Why Does Heater Fans Runs All Night /'01 540i

[Herr Leber]

My climate control in my '01 540i works fine except the heater blower cycles on and off at night. Rhe first cold night here in the northeast resulted in a dead battery. Original battery I might add (probably due anyway for change).

The outside temp sensor was damamge after sloppy body work. I thought this may effect the heater fan operation but not sure. I disconnected the sensor but no effect on heater fan. I am tired of disconnecting the battery each night.

Any thoughts folks??

Thanks in advance,
Pat Leber

[Jeron]

Apparently the final stage resistor of E39's can cause this problem. (On E36's and E46's it only causes fan speed problems.)

http://www.bmwtips.com/tipsntricks/Fuse/heaterblower.htm

http://bimmer.roadfly.com/bmw/forums/e39/8114851-1.html

http://www.540i6.com/finalstagereplacement.html

[Herr Leber]

Thanks for the reply Jeron. I'll give a shot once I grab the part.
It'll be nice not having to disconnect the battery every night!

[Herr Leber]

The job is done and working fine.

The old unit did not want to come out without a fight however. The wiring disconnected uneventfully and the bottom retaining clip released pretty easily. I did have trouble from there as the unit did not want to come out more than a centimeter or so. It must have listened after a few choice curses.

Thanks again for the assistance.