AC Compressor (C) D Friedman Air Conditioner / Heat Pump Short Cycling
How to Diagnose an A/C or Heat Pump cycling on & off too rapidly

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Short on-off cycling of air conditioner or heat pump compressor/condenser unit diagnosis: what causes the A/C or heat pump fan condenser unit to keep cycling on and off rapidly and how do we fix it? Here we explain the common causes of compressor unit short cycling.

This article series explains how to diagnose an air conditioner or heat pump that is not cooling: this article explains how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity, reduced or no cool air flow, reduced or no actual lowering of the air temperature, or an air conditioner that won't start.

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Air Conditioner or Heat Pump Short Cycling Diagnosis

AC Compressor (C) D FriedmanReader Question: My Air Conditioner (or heat pump) keeps cycling on and off too rapidly - what might be wrong? short A/C on-cycle problems

Joe said: short cycling air conditioner compressor diagnosis: I have the same problem as Mathew: my A/C compressor cycles on and of every ~10 seconds. I is about 5yr old. What can we do to fix this system. Please help. Thanks!

Matthew said: short cycling air conditioner problems: Our air conditioning compressor cycles on and of every few seconds or minutes. What can we do to fix this systems not even a year old



Five causes of a home air conditioner compressor short cycling on and off too rapidly - Short Cycling Air Conditioner Diagnosis & Repair

DanJoeFriedman (mod) said to Joe and Matthew (re questions just above):

  1. Loss of air conditioner refrigerant - a refrigerant leak in the system. You may be able to repair the short cycling problem temporarily by recharging the air conditioning system but the proper repair is to find and fix the leak. Otherwise you will have to keep repeating the costly service call to just add refrigerant. See REFRIGERANT LEAK DETECTION.
  2. A/C Coil Icing - the evaporator coil (cooling coil) is iced over (such as due to improper refrigerant charge or dirt or a reduced air flow due to a dirty filter) - take a look in the air handler to see if the coil is blocked by ice or dirt.See FROST BUILD-UP on AIR CONDITIONER COILS
  3. Oversized air conditioner - if the short cycling has always been a problem since the day the system was installed, there is a good chance that the unit is too big (too many BTUS) for the space being cooled. A more subtle version of this same problem is that you've done something like closing doors or adding a partition that had the effect of reducing the size of the space being cooled. Sometimes we can mitigate this problem by running the blower fan at a lower speed or by opening interior doors to increase the size of the space being cooled or even by moving the thermostat. See AIR CONDITIONER BTU CHART and OPERATING TEMPERATURES HVAC
  4. A/C control problem - it's less likely, but a damaged control board or switch could also be causing rapid equipment on-[off cycling.
  5. Compressor damage or compressor start-troubles: - I've seen these other causes of air conditioner short cycling: if someone manually turns the air conditioner thermostat up and down or on and off too frequently, a hard-starting compressor may find that it has been shut down with high internal head pressure inside the compressor. Normally that head pressure bleeds off over time, making it easier for the compressor to re-start (against low head pressure) the next time it turns on.

  6. Thermostat wiring or device defects: check for loose thermostat wires, debris-clogging of a thermostat's bimetallic spring or thermocouple (and clean them)

  7. Bad thermocouple or dirty thermistor on gas fired equipment: Short cycling or unexplained on-off cycling of heating equipment has also been traced (by one reader) to a dirty or failing thermocouple (possibly the reader meant a dirty thermistor).
    This condition was reported in the FAQs by a reader commenting at HEAT ANTICIPATOR Adjustment

But if someone is turning the system on and off quickly, the compressor may have a hard time re-starting against the pressure on its outlet side. A starter capacitor addition or replacement might fix the problem. If your A/C compressor is showing this symptom but works OK if you leave it shut off for 30 minutes or longer, that may be the trouble.

We have also see or a damaged compressor internal refrigerant valve causing high head pressures;

In sum, you need a service call from a professional to correctly diagnose and repair the problem. Ask the service tech what she/he found and let us know - what you find will help other readers.

What about a compressor that stays on too long instead of too short a time?

If your air conditioner or heat pump has the opposite problem, staying on too long, see LONG-ON CYCLING AC COMPRESSOR.



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