A heating, ventilating, air conditioning or refrigeration system comprising: a condenser configured to condense refrigerant into a refrigerant liquid; a flash tank configured to receive the refrigerant as the refrigerant liquid from the condenser and to at least partially vaporize the refrigerant into refrigerant vapor; an evaporator configured to receive the refrigerant from the flash tank and to further vaporize the refrigerant into the refrigerant vapor; a compressor configured to receive the refrigerant vapor from the evaporator and to compress the refrigerant vapor for return to the condenser; an electronically controlled flash tank feed valve disposed between the condenser and the flash tank, configured to control a flow of the refrigerant liquid from the condenser to the flash tank; sensors (54, 56) configured to sense pressure and temperature of the refrigerant liquid as the refrigerant liquid flows from the condenser; characterized by a control system coupled to the flash tank feed valve and configured to regulate opening and closing of the flash tank feed valve to control the flow of the refrigerant liquid based upon an amount of subcooling of the refrigerant liquid, the control system being coupled to the sensors (54, 56) and configured to receive signals from the sensors (54, 56) representative of pressure and temperature and to calculate the subcooling of the refrigerant liquid based upon the signals for control of the flash tank feed valve, wherein the control system is coupled to the compressor and is configured to detect a feed forward parameter of the compressor indicative of compressor capacity, and wherein the control system is configured to regulate opening and closing of the flash tank feed valve based upon the feed forward parameter, such that the control system anticipates changes in the subcooling of the refrigerant liquid. a condenser configured to condense refrigerant into a refrigerant liquid; a flash tank configured to receive the refrigerant as the refrigerant liquid from the condenser and to at least partially vaporize the refrigerant into refrigerant vapor; an evaporator configured to receive the refrigerant from the flash tank and to further vaporize the refrigerant into the refrigerant vapor; a compressor configured to receive the refrigerant vapor from the evaporator and to compress the refrigerant vapor for return to the condenser; an electronically controlled flash tank feed valve disposed between the condenser and the flash tank, configured to control a flow of the refrigerant liquid from the condenser to the flash tank; sensors (54, 56) configured to sense pressure and temperature of the refrigerant liquid as the refrigerant liquid flows from the condenser; characterized by a control system coupled to the flash tank feed valve and configured to regulate opening and closing of the flash tank feed valve to control the flow of the refrigerant liquid based upon an amount of subcooling of the refrigerant liquid, the control system being coupled to the sensors (54, 56) and configured to receive signals from the sensors (54, 56) representative of pressure and temperature and to calculate the subcooling of the refrigerant liquid based upon the signals for control of the flash tank feed valve, wherein the control system is coupled to the compressor and is configured to detect a feed forward parameter of the compressor indicative of compressor capacity, and wherein the control system is configured to regulate opening and closing of the flash tank feed valve based upon the feed forward parameter, such that the control system anticipates changes in the subcooling of the refrigerant liquid.