Bottom hot-gas feed
The multiple system shown in Fig. 10-20 shows a check valve mounted in each of the liquid-refrigerant branch lines. A single solenoid valve is used in the main refrigerant line. The defrost gas is bottom fed.
The system illustrated in Fig. 10-21 shows a check valve mounted directly at the outlet of each of the liquid-solenoid valves. The defrost gas is top fed. This system permits selective defrosting of each evaporator. A single accumulator is used to protect the compressor during defrost, as well as to accumulate both liquid refrigerant and defrost condensate. This protection is accomplished by using a differential pressure–regulator valve in an evaporator bypass circuit.
The differential pressure–regulator valve will open sufficiently to relieve excess pressure across the compressor inlet. The pressure will discharge as excess pressure differential occurs. When the pressure differential is less than the regulator-valve setting, the regulator will be tightly closed.