Originally Posted by upallnight

An evaporator that is freezing up means the charge is low. Low side pressure should be around 35 psi to 45 psi depending on the ambient temp. Unlike refrigerator where you want the evaporator temp to be below freezing, automotive AC is designed so that the evaporator never get to the temp that will allow it to freeze up. Frost free refrigerator has a heating coil that is set on a timer to melt the ice that forms on the condenser. Automotive AC does not have this.