Patent ID: 7249468

Claim:
In an air conditioning system having a compressor for compressing a low pressure gaseous refrigerant to form a high pressure vapor, a condenser to which the high pressure vapor is fed and in which the vapor is cooled and returned to a liquid state, and an evaporator to which the liquid refrigerant in the condenser is fed and in which the liquid refrigerant is transformed to a vapor and absorbs heat from the surroundings to cool the surrounding air, the improvement comprising: a receiver connected between the condenser and the evaporator, said receiver storing extra refrigerant received from the condenser for use at low ambient temperatures, said receiver including a shut off valve which isolates the high and low pressure elements of the system from each other; a low pressure switch and shut off valve assembly connected between the evaporator and the compressor, said low pressure switch of said assembly detecting when the system is running at too low pressure and in response to such a detection shutting off the system; a head pressure control connected between the condenser and the evaporator, said head pressure control maintaining a minimum pressure in the high pressure portion ot the system; and a constant pressure valve connected to the evaporator for maintaining a constant pressure to the evaporator.