DEFROST CONTROL FOR SPACE COOLING SYSTEM

摘要

An improved defrost controller (20) is provided for a space cooling system (10) of the type having an evaporator (12) in heat exchange relationship with a space to be cooled, a condenser (14), a compressor (16) for circulating heat transfer fluid between the evaporator (12) and condenser (14), an expansion valve (18) located between an outlet (17) from the condenser (14) and an inlet (19) to the evaporator (12), and a defroster (36) operatively associated with the evaporator (12). The expansion valve (18) is positionable in a plurality of positions to maintain a desired level of superheat across the evaporator (12). The defrost controller (20) monitors the expansion valve position and activates the defroster (36) in response to the expansion valve (18) being in a more closed position than a predetermined defrost target position. The defrost controller (20) is further operable to prevent defrosting from occurring at times other than predetermined allowed defrost times, even if the position of the expansion valve (18) indicates a demand for defrost.