if any flow of ambient air downwardly into the coil application_number US 68130991 A description referring now to fig1 there is shown a heat pump system 11 of the type with which the present invention is employed it includes an outdoor coil 12 and a compressor 13 forming part of the refrigeration circuit along with the indoor coil and refrigerant expansion device not shown as are found in a conventional system also in a conventional manner a four way valve 14 provides the flexibility of the heat pump to be operated in either the heating or cooling mode by directing the refrigerant to the indoor or outdoor coils respectively this valve also allows the system to operate in the defrost mode to direct the hot discharge gas to the outdoor coil also forming part of the refrigeration circuit is the liquid distributor 16 and the vapor header 17 when operating in the heating mode the liquid distributor 16 distributes the liquid refrigerant to the individual circuits of the outdoor coil 12 after it has passed through the expansion device and the vapor header 17 is a common point at which all of the refrigerant passing through the outdoor coil is combined and passes to the reversing valve 14 in the cooling and defrost modes of operation the liquid distributor 16 is the common point at which all of the refrigerant passing through the outdoor coil 12 is combined and.