Here's the situation. Have a BMW X5 where the electric auxiliary radiator fan is kaput. These are a real piece of work. BMW decided to put a variable speed fan with electronics that is controlled by the computer in one of the hottest, worst places. Like a regular one speed fan isn't good enough. So, they Cost $300+, fail quickly and are a bitch to replace. So, been driving the suv without it and it works fine, except there is no AC when you're not moving at all.
This got me thinking. Might the regular belt driven radiator fan clutch be bad? As I understand it, these have some kind of clutch based on a viscous liquid or something, so that when it's cold, the clutch loosens up and the fan doesn't spin at full speed. When it's hot the clutch tightens up and the fan runs at full speed.
Question is, how can you test that? With the engine hot after being driven awhile and with it 75F outside, with the engine off, I can spin the fan blade and there is a little resistance, but it moves pretty easily. I'm wondering if the clutch is kaput and that's why the AC won't work at all when not moving?
In other cars I've had, the aux radiator fan was only needed if it was extremely hot, like if I drove the car at highway speed, then parked it with the engine running and it was 90F outside. Then the aux fan would come on. But the aux fan wasn't needed for AC to work on say a 80F day with the car not moving.
Any thoughts? Like how do you know if the fan clutch is good or not?