I've had this problem with the flapper in the dash that directs the air through the heater core initially blowing warm air then randomly switching itself to cold. If you rotate the hot cold **** from hot to cold and back to hot it will usually move the flapper back so the air gets hot but if you touch the **** at all it goes cold again immediately. I've reviewed the old threads and am confused exactly which part I need to buy. Is it the dash control unit which includes the ***** etc. I'm attempting to attach a picture of the dash control unit. If I buy this does that fix this problem?

 

It could be one of two things. The controls themselves or the amplifier. I had the same problem and it was the controls that were faulty. I swapped them with a new unit and it has been fine ever since.

 

Thanks for the info, did you end up replacing the part in the picture?