i just bought a house built in 2005 with a Trane Heat pump split system, Mooresville, NC. During the fall the unit worked fine, cooled the house nicely. Now that winter is hear I am having issues. I set the thermostat on 70 and during the day it stays warm, but if I try to raise the set point to 72 i loose heat in the house , at night the temps drop below 40 outside and the temp in the house goes to 65'ish and the outside unit freezes up the coils. The auxillery heat comes on but doesn't do much if any good. I manually put it on emergancy heat and the house will heat very nicely. I can unthaw with a water hose and it will work just fine until it gets cold and freezes over again, usually at night. I called a tech out and after about 30 minutes of looking at it said the DEFROST CONTROL BOARD was out and the defrost sensor had a weak reading. He quoted $850 for repair which I thought was crazy since he would not gaurentee to fix the problem. I checked around and found a Trane distributor and for $56 shipped got the parts and replaced in 10 minutes. It seemed to work as the unit would heat to 72-74 without a problem. But it is mid 30's in NC and colder at night and now it is back to icing up again.
I can put the unit into AC mode and run for 5 minutes and the unit defrosts fine. I then put it back in Heat mode and it will heat up nicely.
What else should I check, bad reversing valve? low charge? reversing coil?
I want to call someone out but don't really trust anyone to not overcharge me.
$850 for $56 in parts and 10 mins labor i think is kinda over doing it.
thanks for any help