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I've been having trouble with my cooling system operation ever since I got my 951. First the fan would run all the time even with the key off, then the high fans started to not work at all so the car would overheat if it was driven to hard. I replaced the cooling fan relay after the car fans started running with the key off and that seemed to help for a bit (coincidence??).
So I bought a new thermofan switch and took the old one out. While I was there I tested the cooling fan relay's by jumping the terminals on the thermofan switch connector per Clarks Garage procedure and the relay passed all tests so it seems to be working.
To me this meant that it had to be the thermofan switch that was bad so I installed the new one (Which I might add was not OEM but some off brand that made the switch for an Audi. But they stated it would also work in my Porsche 951). But now the cooling fans don't work at all where with the old switch the fans would turn on at low fan speed at least.
So I removed the switch, put the old and the new in boiling water side by side to compare and tested continuity as follows.
This is the new switch, there is complete continuity between all three terminals on the switch at 200F. Is it supposed to be like this?
Should the switch be completing the circuit for both low and high fan speed at the same time? Anyways furthermore it seems like both circuits for low and high fan speed seems to turn on and off at the same temperature.
Where as the old switch only shows continuity between terminal 2 and 3 which is for low fan speed, at 200F.
This was the maximum boiling temperature it seems at my elevation.
Assuming you have the stock thermofan switch, you should get connectivity between pins 2 and 3 at 92C. Then as you heat it to 102C, then you'll get connectivity between pins 1and 3.
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Testing Thermofan Switch Continuity.
