My 2001 gmc sonoma's heater started acting up today. It would only blow hot air while while accelerating with high rpm. Then when I would level my speed off cold air would blow again. Anyone know what the problem could be?
you should check your coolant level. sounds like you have a low coolant level. you will have air in the heater core until you rev up the engine and the water pump pushes more coolant. then when the engine rpm goes down the coolant flow goes down.