NSKPhila

Driving my 2004 BLK500 W209 when I got a burning electrical smell from vents (no smoke), then AC fan stopped. Removed kick panel and lowered fan - no evidence of anything burnt, and fan started when key was turned on, but shut off after 20 seconds. Replaced fan and module - connected wiring and turned key on before rebolting motor - fan ran for about 20 seconds then shut off even though control unit showed fan as being on high.

Now thinking control unit needs replacing - any suggestions?

Agent-A01

Did you check the fuse/relay for corrosion?

NSKPhila

didn't think to since the fan starts each time I start the car, then shuts off after 20 sec
if it was the fuse, it wouldn't start at all

Agent-A01

Doesn’t have to be blown. You can have corrosion on it or the conducting medium and it will increase resistance.
That in theory should blow the fuse but not always.

Fan is overheating and shutting down.

Did you buy used? What part number did you replace it with?

HETPE3B

Did you check final stage resistor (if such a thing applies to Mercedes)?

NSKPhila

bought new one, whatever the parts book said
did same thing as one I took out

NSKPhila

there are no resistors.. there's a controlmodule which was changed