Last week, I had my yearly service performed on my heat pump system. They come out and clean the coils, and check everything to make sure it’s working. This year, though, the tech said there was something questionable, in that the subcool was too high, and that there seemed to be too big a temperature change on each side of the liquid line filter drier (LLFD). So, they suggested a service tech come out, and take a look. Fine, though I wasn’t looking forward to the cost.

Knowing resources are out there, I posted on the hvac-talk forums here, and got some opinions before the tech came out. Alas, the useful bit I didn’t get until after the tech came out. The key bit being: you can’t accurately measure subcool and superheat when the heat pump is in heating mode. So if your maintenance people tell you the subheat or subcool are off, and it’s 40°F out, and your house is being heated, you can PROBABLY ignore them. Obviously if they’re WAY off, it could mean something, but by and large, they’re only relavant in cooling mode. That is all. =)