According to your situation, I'm afraid the air conditioner heater didn't work normally, but just blew the heat from the engine to the cab. Because the air outside the car is very cold in winter, when the air conditioner is turned on, the cold air outside the car is inhaled and passes through the engine, naturally taking away the heat of the engine, and the temperature of the engine water tank drops. After all, the engine is not an electric furnace, and the heat is not enough to heat the cold air, so the warm air is not hot!