Abstract: The present invention relates to heat pumps which include a freeze-up prevention device for use during the heating cycle. The heat pump consists of the normal compressor which connects by means of a four-way valve to an inside coil and an outside coil. An expansion valve and appropriate check valve allow the flow of refrigerant between the inside and outside coils. During the heating cycle, the inside coil is the condenser and the outside is the evaporator. The freeze-up prevention device is a small insertable unit immediately prior to the evaporator which allows the refrigerant to flow therethrough. The insertable unit has a heating element operable by a thermostat attached to the outside coils with the thermostat closing a switch to allow current to flow to the heating element when an icing condition is sensed. The insertable unit, via the heating element, transmits heat directly to the refrigerant thereby preventing freeze-up of the evaporator coil.