(A) room thermostat (B) liquid line solenoid valve (C) low pressure control
(D) de-energized 3-Way valve (E) opened check valve (F) TXV (Thermostatic expansion valve)
(G) closed checkvalve (H) crankcase pressure regulator (I) a timeclock (J) drain pan heater
(K) hot gas solenoid valve (L) 3-way valve pressure control
(M) defrost termination pressure control (N) Fan delay control.
The clock de-energizes (closes) the liquid line solenoid valve which causes the compressor to pumpdown and shut off from the low pressure control. The clock also energizes the (J) drain pan heater in the evaporator and timer relay which after a two minute delay energizes (opens) the 3-way valve and (K) hot gas solenoid valve which then builds up pressure in the evaporator causing the low pressure control to close and start the compressor.
The hot discharge gas from the compressor flows through the 3-way valve, Hot gas valve and check valve forcing all the liquid left in the liquid line into the evaporator. If pressure builds up too high the (L) 3-way valve pressure control will de-energize the solenoid valve and allow pressure to relieve through the condenser. Pressures within the evaporator will remain steady and once all the frost has melted the pressure will rise until the (M) defrost termination pressure control energizes the timeclock’s internal solenoid terminating the defrost cycle. The 3-way valve, hot gas valve solenoids are then de-energized. The liquid line solenoid valve opens and the compressor continues to run. The evaporator fans do not start up until the pressure in the evaporator is low enough to close the (N) Fan delay control. By delaying the fans this allows any moisture left on the coil to drain away or freeze. As soon as the evaporator fans are energized the system will then resume back to the refrigeration cycle.
The liquid then flows to the receiver through the (E) opened check valve and on through the coiled liquid line within the suction accumulator (this performs the function as a suction to liquid heat-exchanger). The sub-cooled liquid then flows through the liquid line solenoid valve (energized/open) and on to the (F) TXV (Thermostatic expansion valve).
The refrigerant is then directed through the distributor at a lower pressure and flows into the evaporator. Refrigerant is prevented to flow past the (G) closed checkvalve.
The refrigerant liquid / vapor mixture is then boiled by the warmer box air from the evaporator fan. The refrigerant vapor then flows though a (H) crankcase pressure regulator preventing a motor overload from high suction pressures and enters the two suction accumulators and on to the compressor.