The reasons are as follows
First, check whether the engine's operating temperature is normal. If the engine's operating temperature is low, the thermostat is not closed tightly, and you can consider replacing the thermostat. If the engine operating temperature is normal and the heater water pipes in the cabin are hot and cold, it means that the heater water tank is clogged. It is recommended to clean it. You can consider removing the heater inlet and outlet pipes and blowing them with a water gun or air pump. clear. If there is no problem with the warm air pipe, then the servo motor of the hot and cold air plates inside the air conditioner air box is not in place or the air plate is stuck. Check it and adjust it in place and it will be fine.