What is the reason why the car heater is warm at idle but not when driving?

1 Answers
MacVictoria
07/30/25 10:12am
The reasons why the car heater is warm at idle but not when driving are: 1. The thermostat is always open or opens too early, causing the engine coolant to enter the large circulation for cooling before the water temperature rises; 2. The electric cooling fan is constantly running; 3. The heater core or coolant passages are blocked, preventing the heated antifreeze from circulating into the heater core; 4. The heater control valve cannot open normally. The functions of the car air conditioning system are: 1. To achieve cooling effect through the continuous phase change cycle of refrigerant; 2. To remove dust, odors, smoke, and toxic gases from the air inside the car, making the cabin air fresher, and to humidify the cabin air to increase its relative humidity.
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