy

Heerrree's Mtn Billy

Mtn Billy

Do you need circuit info?

pcolt94

PCM - Powertrain control module. Sometimes called ECM (engine control module).
Some cars are different, it can be confusing as GM has changed it in certain years and schematics don’t always follow either.

Cliff Harris

In '86 the fan behind the radiator is controlled by the ECM (PCMs didn't come along until later years). The ECM turns on the fan when the coolant reaches 228°F. It also turns on the fan if the HVAC pressure switch senses pressure in the system (which is obviously there if the AC works). Check this switch (the one with the small connector):



It's normally closed and opens with AC pressure, so unplugging it should cause the fan to come on.

The fan in front of the radiator is controlled by the thermal switch in the driver's side head between spark plugs #1 and #3. It turns on at 238°F. You can test it by unplugging the connector and shorting it to ground.

jgalfo

thanks all for this great information.

I am going to trouble shoot using this info and let you know what I find.

what a great forum

thanks,


John

SunCr

Only the Main Fan (behind the Radiator) is used for a/c on this Year. The switch opens at about 220 psi. After the charge is cooled and the pressure drops, it will reclose at 170 psi and the fan will turn off. If the system is low on gas or if the outside air temp is below 50 degrees, it won't reach the threshold for fan operation. You start your troubleshooting by disconnecting the Switch. If the Fan comes on, wiring and ECM are ok. From there, hook up a Manifold Gage set to see what the High Side Pressure is. Anything below 200 psi, above a 50 degree ambient, there's some other problem.

jgalfo

thanks. I will try this first. uplug and if the fan runs it is a low ac pressure if it does not run it could be the fan.

thanks,
John

SunCr

Pressure could be fine - you need gages to show you - if it's right, all you need is a switch.

jgalfo

thanks I'm going to try this friday

John

jgalfo

I unplugged the switch and the fan immediately started running. went to the auto parts store to purchase another switch and ran into a problem.

the old switch has an R12 base (small diameter) I have converted my car to R134. (larger diameter) I didn't realize this until I tried to install the new switch and it did not fit.

I went back to the autoparts store with the old witch in hand and they ordered me a new switch based on the cross referenced number from the body of the switch. I should get it saturday am.

Question: will the new switch be ruined because I am running R134?

thanks for the help so far I am closer to the fix

John

SunCr

No - but the switch shouldn't be any different for either gas and though a switch with a lower threshold for fan operation would be nice (for an R134 conversion), none exists. It's timed to open and turn on the fan with the high side in the 220's. I think they gave you the wrong part. I know a Dealer carries the correct one.

jgalfo

I got a new switch Saturday from O'Reiley's auto parts and it works like a charm.

thanks very much for the help.

you guys were right on with the advice!

John