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Compressors are used in all kinds of restaurant equipment from refrigerators and freezers to walk-ins, from merchandisers and display cabinets to condiment and frozen beverage dispensers and much more. A compressor is a mechanical device (a motor) that increases the pressure of a gas by reducing its volume to affect cooling via the transfer of heat.

Compressors used in refrigeration systems are often described as being either "hermetic" or "semi-hermetic". The difference between the hermetic and semi-hermetic types is their design and construction. A hermetic compressor has a one-piece welded steel casing that cannot be opened for repair -- if the hermetic unit fails, it is simply replaced with an entirely new one. A semi-hermetic compressor uses a large cast metal shell with gasketed covers and screws that can be opened in order to replace the motor and other internal components.

Relays are electrical devices that are used to control circuits in restaurant equipment and other types of machinery. They work by using a small electrical current to control a larger current, allowing a low-power control circuit to switch a high-power circuit on or off.

In restaurant equipment, relays can be used to control a variety of functions, such as turning on and off motors, controlling heating elements, and activating alarms. For example, a relay might be used to turn on a refrigerator's compressor when the temperature inside the fridge reaches a certain level, or to turn off a stove's heating element when the temperature reaches a certain point. Relays are often used in restaurant equipment because they can handle large amounts of current and are able to switch circuits on and off quickly and reliably.

Start components (start capacitor) are used to assist the compressor (or motor) on startup. This is added to the circuit along with a potential relay. The potential relay is necessary because to isolate the start capacitor from the compressor circuit after the compressor starts. The potential relay allows the start capacitor to assist the compressor to start. It then opens the circuit between the compressor and the start capacitor after the compressor starts and is running. The potential relay does this using back EMF or back electromotive force, otherwise known as "back voltage" coming from the compressor. As the compressor starts and voltage goes through the system, it sends out a back EMF voltage. Furthermore, this voltage energizes the coil in the potential relay for the start capacitor. The back EMF is constant while the compressor is running. The potential relay will hold the start capacitor out of the compressor circuit because of the Back EMF until the compressor stops. Then the coil in the relay is de-energized and the start capacitor awaits another startup.