Gang -

I've been trying to track down why my electric cooling fan doesn't function. I verified that the fan itself was OK and also the relay - that left the sensors. (1990 740 Turbo wagon)

It would appear that the pressure switch which is on a (vertical) refrigerant line by the firewall is not working. (It is NOT the one on the receiver dryer but below it and a little more to the rear of the car.) It is supposed to close (ground) when the A/C is running (I think). When I pulled off the leads and grounded the appropriate one the fan came on just fine.

The A/C runs fine but with it running this switch was still open.

Is there a question here you ask? OK, should this switch be closed pretty much anytime that the A/C is running? Or does it cycle on/off with the compressor? Seems to me that I need to have this replaced by someone qualified (certainly not me!) as it will involve opening the A/C lines to the atmosphere. Of course, I have no idea whether this is high or low pressure side and whether or not that makes any difference.

Any tips (including non-dealer part source) would be appreciated.

Thanks!

Bob