Hello! This is because the heater tank in your car is leaking. The heater water tank is the main source of heating for automobile air conditioning. Its water tank is connected with the engine water, so your heater water tank leaks, and the engine water must be less. You can check whether there is water shortage first. If the temperature is too low, replace the heater water tank.
I hope my answer can help you? Have a good car. Ask the car master. 4S shop professional technician, 10 minutes to solve.