A/C Unit Cycles On and Off: What Is Wrong?


An A/C unit that cycles on and off rapidly can create a number of problems. The rapid cycling generally causes improper cooling in the home, increased wear to the A/C unit and will also spike an increase in energy consumption. It is important for a homeowner to quickly determine why the unit is rapidly cycling before the problem worsens.

Normal Cycling

  • Modern A/C units may cycle on and off more quickly than older units as a way of saving energy. If a homeowner has a newer unit, he should check its owner's manual for information on the proper operation of the unit. If the manual is missing, he should contact the manufacturer for this information. On older A/C units, one that is cycling more quickly than in the past generally indicates a problem. A/C units will also cycle off and on more quickly on very hot days.

Proper Use

  • An improperly adjusted thermostat may cause the A/C unit to cycle on and off. Check the thermostat that controls the air conditioner to make certain it is set up correctly. The air conditioner owner's manual should cover proper thermostat setup, or the thermostat may have a separate owner's manual. A home with significant drafts that allow hot air to enter the interior may cause the unit to rapidly cycle. The A/C unit should be properly sized for the home or area of the home that the A/C unit will cool. A unit that is too small will not be able to cool the home efficiently, causing it to run more frequently. A unit that is too large will cool the home too quickly, causing it to cycle on and off frequently and preventing the unit from properly dehumidifying the air in the home.


  • An improperly maintained A/C unit will not operate at peak efficiency. This may cause the unit to cycle off and on more quickly to make up for this inefficiency. The homeowner should make sure that the unit's filter is clean and that nothing is blocking the air return duct inside the home. The homeowner should also inspect the exterior of the A/C unit for any leaves and other debris that have built up around the unit as this can restrict air flow, causing the A/C unit to operate at a higher temperature than needed.


  • As an A/C unit ages, the unit can lose refrigerant, and parts on the unit can begin to fail. A low coolant level is a common cause of A/C unit cycling in older units. Though in some cases a homeowner can charge his own A/C unit, having the work completed by a certified technician is a better option in most cases. The technician will be able to check for other problems and assure that the refrigerant does not escape into the environment. Other internal components in the unit may fail and cause an A/C unit to rapidly cycle. Generally, a repair technician can quickly isolate and repair the problem.

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