I'd start with the fuse and determine if you've got a good contact there.

Next I'd hit your defrost button and see if you get full speed, if you don't then you could have a blower motor that's about to die.

If it was the resistor, you'd lose the lower speeds and only have high speed.

Do you hear any squeaking sounds?

__________________
1989 300CE - 269,000 km
1994 SL600 - 59,000 km