Pontiac Repair: 2002 Pontiac bonneville, pontiac bonneville, temp gauge

Question
What would cause the heater to only blow cold air? Occasionally it will blow warm air but mainly cold air. When it is switched from ac to the heater the heater blows cold air and the air flow is not a strong.

Answer
Hi Lisa:

well First off if the car is equipped with a temp gauge does the guage show the engine at normal engine tempature when it's hot? if not then it's possable it has a bad thermostat in the engine or the engine is low on coolant. If the engine is low on coolant a likley cause is a leaking upper inatke manifold plenium gashet or a bad manifold leaking coolant out the rear of the engine. If the coolant levle is okay and the engine appears to be in the normal temp range the last mechanical issue could be a plugged heater core which owuld need to be back flushed out. Then there is the possability of a temp door issue in the car. you said from heat to A/c the fan noise changed that could be due to the are inlet door operation. leave the hvac control on vent and then sweep the temp frm hot to cold and note any change of air delivery or sound. if it changes the door is moving which is good. if not then ther could be an issue with the temp door motor on the HVAC box. good luck :)