Santana 2000 has no warm air. What caused it? Friends, please do me a favor.

If it is not hot enough, the reasons are 1: the water inlet valve is blocked; 2: The heater water tank is blocked; 3. Thermostat failure (causing the engine water circulation system to enter the open-loop state prematurely and be replaced); 4: The water tank and waterway are blocked by air (just exhausted); 5. Pump failure is generally due to the local water temperature is too high and the local water temperature is too low, resulting in water not circulating; If it is not hot at all, you can't circulate.