I have a 82 300SD that provides heat sporadically. On cold days, it does not heat constantly. On those days the temperature in the car never reaches a point at which the fan shuts down to a low speed. If I turn the temp control button to cooling and then reverse it to heating, the heat comes through warm and cozy for several minutes and gradually feeds in cool air. Turning the temp control switch further in the red zone does not help. On warmer days the system works just fine.

Any ideas concerning what I should be looking for. I thought about the thermostat but the car seems to maintain the proper engine temperature. And being able to get some short term results by turning the switch from cool to heat make me believe the thermostat is not the problem.

Any Suggestions!!!

Richclay