burnt smell using ac or heat

I thought my ac compressor was low on oil and smelled burnt when using ac with fan. Now I get the smell using heater fan. I think the fan windings are overheating. any suggestions?

does it smell sweet?

It smells like burnt motor windings. It doesn't smell like coolant

And there is nothing under the hood making that smell?

all the fan speeds work?

I should have added that it smells like hot or burnt motor winfinds, but the fan operates normally. I shut it off thinking I would start a fire. Also any idea of where or if I have a air cleaner associated with this fan

You mean cabin filter? What year?

yes cabin filter, 2003

Avalanch and silverado maybe. Suburban and tahoe maybe not.

Check this out for silverados
http://www.automotiveforums.com/vbulletin/showthread.php?t=357803&highlight=cabin+air+filter

Hay dude it seems dirty smell.