Short cycling is when a furnace, air conditioner or heat pump turns on and off in rapid cycles, running only a few minutes before shutting down without completing a normal heating or cooling cycle. Common causes include an oversized system, a clogged air filter, low refrigerant, a furnace overheating and tripping its limit switch, or a poorly placed thermostat.
Why it matters to you
Each start is the hardest moment for a compressor or ignition system, so frequent short cycles add wear, waste energy and leave rooms uneven or humid.
Practical guidance
Replace the air filter first and make sure supply and return vents are open and unblocked. If cycling continues, have the system checked, since a furnace that repeatedly trips its high-limit switch is stressing its heat exchanger.