The thermostat is often turned on or turned on too early, which makes the cooling system carry out a large cycle too early, and the outside temperature is very low. Especially when the car is driving, the cold air quickly cools the antifreeze, the engine water temperature does not rise, and the warm air does not heat up.
2.
The impeller of the water pump is damaged or lost, so that the flow through the warm air small water tank is not enough and the heat cannot come up.
3.
There is air resistance in the engine cooling system, which leads to poor circulation of the cooling system, high water temperature and not hot warm air.
I hope it helps you. I hope it can be adopted. Thank you!