Why does the Jetta partner produce hot air even if the air conditioner is not turned on?

In addition to an engine cooling water tank, there is also a heater water tank in the car.

When the air conditioner knob is turned to the hot air damper, the switch between the heater water tank and the coolant channel will be opened, and part of the coolant will circulate through the heater water tank to heat the water tank blades, and then the fan will be turned on. Then blow hot air into the car.

The cold air works by compressing the refrigerant through the compressor - giving the air conditioner and refrigerator at home a working principle.