Mercedes Benz repair: hot air from defrost and dash vents, mercedes 450 slc, hot air

Question
My 1978 mercedes 450 slc has hot air coming from the defrost and dash outlets even when the system is off. Anything I can do as a do-it-yourselfer to fix  this problem?
Tnanks

Answer
chances are that a valve in your system is open to do the simple cooling system flush ,thermostsat change, then check your mechanical motor unhook the fuse that runs the fan then run the car if it continues to blow hot air chances are your fan needs to be replaced or the off switch has lost its contact.