[jeff5may]

Up until around the turn of the century, pretty much all of the mini-splits used cap tubes to do their bidding. Some of the multi-zone units used a txv for heating mode. The more modern units are being built with electronic expansion valves and proprietary superheat control.

The vintage units that work very much below 0 degC actually have 2 cap tubes in them. The first cap tube does its job all the time. The second cap tube is plumbed in series with the first, with a parallel check valve that bypasses it during the cooling cycle. The added restriction of the second cap tube raises the temperature split (delta T or dT) between the indoor and outdoor heat exchangers to allow the unit to extract heat at low outdoor temperatures in heating mode.

I will start using this unit the way it is rigged right now. Once I figure out how well (or poorly) it performs, I may end up modding the refrigerant loop to make it work better. This particular unit has the cap tubes directly brazed into the evaporator tubes, so it would be difficult to plumb in a txv for heating cycle. I'm not sure what I will do yet.