Abstract: A computer cooling system has gaseous refrigerant compressed in a compressor and delivered to a first stage condenser. The first stage condenser includes a heat exchanger through which return coolant from the building heating system circulates to partially condense the gaseous refrigerant. The partially condensed refrigerant is directed to a second stage condenser wherein a portion of the refrigerant is diverted and flashed through an expansion valve into the second stage condenser to fully condense the nondiverted portion of the refrigerant before delivering it to the cooling coils of the computer. A pressure regulator valve controls the pressure and temperature of the diverted refrigerant in the second stage condenser to ensure that the nondiverted refrigerant is fully condensed. The used diverted refrigerant is discharged from the second stage condenser through the pressure regulator valve into an accumulator which also collects return coolant from the cooling coils of the computer.