A residential compressor repeatedly shuts off on a safety control and immediately restarts within seconds, causing high inrush current each time. What component should a technician install to prevent this damaging short-cycling?
- AHard start capacitor
- BAnti-short-cycle timer (time-delay relay)
- CLow-pressure switch
- DCrankcase heater
Show answer & explanationAnswer & explanation
Correct answer: B. Anti-short-cycle timer (time-delay relay)
An anti-short-cycle timer (time-delay relay) prevents the compressor from restarting for a set period (typically 3–5 minutes) after shutdown, allowing system pressures to equalize and the motor windings to cool, thereby preventing damaging repeated inrush currents. The other components address different issues: crankcase heaters prevent refrigerant migration into the oil, low-pressure switches protect against low suction pressure, and hard start capacitors assist compressor startup torque.
Why the other options are wrong
- A. A hard start capacitor helps overcome starting torque but does nothing to delay restart timing.
- C. A low-pressure switch is a safety control, but it doesn't prevent rapid restart cycling on its own.
- D. Crankcase heaters prevent liquid refrigerant migration into the oil sump, not short cycling.
Anti-Short-Cycle Timer
A time-delay relay that prevents a compressor from restarting for several minutes after shutdown, protecting it from damaging inrush current and pressure imbalance.
- Typical delay: 3-5 minutes after any shutdown
- Prevents motor winding damage from rapid on/off cycling
- Distinct from crankcase heaters and hard start kits, which solve different problems
Memory trick: Short cycling? Slow it down with a Timer