Radiator Fan...WTF???
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Audiworld Junior Member
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From: VT
Radiator Fan...WTF???
So, I just finished repairing all the front end damage to my '87 4kQ. Topped up the coolant and fired 'er up. Everything runs just peachy, except the radiator fan doesn't kick in.
Tested the radiator thermo switch. It goes to zero resistance at the proper temperature range and is open when cool.
When I short the thermoswitch wires, I can hear the relay clicking closed and I measure 14V at the fan connector on my DMM.
I plugged the fan into a 13V power supply and it spins up fine. Plug the connector back in and the fan doesn't run.
What the hell?
I removed the A/C stuff while I had the front end apart (winter beater). But I can't see anything in the Bentley wiring diagrams that would indicate that I could eff something up by doing that.
Tested the radiator thermo switch. It goes to zero resistance at the proper temperature range and is open when cool.
When I short the thermoswitch wires, I can hear the relay clicking closed and I measure 14V at the fan connector on my DMM.
I plugged the fan into a 13V power supply and it spins up fine. Plug the connector back in and the fan doesn't run.
What the hell?
I removed the A/C stuff while I had the front end apart (winter beater). But I can't see anything in the Bentley wiring diagrams that would indicate that I could eff something up by doing that.
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If you have power, how about ground? Check continuity for the fan ground connection. 2.5 brown wire in harness; on the later cars with the bigger fans that wire is fused to keep you from burning up the wiring harness if the fan draws too much current. Not a bad idea...
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From: VT
Yeah, I was going to start tracking down grounds next...although if I measured 14V across the fan connector when the relay is closed, you'd think the ground would be sufficient. Who knows. Electrical gremlins are always fun...
AudiWorld Senior Member
Joined: May 2010
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From: Colorado
If you unplug the wires from the switch at the bottom of the radiator and jump them together, are you saying the fan doesn't come on when you turn the key on but the relay clicks? It should definitely come on in that situation. If not then I would suspect either a bad relay (cracked solder joints) or a bad wire.
-Rog
-Rog
Thread Starter
Audiworld Junior Member
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From: VT
Yep, with the car idling, I can short the thermoswitch wires and hear the relay click. When the relay clicks over, I can measure 14V across the fan connector. If I plug the fan connector back into the fan, it doesn't run. If I use an external power supply to supply 14V to the fan, it spins just fine.
It's got to be a wiring/grounding issue...my favorite!
It's got to be a wiring/grounding issue...my favorite!
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fan connector
Another thing that can cause the connector to fail is the amount of tension on the harness; seems that Audi didn't want to spring for another inch of wiring, so sometimes there is constant tension on the connector.
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Thread Starter
Audiworld Junior Member
Joined: Sep 2010
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From: VT
Thanks for the tip re: the connector. Mine is purely a mechanical problem. In the accident, the radiator got pushed back slight and the plastic tabs that hold the connector into the metal housing of the fan motor were damaged. I didn't see any evidence of arcing or melting back there.
That wiring harness is a pretty tight fit, not a lot of strain relief there.
That wiring harness is a pretty tight fit, not a lot of strain relief there.
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