wrote in message
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Also, Ive been helping a friend with the FSU problem. His blower
went from working fine to not working at all. Being concerned about
all the apparently crap ones out there, bought one from a BMW dealer
that is marked Sitronic. It appeared to work, but..... With the
blower on high it will run all day, no problem. You can back the blower
off to about 80% and as you do so, the heat sink starts to get very
hot, but the blower still runs at 80%. If you back the speed down
anymore, it gets even hotter and then starts pulsating the blower,
finally stops all together. I tried dipping the end of the heatsink
rods into a container of water when it does that and within a couple
seconds the blower starts working again fine. So, it's definitely
heat related.

Any ideas on what's wrong? First impression would be that it's the new
FSU because the blower works on full or near full speed. But I guess
the other possibility is that the motor has a problem? Seems odd
though that a single winding type DC motor could run fine at full
speed, but then cause the FSU to overheat at lower speeds.

Could be the motor. While not exectally correct, the motor requires a
cretain ammount of power. When running at full speed the transistor is
acting more like a swithc. At slower speeds it is acting more like a
resistor. Any power that is not used to get the motor to speed is converted
to heat in the FSU. The slower the motor is ran, the hotter the FSU will
get. If the bearings are going bad or there is some other reason the motor
is drawing more than the rated current the FSU will heat up more than
normal, especially at slower speeds.

Have you checked the current the motor is drawing and made sure it is
getting the voltage it is suspose to at full speed ?



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