This switch is used on semi-hermetic compressors to protect them in the event there is an oil pressure problem causing the lack of lubrication of the reciprocal compressor. The operation of this control is relatively simple, yet many technicians become confused when working with the control. The opfc is a pressure actuated control, using two opposing pressure diaphragms. The capillary tube of one diaphragm is connected to the oil pump port. It senses the actual oil pressure being produced by the pump. The other capillary tube from the other diaphragm is connected to the low side (suction) of the system. For example, the oil pump has an output pressure of 30 psi. It is an R-22 system with a 65-pound back pressure. A spring will apply pressure on the oil pump diaphragm of the control. The spring is adjusted to a 35-psi pressure causing equal pressure also have a wet rag or other type of heat sink to absorb excessive heat as not to warp the valve body causing inconsistent of possibly no operation.
Another important factor about solenoid valves that I want to point out to you at this time is the possibility of installing a solenoid with a manual opening device. In cases where a solenoid is being used for a liquid line pump-down valve, a solenoid with a manual opening valve should be used. In the case of a commercial air conditioning or refrigeration system, when the holding coil fails or a problem develops in the control circuit, the valve can be opened manually. This will manually open the valve and allow the unit to operate while you either secure another coil or diagnose and correct the problem.
This type of valve can be used for many applications. It is used to defrost evaporators with the use of hot gas, it is used for pumping down a unit causing it to shut down with the low-pressure control switch, it can be used for water turn off. The list goes on and on. If you are designing something that requires an electrically-operated valve, check out the specifications of the solenoid valve.