Relays in air conditioning units work by applying electric currents to contacts within the appliance. When a relay contact is normally open, there is an open contact when the relay is not energized, but when a relay contact is normally closed, there is a closed contact when the relay is not energized. In either case, applying electrical current to the contacts changes their state, causing the relay to work.
Relays involve two circuits that acquire energy for the air conditioner to function, namely the energizing circuit and the contact circuit. The coil is on the energizing side, while the relay's contacts are on the contact side, which allows room for the current to travel. When a relay's coil is energized, current flow through the coil creates a magnetic field that powers the system. One end of the armature is attached to the metal frame, which is formed so that the armature can pivot, while the other end opens and closes the contacts, allowing energy to be used by the device.
Relays switch smaller currents in a control circuit to power a current and do not usually control power-consuming devices except for small devices that draw low amps. However, relays can take control of larger voltages and amperes by having an amplifying effect; a small voltage applied to a relay's coil can result in a large voltage being switched by the contacts.