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Sean_Ironstag · Joined: 12 May 2012 Posts: 51 Location: Houston

So, I've just noticed within the last day, or so, that neither one of my radiator fans are kicking on. Therefore causing my car to overheat, and for my temp gauge to act up.
One (the drivers side fan) used to come on, all the time. While the other (passenger side fan) would only kick on every now and again. Now neither of them are coming on, and I am trying to troubleshoot and figure out what it could be, but I could definitely use some advice.
Any and all help is, as always, much appreciated.
Thanks.
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77 Porsche 928 Martini & Rossi Championship Edition

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Do you have some wire to jump from the battery to the connectors on the fans?

If you can verify the fans work, then you can look at the wiring from the fans to the temperature switch on the radiator.

The switch can be tested in a pan of hot water a thermometer and a continuity tester.

If those work then it is on to the radiator fan relay the fuse and the ground bloom behind the fuse panel on the firewall.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

!tom · Posted: Tue Oct 09, 2012 1:56 pm Post subject:

Could also be low on coolant.
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78 924 NA
5-lug

Sean_Ironstag · Joined: 12 May 2012 Posts: 51 Location: Houston

Okay... So I ran power directly from the battery, to each fan, they both work when powered directly from the battery. So that takes the fans themselves out of the picture, as the problem.
I am so lost right now though. I really need help with this. I've been trying to do other troubleshooting, but nothing is panning out.
I've checked the ground bloom, all the grounds are securely connected.
I tried checking the fan and a/c relays, i hear the click when I power them directly from the battery, but all the guides Ive read about testing the relays are confusing to me. When I test the relay (while it's powered), between terminals 30 and 87, I get 0 ohms for resistance (like youre supposed to), but then the guides tell you to test the terminals A and B (and youre supposed to get 0 resistance there as well, while relay is powered), but there are no terminals labeled A and B on the relays... So I cant tell if they are good or bad, because I am not sure what to do. There are terminals 30, 87, 85, and 86. Help?
Also, I tried disconnecting the electrical connector from the thermofan switch, and jumpering the connections on the electrical connector. If I do that when the car is off, nothing happens. If I do it while the car is on, the drivers side fan will come on, but not the passenger side fan.
Also, my slow fan resistor is registering 15-20 ohms when I measure resistance on it. That could be a problem, maybe?
Oh, and if this matters, the a/c on my car does not work, never has since I bought the car. Just sayin'
Also, coolant and oil levels are good. So are my fuses, I believe.
Please someone help...
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77 Porsche 928 Martini & Rossi Championship Edition

Paul · Posted: Wed Oct 10, 2012 10:55 am Post subject:

Passenger side fan wiring is bad?

All the switch does is to provide a ground for the fan motors, so make sure the switches connector has a good ground.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Sean_Ironstag · Joined: 12 May 2012 Posts: 51 Location: Houston

Perhaps, but even the drivers side fan only comes on when I jump the thermofan terminals when the car is on.
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77 Porsche 928 Martini & Rossi Championship Edition

Paul · Posted: Wed Oct 10, 2012 11:20 am Post subject:

The fact that the fan runs when the connector is bridged with ignition is on indicates the relay and fuse are good.

The fact that it does not run with key off and the connector bridged and the fact that the resistor is not open indicates the wiring must be bad from or to the resistor.

I need to reference a 77 wiring diagram before going any further to verify both fans are supposed to run or if one is for A/C and one is for the radiator.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

!tom · Posted: Wed Oct 10, 2012 1:07 pm Post subject:

joejax · Posted: Wed Oct 10, 2012 10:07 pm Post subject:

I wonder if the Thermostat is sticking, I thought the temp gauge sensor is before the stat and the fan switch is after.

I don't trust my new temp switch too much, A/C is disconnected and I use the A/C knob to turn the fans on and off.
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I got nothin'
Uhhh...you got any pics?