Short cycling is when an HVAC system turns on, runs for a brief period (typically less than 5 minutes), shuts off, then restarts a few minutes later. Healthy HVAC cycles last 10-15+ minutes. Short cycling wears equipment fast and indicates a problem.
Common causes
- Dirty filter — restricts airflow, heat builds up too fast, triggers high-limit switch
- Oversized equipment — common when furnaces or ACs were sized by rule-of-thumb instead of Manual J
- Failing flame sensor (furnaces) — system can’t confirm flame, shuts down repeatedly
- Closed supply vents — same effect as dirty filter
- Thermostat location or wiring issue — reading wrong temperature
- Low refrigerant (ACs) — causes coil to freeze, system shuts down
Why It’s Expensive
Equipment is most efficient at steady-state. Each ignition cycle wears the igniter, blower, and inducer. A short-cycling system loses 10-15% of useful life every season it’s allowed to keep doing it.
First step: replace the filter, open every vent, check the thermostat for drafts/sun exposure. If that doesn’t fix it, schedule a diagnostic — usually a quick fix.
Related: Manual J, Flame Sensor, Static Pressure.
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Right Way Mechanical is a family-owned HVAC contractor serving Wheat Ridge, Arvada, west Denver, and the Colorado foothills.