Heat Pumps and Electric Heating - Amana Heat pump PTACstarts to heat then quits

I have an Amana self contained wall mounted heat pump/Ac unit in our sun room apprx. 2 1/2 yrs old.Today its acting up.In a/c mode it works fine but in heat mode it starts to heat and the relays on circuit board start to click and it quits heating. The heat coil only starts to produce heat and relays kick in and out.This goes on for about 5 min and unit shuts down for a few minutes and then the process starts over.I had the heating element up out of unit when running and they never really get very hot due to the fact I think the relays arent engageing long enough.Once in a while during this after I reassemled I could hear a slight cracking sound near the heating coils right before relays click in and out..Only thing other than the coils it looks to have 2 thermal type of cut outs, one on each end of connection points of wiring.Parts should still be under warranty but was wondering if I should replace or spend the service call fee.Are these common to go bad this soon or could this still be a circuit board problem which I know will be way high $
Thanks