When your car's AC is blowing mist, it's a sign that the system is overworked and needs to be serviced. The mist is actually condensation from the evaporator, and it's a sign that the evaporator is not able to effectively remove heat from the air. This can be caused by a number of things, including a dirty evaporator, low refrigerant levels, or a problem with the compressor. If your AC is blowing mist, take it to a mechanic to have it checked out and serviced.