Trane is the same product if you have a good Trane dealer. What's "kicked the bucket" about the compressor? Locked up? Not pumping? Shorted? This isn't rocket science. All the defrost board does is pass the "turn on" signal to the compressor. Really easy to tell if that is keeping the system off. Last year I went on a call that one of 2 compressors in a high end Trane was locked up. It was til I put a high voltage wire back on the terminal it was supposed to be on. Popped right up. Thieves.

Thank you all for your replies. I did download the installation manual, and after mapping out all the wiring, I found out why the pump was always defrosting and corrected it, along with some other wiring mistakes, and I replaced his wires twisted around the relay terminals with proper spade connectors. I also found a dip switch on the thermostat that was causing the 2 minute delay. However, I couldn't find an exterior thermostat as ziggyhere mentioned, but the heat pump's wiring diagram shows a temperature sensor; could the old system have used that as the outdoor thermostat? If not, my parents are on a dual rate from their power company: they get a discounted rate as long as the outside temp stays above -12 degrees Celsius or around 10 degrees Fahrenheit. The power company installs a temp sensor in a housing that mounts between the meter pan and the meter itself, with 24 VAC present at the furnace when the temperature is above the setpoint of 10 degrees. Could the old system have been using the signal from the POCO sensor to shut off the heat pump and switch to oil? Also, when the temperature outside was around 16 degrees Fahrenheit, sometimes the oil burner would come on for a couple minutes (and the heat pump would shut off), and it doesn't do that anymore; could that be a feature of the old system, or could it be a feature of the heat pump itself? Also, with the old system if we raised the thermostat's setpoint even by a few degrees, the oil burner would kick in until the desired temperature is reached, but the new system doesn't do that; is it typical of dual heat systems, or was it just a feature of the old system and I shouldn't worry too much about it? Finally, I have heard and read several times that below a certain temperature, heat pumps lose their efficiency and there was indeed a chart in the heat pump cover, but after 21 years out there, it isn't legible anymore. It's an ICP 2-ton unit, if that matters. Because the system would often rely on the oil burner past the 16 degree mark, I assume that is where that particular heat pump starts losing its efficiency. Is it putting more strain on the compressor to let it run below that threshold? Thanks again for taking time to help me, and have a nice day!

Some people may disagree with me, but I think alot of preventative maintenance is a waste of money. I believe if its not broke don't fix it. I would rather not have people tinkering and possibly breaking/sabotoging my equipment when it is working fine. Its another story if it is broken or not working correctly. Homeowners should replace air filters often. I would recommend only calling for service for a heatpump/ac if the output temperature rise/drop is low or making weird noises. Its easy to test this. Just invest in a digital thermometer from ebay/amazon and stick into the vent when its been running a while.

I would suggest putting the sensor in the freezer for some time and then measuring its resistance immediately when placed at room temperature. Continue to measure resistance over time, say 1-hour at room temperature. There should be a change in resistance as the sensor warms up if it’s purely resistive. If there is no change, if it is and remains ‘Open’ (high resistance) or if it is and remains shorted (low resistance) then there is likely a problem with sensor. Which fan are you talking about, the fan coil blower or HP fan? It’s normal that the HP fan does not run during defrost but the compressor does. IMPO SR