Why does the heater blow hot and cold intermittently?
1 Answers
There are two main reasons why a vehicle's heater may alternate between hot and cold air: 1. Hot water occasionally fails to enter the heater core: (1) Malfunction of the heater control valve. (2) Air in the coolant system. (3) Insufficient antifreeze. (4) In some vehicles, the heater control valve is controlled by the air conditioning computer. During operation, internal sticking or influence from the air conditioning computer may cause the heater control valve to close or fail to open. 2. Hot air is not delivered through the vents: (1) Sticking of the air conditioning heater blend door or malfunction of the control motor. (2) If the blend door motor responsible for regulating hot and cold air malfunctions, it can also cause temperature fluctuations in the heater output.