Have a 2002 C230 kompressor. The A/C blows hot air. The heat cannot be regulated. Heat from the engine blows into the car. New thermostat was installed. Everything went wrong.
Hmm, don't know how a thermostat would make hot air blow when the A/C is on. There are 3 possibilities I can think of, 1) your a/c is not working, possibly a leak or low pressure and you are just blowing outside warm air in, 2) one of the many regulator valves that controls the flow of heat and a/c went bad, 3) your hvac dash controls went bad. The following document (large file) may help you understand how it all works and see if you can fix it yourself.
A/C and heat do not work 
Linear Mode
