Hi,

the aux fan will only come on when the high side pressure increases to a certain pressure. so I wouldn't worry about that right now. Anyway while driving with sir entering the front of the car, this will simulate the fan running. This could also however be associated with the system not having enough refrigerant. I'm not a fan of diy kits as you can do a lot of damage if not sure of what you are doing. By the way I'm in the refrigeration and air con business so I do understand these systems well. Anyway your first course of action should be to physically check the suction pipe.It’s the bigger one returning to the compressor, usually has the charging up-stand connected to it on BMWs.Once the system is running this pipe should be sweating but not frozen.Also the discharge pipe (small pipe from compressor to condenser) should be too hot to touch and the liquid line from condenser to the fan coil, should be warm to touch.So if the suction is warm of the discharge not too hot to touch, then it is reasonable to assume that you need refrigerant.When adding do so very gradually and wait for pipe to be as I previously described.This is old school stuff but can, with experience, work as good as using a gauge (especially if broken).One other point is that if the system is not operated regularly, then the o-ring seals can dry out and cause gas to leak.FYI the oil circulates around through the system along with the refrigerant. Regarding your compressor, I would doubt very much that it is faulty.It will either be working or very badly damaged.I hope this helps you a little.