HVAC Evaporator Cooling cycle
During the normal cooling cycle controlled by a thermostat, as room temperature rises above the high setting on the thermostat there is a need for refrigeration. Liquid solenoid (valve A) and the built-in pilot (valve D) open, allowing refrigerant to flow. The opening of the built in pilot allows the pressure to bypass the sensing chamber of valve D. This forces it to remain wide open with resultant minimum pressure drop through the valve.
When the room temperature drops to the low setting on the thermostat, there is no longer need for referation. Solenoid valve A and pilot valve D close. They remain closed until refrigeration is again required. Hot-gas valve C and defrost water solenoid valve E remain closed during the cooling cycle.