4RINGSx3

The radiator fan on my '90 Coupe Quattro (98K miles) is constantly running. Car had not been driven in a week (did have Battery Tender hooked up), thus engine was stone cold. After being away for a couple of hours discovered that the radiator cooling fan was running. Pulled the 30 amp fuse at position #5, this did not stop the fan + plastic surrounding the fuse had somewhat melted. Pulled the 30 amp fuse at position #20, this killed the fan. I've not investigated any further although can say that re-installing the fuse at position #20 starts the fan running again. Have not tried re-installing the fuse at position #5.
I've searched the forum for this problem and did find some discussion on this problem. Anyone have any BTDT on this problem? In advance Thanks for the input and pointing me in the right direction.

Rusty Spokes

A reminder that the low speed fan(s) are supposed to run with the A/C on..so be sure the A/C is off.

A defective fan thermo-switch in the radiator will cause the fans to run all the time. Unplug the connector on the switch and install fuse 20..see if the fans remain off.

The "low speed relay" is notorious for sticking too.

Your car may have an "after run relay" too. Could be an issue with the after run relay. But first....

According to the wiring diagrams fuse 20 powers the low speed relay and the after-run relay. The notorious low speed relay is in position 11. Try another known good relay, probably a standard Bosch 30 or 40 amp four pin relay. with fuse 20 installed. See if the fan operates normally.

4RINGSx3

Rusty Spokes,
Thanks for your reply, most appreciated. I can tell you the A/C was off (the car had not been driven for a week & I always shutdown the HVAC system after driving & shutting off the engine).
The wiring diagram you attached is for an 80 model. I do have the Bentley "Electrical Trouble Shooting Manual" which contains wiring diagrams for 80, 90 & Coupe Quattro. Will certainly be referring to that and direct attention to fan thermo-switch in the radiator.
Thanks again.

4RINGSx3

Does anyone know about availability of the "Fan Thermo Switch" referenced in the Rusty Spokes 11/26/17 response? Audi part number?
In advance, Thanks.

Rusty Spokes

Get a Wahler thermo switch part number 251959481K..about $16 from FCPEuro. Avoid other brands like Meyle. You can get the 251959481K from VW/Audi for about $50. Wahler will work just fine.

4RINGSx3

Think the problem is fixed. Installed a new relay (Audi Part #443-955-532-C) today and so far cooling fan doesn't run with engine cold and ignition off. Thanks Rusty Spokes for your help...much appreciated.

Thewidowson

Rusty is the man around here.