For the last year or so the heater has been acting up on this car.The temperature/blower controls on this car are mounted on a small panel in the center of the dash. The center knob is temperature, with an "auto" (blue dot) position on the left side, and a red dot detent position on the right side. The right hand control knob directs from where the air will blow and also selects AC, heat or defrost, and the left hand knob controls fan speed.
There has never been a problem with the air conditioner if that matters. However I honestly don't know if we ever really tend to select a particular AC temperature or are just happy when it gets "cold".
For the last year or so the only way it was possible to get heat or hot defrost was to turn the temperature control, the middle control of the three all the way to the red indent position on the right. The heat or defrost would be on full and you could set blower speed and that was ok. After a few minutes it would get too hot. Then you would have to turn the temperature knob slightly to the left just off the detent to get it to stop blowing hot. It would then gradually cool off until you would have to turn the knob full clockwise once again to the detent to get it to start blowing hot again. There was no temperature "control" to speak of. The temperature was either hot or cold. The blower speed control always worked normally as does the other control which directs and selects AC and where the air will blow through, as well as selects defrost.
We use this car for short trips in the Winter and since the heater and defroster were both functional this has been no real problem. However last night we went for a ride. It was raining and in the forties and misty. No matter what we tried, the heat and the defroster blew cold until the last two miles of the trip home. Engine temperature according to the dashboard gauge looked to be normal. But Winters can get cold here in New Hampshire and this is only the beginning, and so even if it was once again the "either on or off" scenario we must have heat and defrost working again consistently to some extent.
I am an electronics technician and so I feel that I have a good shot at fixing this if I were to try, however the problem is I do not understand exactly what is happening in this temperature control arrangement. I don't mind if it were to work once again either on or off but we must get it working before the really cold weather sets in. Can someone please help me with a little "theory of operation" discussion here? Thanks for any replies. Lenny.