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Re: heater fan trouble-shooting
... chances are either the blower motor driver is dead, or (more likely) the brushes on the blower itself are gone. This is one of the universal Audi 5k climate control problems (the other one is the recirc flap door actuator breaking away from its mount). I've done a couple blowers on different cars now ... let me give you my $0.02. All this information is available from the archives, and perhaps soon from the QFOM (?).
You will probably be able to extract a few more months of life from your blower motor by pulling off the plastic cover in the air plenum under the hood and then removing the rubber L-shaped duct that goes from the blower housing to the motor. If you look through the hole you will see the keeper for the brush's spring. If you push down on this keeper with a small screwdriver you will increase the spring's pressure on the brush and it should work a little better. You can test to see if this is your problem by rapping on the body of the car at the base of the windshield near the blower with your fist with the A/C on and the fan not running ... if this causes the blower motor to start up, then you might benefit by increasing the spring pressure ...
I think I remember Ti Kan recently posting that there was some sort of thermal switch in the path to enabling the blower. I'd never known this before, but if you have a situation where the blower works reliably once it has started this may be your problem.
If you do decide that you need to remove the blower motor, I'd recommend that you attempt to remove the blower housing before attempting the highly recommended "steak knife" method. There is a strap that holds the box down and a couple hard plastic brackets that are screwed into it from the driver and passenger footwells. Once you release the Bowden cable you can try to lift the box up. Chances are the gasket has aged to the point where you can easily lift the blower housing enough to access the 3 screws that hold on the access cover. If the seal is still in good shape then you may not be able to lift the blower box very much ... NOW you can go ahead with the steak knife if you wish ... You will find the blower motor will come out without too much coaxing, but sliding in the new one can be a real PITA. I lube the housing with silicone spray and it slides right in ...
San Jose, CA (USA)