a/c compressor clutch - aux fan resistor fixed

[joleonie]

Hello all, I just got a 1990 735i, 123,700 miles on it. Yesterday I noticed clicking sound as I was turning the fan on and off (a/c switch in the off position). I checked the compressor clutch and I can see that it's turning the compressor and it's on for as long as the fan is on, does not matter if the a/c switch on the control panel is on or off. I have one of those a/c control panel with 3 sets of switches underneath the three wheels to control temperature and fan speed. My question is, is the compressor turned on the same time the fan is on or do I have a problem with the a/c? Thanks for your input.

[shogun]

The aux fan comes automatically on in low when the AC is switched on = compressor runs. It goes on high speed, in case the temperatur sensor switch detects a too high temperature in the coolant, usually the switch at the radiator switches to high at 99 degree C, see here http://www.nmia.com/~dgnrg/page_20.htm
The aux fan should not come on automatically at low fan speed , when the aircon is off, only when the lower temp limit is reached. If it runs in high but not low, then the ballast resistor could be blown.

In case you pushed the right button of the 3 in the middle = AUC (the one next to the red arrow) http://bmwe32.masscom.net/johan/ihka...emp_sensor.jpg
then the aircon is also on, even if the aircon button is not pushed. This is to remove moisture from the air when no fresh air is coming in.

[joleonie]

Thanks Shogun for your reply. I got to play with the a/c last night and all seems to be working as you described except for the aux fan in front of the radiator. It does not come on at all so I may have a problem there. I will have and update as soon as the fan has been looked at. Thanks again.

[joleonie]

I took a look at it just a while ago and found out the resistor is blown. It runs on high but not on low and a resistance check on the resistor confirms it's bad. Thanks again for your help Shogun. I need to find a replacement for it.

[shogun]

here plenty Auxiliary Fan Resistor Repair Kits , prices are starting from $18.50 http://www.pelicanparts.com/catalog/...ELSWCH_pg2.htm
also pull the relays and spray the relay spades and also the connector pins at the fan with a good contact enhancer, have found on my 750 and a friends car the contacts oxidized and the aux fan did not work, after using contact cleaner/enhancer it worked again.

[joleonie]

Update: Installed the resistor today and the aux fan is now working as it should on low speed. Thanks for the help as always.