pa944red

Hello folks.

I've read Clark's write up and and have read many many posts and I still have not found what I was looking for.

The problem I am having is that my cooling fans work when I turn my AC on and that is it, no other time. The thermoswitch tests out fine and the cooling fan relay tests out fine. Any ideas why my fans do not turn when the car heats up or stay on after the car is shut off hot?

Thanks
Tom

V2Rocket

thermostat?

pa944red

OK, I'm still having issues.

I had a thermostat laying around and I needed to change my coolant anyway, so in went a new thermostat and I bled the system. This did not help.

So now I have a recently bled cooling system, new thermostat and all the electricals seem to test out fine but my fans still will not turn on when the car heats up but do turn on with the A/C, any more thoughts?

Thanks
Tom

Mike C.

It sure sounds like a thermoswitch problem. How did you test the switch?

Spidey944

According to my wiring diagram, fan opperation is directly controled by the coolant temp switch. I don't think they are that expensive, so I'd just replace it. There is also a fuse panel that has 9 fuses in it, that is listed only as "add'l fuse box" in my diagram. Fuse #5 controls the cooling fan relay opperation for the low speed fan.

My other question is, do both fans come on when you turn the AC on of just the right side fan? If it's just the right side fan, I would say that maybe the left side fan is seized up internaly or the motor is just plain bad. HTH and Good Luck!

951jamie

Test the fan and then make sure someone has not done some re-wiring for the fan leads.When I got my first 944 one fan was blowing and one fan was sucking.So after a wire diagram and some new wires it works great!!

pa944red

Mike C.- I tested the switch by checking the resistance after the car has sat overnight and it was infinite meaning it was open per Clarks write-up. I then checked the resistance after I drove the car to work when the radiator was hot to the touch and the dash temp gauge needle just below the last block and the resistance was zero.

SpideySlave944- I will check fuse #5. And yes both fans come on when I turn the AC on. And if I leave the fans on when idling the temp gauge will go down to a normal reading.

One other question, is the fans AC operation indepedant of the cooling fan relay?

Thanks
Tom

Mike C.

Tom, the fans are wired so that when AC is turned on both fans will run no matter what the state of the thermo switch (cooling fan relay bypasses it). Your testing of the switch indicates it is working. As such, it may be that the ground path through the switch is not completing the circuit. According to the schematic, there is a brown wire and a brown with white stripe at the thermoswitch. The brown is connected to ground which you can verify with a VOM or DVM (should be near 0 ohms). The other wire goes to one of the cooling fans. Just for the hell of it, you might try a jumper wire on the thermoswitch leads which should turn on the fans also.

82-T/A

This is GREAT information! Thanks for posting that. I had no idea...

I guess it makes sense... all the brown wires on my VW Bus are ground... I should have figured!


Todd,
2006 Pontiac Solstice
2004 Volkswagen Beetle Convertible (Wife's)
2002 Ford Crown Victoria LX-P74
1987 Pontiac Fiero SE / V6 (3.2)
1984 Porsche 944
1981 Pontiac Trans Am WS6 (Olds 455)
1973 Volkswagen Type-2 Transporter (1800)

Mike C.

Any time Todd. You could also run a jumper from the brown/white wire directly to ground which should make the fans go on. If they do then you know the problem is on the ground side of the thermoswitch.

82-T/A

Yeah, I'm going to check that this weekend. I'm really not sure where that solid brown wire goes to, but it appears to go back into the harness. If there's an issue there, I might just make a new ground wire straight from the core support.

pa944red

Here's an update.

When the thermoswitch lines are jumped, the driver's fan spin at the slow speed so all should be good there.

After that test I called the local parts store and to my surprise they had both the relay and the thermoswitch in stock and out the door for less then $25, so I bought both.

I installed both the relay and the thermoswitch and now all is good. I wish I had a clear cut reason as to why everything works now, but the original thermoswitch and relay still test out fine on my bench and in my wife's pot on the stove

If I would have known how cheap the parts are, I would have just replaced them to begin with because after all I was dealing with an electrical part that is potential 23 years old.

Thanks again for all the input, I'm sure someone down the line will be helped by this thread.

Now here's the really dumb question/comment of the morning. I noticed this morning when it was 30* how smooth my idle was during my commute. Anyway a bad thermoswitch could affect idle?

Thanks
Tom

Mike C.

Glad it worked out. Maybe just the connections to thermoswitch were dirty? I can't imagine how a new switch could have any effect on idle smoothness. If the idle is lumpy only when engine is cold I might suspect you're getting no cold enrichment. I'll have to dig to remember how that is supposed to happen on a 944...

Spidey944

if the switch is bad, the computer should richen the mixure up because it thinks the car is in Antartica instead of PA. Most temp switches default to -40 deg F when they go out. This could've caused your rough idle, but who knows.

pa944red

Just to be sure here, I am talking about the thermoswitch in the radiator. I did not realize that it communicates with the computer. I thought the computer received its temperature reading from the temperature sensor in the head.

Thanks
Tom