Moisture in the System
If moisture enters the air conditioning system, it will freeze at the system's metering device. It freezes at the expansion valve's port, where refrigerant is metered into the evaporator core. (TXV) Expansion valve air conditioning systems use a receiver drier that cleans and absorbs moisture from the refrigerant. If the drier becomes saturated with moisture, it will release it at the hottest times of the day. It only takes a few minutes for this moisture to freeze and deprive the evaporator core of refrigerant. This is why the customer was able to drive the vehicle for five or ten minutes before the valve froze and A/C performance was reduced.