Forum Discussion

Tweege's avatar
Tweege
Explorer
Jul 16, 2017

AC cycling on off rapidly

Seems like my ac started acting up after it reached the thermostat set temp. Sounded like the compressor was cycling on and off( could hear clicking from the overhead unit) sometimes very rapidly and sometimes after a few seconds. Either way the fan never stopped while it did this. If I moved the temp down it would run normal for a while, then would start clicking on off again. After it finally tripped the breaker, I just shut it off.

Any ideas on the culprit or troubleshooting ideas. I'm leaning towards the thermostat given the way it is acting.

Thanks, Tim.
  • I'm thinking it's trying to come back on too quickly and tripping its own overlaod breaker. When that happens you hear a hum like the compressor is starting and then a click as the breaker cuts it back off. Then the question is why is it doing that?
    You could also have a blown or failing start capacitor. Heat and low voltage maybe be driving it to fail. Or the compressor itself may be going but that isn't likely.
    If you haven't ever replace these, it shold be done every ten years or more if it's used a lot.
    I would check the start cap(s) first. They're a cheap and easy fix.

    Your thermostat should not allow the compressor to come back on within 5 minutes of it shutting down. This protects it from dead-heading.
  • What thermostat exactly? Could it be switching the fan between high and low speed?
  • wnjj's avatar
    wnjj
    Explorer II
    I'm going with the thermostat as the cause too. Something is making tell the compressor to start when it shouldn't. Is your house battery good? If the battery is bad and pulling the converter down (assuming the converter is on and working), low voltage at the t-stat could make it act up.

    If all else checks out, it's likely a failed t-stat.
  • Not the fan switching speeds. Fan continues to run at same speed when the clicking occurs. Can hear the hum of what I assume is the compressor going on and off.

    Battery is still good also.

    Thanks for the suggestions
  • If it's a Dometic it's normal for the compressor to stay running when the fan switches from high to low. The fan turns off completely for a second or two then comes back on. If the compressor is kicking on and off something is wrong.
  • Need to measure voltage in the RV when this is happening. Good chance low voltage is the issue.
    If voltage is good you need an amp reading for the A/C circuit and compare to model specifications as it most likely is tripping the internal self resetting thermal breaker.
  • ScottG wrote:
    I'm thinking it's trying to come back on too quickly and tripping its own overlaod breaker. When that happens you hear a hum like the compressor is starting and then a click as the breaker cuts it back off. Then the question is why is it doing that?
    You could also have a blown or failing start capacitor. Heat and low voltage maybe be driving it to fail. Or the compressor itself may be going but that isn't likely.
    If you haven't ever replace these, it shold be done every ten years or more if it's used a lot.
    I would check the start cap(s) first. They're a cheap and easy fix.

    Your thermostat should not allow the compressor to come back on within 5 minutes of it shutting down. This protects it from dead-heading.


    X2 on the starting capacitor.

    Good luck,
    Stu
  • Community Alumni's avatar
    Community Alumni
    Mine has done that on occasion when I have the thermostat set a little too high, i.e. 73F. It seems to reset itself if I drop it down to 68-70F. The compressor kicks in normally and it runs without issue.

    I have to keep my wife from playing with the temperature setting! :B