1990 560 sel

I own a Mercedes 1990 560 SEL. My problem is that my heat/AC stopped blowing. If I turn all climate control buttons off and let car sit several days and
then turn on defrost the unit will start up and both heat and AC will work for a short time (sometimes seconds other times minutes) and then shut down. Of course if I have the heat control buttons on and drive down the road at a good speed heat will come out of the vents but blower will not be working. When switching control buttons I do hear the compressor engaging even though fan is not blowing air. I thought it might be the blower moter or blower regulator or heater moter but I am puzzled becasue it will occasionally work. This happened last year the same way and them in summer it began working again and lasted almost the whole summer season and then shut down-Bizaare???? If anyone knows what this could possibly be I would really appreciate your expertise.
Thanks
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Most likely the fan motor is on the way out. Very common. To test this... put fan on high when it is not working... and then hit the passenger side lower dash hard... if fan comes on, then it is definitely the motor.
You should also change the fan fuse regardless of condition.
If above two doesn't work, then turn the ignition key back a bit more without shutting off the engine, if this work, then you need to change the ignition switch.
Above three are the most common solution to this problem.
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Tiger,
Thanks for the advice. I did all three. On high I hit the passenger side dash several times-nothing happened. I did change fuse. When I turn the key back the car shuts off. I am not quite sure of your explanation here. If you are right where is the fan motor located and how hard is it to get to?
Thanks
Tiger wrote:

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Not hard... The only thing hard is getting those bottom dash off and the ducts... Other part are easy.
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