Fix it

Why is my AC short cycling?

Cooling in bursts of a few minutes is hard on the compressor — the most expensive part in the system — and it rarely gets the house comfortable. The causes range from a thermostat placed badly to a system protecting itself.

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What it usually is

  1. An iced or airflow-starved coil tripping protection

    Low airflow ices the coil; pressure drops and safeties cut the compressor, which restarts after a rest and repeats. A dirty filter is the usual first domino.

  2. Refrigerant loss dropping pressure below cutoffs

    The low-pressure switch cycles the compressor to protect it. Cooling is weak throughout, and the cycling worsens on hot days.

  3. A thermostat in a draft or sun patch

    A thermostat that a supply vent blows across, or afternoon sun hits, satisfies and un-satisfies in minutes. The house never agrees with the wall.

  4. An oversized system built to sprint

    Too much capacity cools the thermostat before the humidity leaves the air — short, cold, clammy cycles since installation rather than a new fault.

What you can check yourself

New filter, open registers, and check the indoor coil area for ice — if iced, run FAN only for a few hours to thaw before any diagnosis. Note what the thermostat experiences: vent draft, sunlight, lamp heat. Time the cycles for the service call.

When it’s a job for a pro

Pressure-switch cycling and charge problems need gauges; chronic oversizing conversations are worth having at replacement time, not before. A technician can also add a short-cycle delay if the control lacks one.

Thaw-and-correct airflow visits typically run $150 to $350; charge diagnosis $200 to $500. Compressors lost to years of short cycling run $1,200 and up — the argument for solving it now.

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