Heater-temp or blower?
If you're getting warm air all the time but no blower motor sometimes when the engine is running and the blower normally will run with the key on but engine off, it may be the (oddly enough) ignition switch. Try jiggling the key, it may come on. Learned this through the search function here, would sell my car without this forum!!
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)