I found an online manual for this unit and it talks about defrost and defrost sensor in plain English. It matches up with what you guys have been saying. I have no idea why the tech wouldn't do a simple check on the defrost sensor (apparently because he knows nothing about there even being a defrost sensor). Seems very simple. It really makes me wonder why this company is so reputable. Perhaps it is just this one tech. Anyway, I won't be pressing this as a needed repair with the current home owner - just seems like too much of a hassle since the HVAC company I chose to come out and inspect the unit is saying it is working fine. I already got the defrost board repair out of them and that seems like the more expensive of the two repairs. Once I get possession, I will be able to take care of the issue without any fuss. Thanks again for everyone's help. I hope to report back if that does indeed end up being the issue just for some closure (because I know you are all just waiting with anticipation).