seltech

I searched yesterday for a fix for my radiator fans that run on full from the minute I start the car to when I shut it off on my 95 audi 90. I found the ECT sensor was bad and replaced it. After replacing it and starting the car I was very happy to hear no fans running and my coolant temps came up on the gauge, I decided to take it for a spin to bring up the temp and make sure everything was ok.

Here is the funny part, the second I slammed the hood shut, the fans turned on full blast lol. Of course this bothered the sh@t out of me so I pulled the plug from the thermal fan switch and the fans stopped. Does this mean the thermal switch in the radiator is bad? Is there another way to test this? any help is appreciated and needed

Lago Blue

I haven't had this exact problen but I imagine you could leave your switch installed and meter it (for continuity) on the car to see if it was forcing your fans on.

maineman

fans started when you shut the hood indicates that there is ..........

loose wire ?

I would guess that when you shut the hood the thermal switch closed and started the fans.
You could check the continuity across the terminals of the thermal switch .
There are 3 wires ......
12 volt power,low speed and high speed.
Grab the connector at the thermal switch and wiggle it to see if that does any thing.

Also if the Ac is on i believe the fans run . Could be in that part of the system also.

For 25 bucks it may be easier to replace the thermal switch first and see what that does.
http://www.partsgeek.com/gbproducts/...ek+Google+Base
If you do replace the thermal switch be careful about air bubbles in the cooling system.
good luck

seltech

Ok thanks guys, I found a test procedure for the thermal switch a couple days ago on here, but of course I can't find it now. I'll just replace the switch.

I've also noticed if I hit the AC button the snowflake comes on the display for only a second then it goes away. Don't know if that is related or not. Perhaps a relay?

Under my hood cowl, i'm missing the relays for the rad fan (i'm guessing because I have the climate control unit) is that normal? is there another relay for the rad fans somewhere else?

Thanks for your help guys!

maineman

After thinking about it ,this is what I would do.
disconnect the plug from the thermo switch. The fan should stop.If it doesn't then it's not the thermo switch .There are 3 connectors in the plug. One is 12 volt,one is low speed and one high speed.
Once you've determined which is 12 volt then with the car running connect the 12 volt to one of the other terminals. The fan should start,then the other, the fan should start.If it does start then I am 99.9% sure it is your thermal switch.
good luck

maineman

you are looking for are probably behind the knee bolster below the steering wheel.

seltech

ok thnx Roland, I'll check it out during lunch.

fyi when i unplug the thermal switch, the fans stop. I'll jump those connections in the plug and see what the fans do

seltech

Ok so i pulled the thermal switch plug and it has 3 connectors

when I jump the outer 2 connectors, the fans come on full

when I jump the connector in any other combination the fans do nothing at all.

relay? or even worse wiring?

Lago Blue

You have isolated the switch. If your switch was cold at test time, then your thermo-switch is defective.

I think it works like this: the thermo-switch should not provide a route by which power can reach the fan motor when cold, then only partial power when really warm, and finally full power only when really hot.

It sounds as though your switch is stuck (or nearly always stuck re: hood-close) "on". Prior to a complete install, a similar test of a hopefully good switch's function can be confirmed by showing a different result. You may also heat up some water and test the functions at temperature. I use a DMM to measure temp. while I test a thermostat before it's install, for instance.

seltech

Yes the switch was cold. I'm a bit confused though, when I jumped the plug for the switch I could only get high speed fans, I thought if i jumped the switch differently I was suppose to also get low speed which I couldn't do. Unless its a resistance thing, where the 2 outer pins are high speed fan, and if the middle pin is also used it reduces the fans output?

Any insight on how the switch actually activates the 2 different fan speeds?