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Air conditioner turning on and off
A system that runs for a few minutes, stops and starts again never gets the house comfortable and wears itself out doing it.
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The short version
- Most likely cause
- A dirty filter, a thermostat in a bad spot or a system too large for the house.
- Safe to check
- The filter, the vents and where the thermostat sits.
- Call a technician when
- It still cycles every few minutes with a clean filter.
Safe to check yourself
- Replace a dirty filter.
- Open closed supply vents and clear blocked returns.
- Check that the thermostat is not in direct sun or above a vent.
- Time the cycles so you can describe them.
Stop and call
- Cycles are shorter than about ten minutes all day.
- The outdoor unit clicks on and off without cooling.
- There is ice on the lines.
- The breaker trips during a cycle.
What makes a system short cycle
- Restricted airflowToo little air makes the system overheat or freeze, and its safety controls shut it down.
- Thermostat placementA thermostat near a vent, a window or a lamp reads the wrong temperature and ends the cycle early.
- An oversized systemA unit too large for the house cools the air fast and stops before it has removed the humidity.
- Low refrigerantLow pressure trips a safety switch. The system restarts, trips again, and repeats.
What a technician will do
- Time the cycles and read the thermostat settings.
- Check the filter, coil and blower for airflow.
- Measure the refrigerant charge and the electrical parts.
- If the unit is oversized, explain the options honestly.
Frequent starts are the hardest thing an air conditioner does. Compressor and fan controls wear out faster in a system that cycles on and off often.
Related guides
Air conditioner running but not cooling
Ice on the air conditionerSources
- US Department of Energy