My 88 Chev 3/4 ton heater controls most often don't perform as requested. The air flow direction is often irregular as when, say, blow down it remains on defrost or vent. After time (sometimes ten minutes) it smartens up and corrects the error. Also the temperature control has failures. If you should try to adjust the temp up or down a bar or two it will often go to the extreme hot or cold. Tried replacing the control circuit board from the wreckers...same. Is this a vacuum system? Maybe that's the prob.
Feb 26, 2010 at 8:27 PM