Lockout relays in air conditioning systems primarily prevent which condition?

• A. Prevent compressor short-cycling
• B. Lock out the overloads
• C. Lock out the thermostat
• D. Provide automatic restart

Answer: (A)

Preventing compressor short-cycling is what lockout relays aim to do. After a fault or shutdown, the relay imposes a minimum off time before the compressor can restart, so the system pressure and pressures in the refrigerant circuit have a chance to stabilize and the compressor can re-lubricate properly. This delay avoids rapid on/off cycling that would place high current demand on start, cause mechanical stress, wear seals and bearings, and shorten the compressor’s life. Because of that protective restart delay, lockout relays are not primarily about locking out overloads, locking out the thermostat, or providing automatic restart. They exist to ensure the compressor doesn’t restart too soon, i.e., to prevent short-cycling.