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.
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: