I am after some help/confirmations in respect to a few Porsche 964 electrical problems I have
I have been working on the air and cooling systems for a couple of years now and thought that I had the problems sorted?
I then purchased from Tore Bergvill his Porsche OBD diagnostic interface to read fault codes using Scantool.
I purchased it primarily to sort out the constant activation of the ABS/FWD warning lights, but no faults are being reported – so now off to my friendly auto electrician sometime in the future.
The air and cooling systems have three faults and the main one which I am now attempting to resolve relates to the rear two speed fan temperature sensor.
With CCU fan speed set at either 2 or 3 and adjusting the temperature, the rear fan would only come on at high speed when the temperature **** reached the red dot.
Checked the temperature sensor with a multimeter and it came up with a value of 6.95. The forums state if the reading is infinitely then it is shorted out so I am assuming that mine could be OK?
Next to look at was the fan resistor (mine has been updated to the latest part number). I cleaned it up and returned it to the air duct. The thermo switch was in the closed position. My assumption is that it should be closed??
Still a fault.
Removed the relay and shorted out both high and low speed circuits and both fan speeds worked.
So benched tested the relay set at 12V. The two internal relays have a common feed which I have assumed is a positive supply and activation is by an earth supply from the CCU. The low speed was pulled in OK but not the high speed so I removed the cover, the high speed would pull in with some encouragement of my finger and would stay pulled in.
I then checked relays for the airconditioning two speed condenser fan and two speed oil cooler fan. I benched tested them, again the high speed relays did not pull in?!
Please, my questions are:
1. Is my assumption that my rear fan temperature sensor is OK correct??
2. Should the rear fan thermo switch be closed at room temperature??
3. Can I have three faulty high speed relays, is it possible????
4. Am I doing anything wrong?

 

I'm pretty sure you need to replace or reset the rear fan ballast resistor. It's located on the plastic pipe that runs from the fan down to the heat exchangers. Shouldn't take more than 5 minutes to change out. It's said that you can reset it by clicking something on the undeside of it but that didn't work for me and I needed to replace it.

 

The rear fan low speed resistor thermoswitch shall always be closed. However, most often the relay contacts in the switch are dirty and will not connect. I always change the resistor into new if there are issues with the thermoswitch when having cars in for service. You can check the resistor and switch with an ohmmeter on the terminals, you should read a very low value, 1 ohm or something.

I would advise to change the rear fan relay if any issues. Both this and the resistor are not very expensive, and I don't bother to try to clean or fix them.
Cheers,
Tore