Climate control runs hot and cold

[Green Machine]

Hi folks - the climate control in my '80 300SD works well for the most part - plenty of heat, especially in Vancouver Island's relatively balmy winter weather. But every now and then (even when the in-car temp is still relatively cool), it blows a blast of frigid air for 1-3 minutes before once again kicking out the heat. Is this normal? If not, what's a likely reason for this?

Cheers.

[michael rybikowsky]

Your cc servo may be slow.You need to excercise it on a regular basis.First set the def on.This will run the servo to full heat.Leave it there for five min or so.Now make sure the temp wheel is on lowest setting,and press high auto leave this on for the same amount of time.Repeat a few time.This may correct it.There are other things but this may be worth a shot good luck Michael. Carpe Diem.

[Elripster]

I'm not sure if this is you problem, but I had an AC/heat flip flopping problem. If I turned on the AC, it would blow cold, then hot, and back and forth. When I put the heat on, it would work if I set it hot, but it would come on strong then shut off or cool the car if in median settings. The culprit was a bad thermistor. It was hard to trouble shoot because at the temperature it was most often when I'd test it, it would read fine. However, if it cooled just a enough, it would drop from like 1700ohms to 2 and that would tell the AC servo the car was way cold, crank up the heat. When it jumped up to the higher ohms, it would tell it its too hot cool it down. My car is a 79 and your's and 80, for the 40 bucks you might just replace it.

Frank.