My outside compressor / condenser is cycling on and off, even though the thermostat is calling for A/C.

The blower in the house still runs, and the thermostat is working properly. (I opened up the unit to see if the thermostat solenoid is working and it checks out okay)

The filters have recently been replaced and I cleaned the condenser coils in early spring.

It appears to be overheating causing it to cycle off, then when it cools down it goes back on.

Could it be the run capacitor?

  • It could be the capacitor. Do you notice the lights dimming in the house when it is running? It could also be low on freon. do you notice any Icing on the evaporator (coil in side the furnace) this could also provide a clue.
    – Ed Beal
    Jun 1, 2016 at 19:37
  • Check the freon is my first vote, capacitor would be next in line.
    – Tyson
    Jun 1, 2016 at 20:00
  • What's the make and model of the unit? Does the whole condensing unit shut down, or just the fan or compressor? What's the ambient outdoor temperature, and what at what temperature is the thermostat set for?
    – Tester101
    Jun 2, 2016 at 14:05
  • 2
    Any chance your power company has a load management device installed? In our area, the PoCo offers a $ incentive to let them switch off your compressor for a few minutes at a time if they are short on capacity.
    – TomG
    Sep 1, 2016 at 14:24
  • 1
    Do you have a smart thermostat? I had a similar issue a few months after I installed a Nest. Turns out the Nest charges itself by sipping off the AC (or heat) connection. Mine wasn’t providing enough power, so it began this cycling that revved the AC unit repeatedly. Installing a common wire solved it. Nov 13, 2017 at 3:56

3 Answers 3


Could well be it is overheating and shutting down. Have you had the Freon checked lately? You can put a food thermometer in an vent opening; if the temperature at the vent is over 65 degrees Fahrenheit it is probably low on Freon, and the A/C unit is trying to run 100% of the time to try to cool down.

This happened to me, and the repairman said that was the cause for my situation. Worked like a charm after the recharge.

  • 2
    Side note: If it's low on refrigerant, then just 'topping it up' is not an acceptable solution; it's got a leak. Find it and fix it. Sep 11, 2017 at 17:41
  • 1
    Depending on the age of the unit a leak may never be found, I recently serviced a old r22 unit that had never been serviced in over 20 years it took 3 lbs of Freon to get super heat & sub cooling temps in spec and there were no leaks I could detect and I have top of the line detectors.
    – Ed Beal
    Jun 13, 2018 at 15:33

Considering it's cycling on and off I wouldn't think it's the freon. I would look at the high pressure cut-off first. You might be building too much pressure and causing it to shut down.


With out the make and model the best that can be done is guess. Both high side (probably mandated in your area) and low side cutouts can cause this as well as an oil switch. You probably have the high side but the other two would be optional. Try to measure the temperature of both the condenser and evaporator coils (expect about 45F give or take about 10F depending on ambient. Checking the appropriate refrigeration tables you can approximate what it should be once you know the temperature. Check to be sure the thermostat is not cutting out. If you have the skill set short the appropriate wires and see if that solves it. The problem will return when the short is removed and the problem found. Check anything that has changed in the system since it last worked.If you cannot find it it is best to get a professional, tapping into the refrigeration system or electrical system can be dangerous and may require a licence depending on area.

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