3 years ago when I bought my 523i '96 it had problems with A/C. In hot weather ~38 degree C if A/C turned on, the temp. gauge started indicating temps close to 120 degrees... there was no way to keep A/C on. In our own workshop (since I work as a auto parts salesman) they managed to get the auxiliary A/C fan to start, and even first and second stage running... Later I learned that in fact second and third stage were merged together electricaly... It worked that way for a couple of years untill the aux A/C fan motor died (three of the six magnets inside the motor got unglued and ended up grinding against the rotor, causing huge current consumption and eventualy blowing all the fuses that govern the three stages of the aux A/C fan). Having the motor replaced with a used one, together with the resistor assy, I observed that only (I guess) the second speed stage is active. The mannifestation of that fact is that the aux fan starts at about 94 degree engine core temp, runs for about 10-15 secs and shuts off for about 20-30 secs...
The normal way of operation would be that the first stage starts at 94, runs for all the A/C on period in silent manner, the second stage active at temps above 104 engine core degrees, and the third stage kicks in in extreme conditions such as very hot outside temp, towing or climbing very stiff roads...
Since the thermostat keeps the engine at 95 degrees, the first speed stage of the aux fan is supposed to run as long as the A/C is turned on...
Before replacing the aux fan motor, the engine core temp in summer conditions was allmost allways close to 100 degrees. That was (I'm sure) beacause of the fact that the A/C condenser wich is placed in front of the radiator was full of dirth that calcified in the cooling cells over the years, and not enough fresh air got through to the engine radiator....Nevertheless, behind the aux fan motor and behind the supporting frame of the aux fan assy, the clogging was total so I guess about 50% of the normal fresh air amount was getting to the engine radiator causing the viscous coupling to spin excessively and sound as a jet plane...
Today I got the wiring diags for the aux A/C fan and figured out what could be the cause of missing first and third speed stage.
The results of faulty aux fan operation are poor refrigerant efficiency and ineffective cooling of the engine.
Thank you. I expect opinions.