Why the AC start to blow white vapor through vent in VW Passat?

White vapor coming out of the air conditioning vents in a VW Passat is typically caused by a refrigerant leak in the system. Refrigerant is a chemical that is used to cool the air inside the car, and when there is a leak, the refrigerant can escape and cause the AC to malfunction.

Here are some of the symptoms that may indicate a refrigerant leak:

* The AC is not cooling the air as well as it used to.

* The AC is blowing out warm or humid air.

* There is a hissing or bubbling sound coming from the AC unit.

* The AC compressor is cycling on and off rapidly.

* There is a white or gray residue around the AC vents.

If you are experiencing any of these symptoms, it is important to have your AC system inspected by a qualified mechanic as soon as possible. A refrigerant leak can cause further damage to the AC system and can also be harmful to your health.

Here are some of the things that can cause a refrigerant leak:

* A damaged AC compressor.

* A damaged condenser.

* A damaged evaporator.

* A damaged refrigerant line.

* A faulty expansion valve.

A qualified mechanic will be able to diagnose the source of the leak and repair the AC system.