I have a Heil hvac model. N44336336GKE100, The system works ok when in cool mode but when in heat mode the outside fan runs for 30 sec then shuts off for 20 sec and continually repeats the cycle. I changed the defrost sensor which seem to work but the following morning it went back into the same cycle . I checked the capacitor and the reading was same as the specifications. Can you point me the way before I do anything foolish. thanks.

  • When out of your depth, bring in a professional (and in many parts of the world, a licensed professional is highly advisable for refrigeration systems.) – Ecnerwal Oct 23 '15 at 23:45
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    One of the first things to check with HVAC systems is the refrigerant level. If that gets low, compressors tend to shutoff as a safety feature since the refrigerant also contains the lubricant needed by the compressor. – BMitch Oct 24 '15 at 1:58

I imagine you are referring to Heil Model N4H336GKE100.

Check the test control jumper on the defrost control board. In the "speed up" test position it will cause the timing you describe. For normal operation the test jumper should be OPEN (no jumper or metal object shorting the test pins together). The default for the timing jumper is usually "60." For dry climates the timing jumper should be "90".

The tech support manual is posted at this address:


Here is a snapshot from the relevant section:

enter image description here

  • Thanks for your help but that doesn't seem to be the problem. The contactor doesn't engage long enough to jump the pins. I'm bewildered because the system works fine in the cool mode but when in the heat mode the contactor is tripped on and off continuously. – Erling Pacheco Oct 24 '15 at 22:47
  • "Contactor doesn't engage long enough to jump the pins"?? I do not know what you mean by this. I am not suggesting to put it into test mode. What I am suggesting is that it may presently be in test mode due to an unwanted short across the test pins. It also may be possible that your defrost board has failed such that it is always in test mode. The defrost/test cycle is only active during heating mode. It is not active during cooling mode and thus it is no surprise that cooling mode functions normally. – user39367 Oct 25 '15 at 1:29
  • Did change the board but the problem continues. I'll have to check the refrigerant. – Erling Pacheco Nov 3 '15 at 0:24
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    It sounds as though you have no options left that do not require some refrigerant expertise. If it is low enough on charge to starve the outdoor coil in heating mode, then the unit certainly would not cool well in cooling mode. That seems unlikely based on your original post. Someone who knows how to use a set of gauges and temperature probes should be able to identify the problem whatever the case may be. – user39367 Nov 3 '15 at 3:43
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    Ok I finally added r410a and the short cycling stopped and it's purring like a kitten. It was much easier than I thought, I know that I was lucky in that respect. Hopefully there won't be any other problems. Thanks everyone for the advice. Happy coming holidays especially x-mas. – Erling Pacheco Nov 29 '15 at 22:08

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