The reasons are as follows:
1. The vehicle's heater switch is faulty;
2. The air conditioning filter is too dirty and the air cannot be discharged;
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3. The heater failed; 4. The engine thermostat was damaged;
5. There was a lack of antifreeze;
6. It’s time to replace the antifreeze It needs to be replaced periodically;
7. The antifreeze circulation line of the vehicle is blocked.