Leftie, sorry I'm late to the conversation -- I've been off MNL for a while, focusing on green energy projects at home. If it's not too late -- or if the Mr. Cool equipment needs to be replaced anyway -- could you swap the entire unit out for either a Mitsubishi or Fujitsu wall unit? The equipment on those units is priced comparably to a Mr. Cool, but they have much better low temp performance, supposedly better reliability, longer warranties in most cases, and most importantly, much higher COPs at all the relevant winter temps (47, 17, 5, -5, etc).
You mentioned further up in the thread that the local installer charged outrageous prices for either Mitsubishi or Fujitsu equipment. That's been my experience too down by NYC (and I think it's true most places these days), but I eventually found a small (1-2 people) local HVAC shop that installs Fujitsu hyper heat units for $3,500 per unit total installed cost. That's not too bad when you figure the equipment itself (evaporator, condenser, line set kit, etc) costs around $2,000 - $2,500 per unit online. It took me a year to find them -- everyone else around here wanted $6,000 - $8,000 per unit, and they all tried to talk me into oversizing the units, putting a wall unit in every single room, putting duct work and air handlers in our unconditioned attic, etc. But I now have two Fujitsu hyper heat wall units -- one 9k btu and one 15k btu -- in our two-story 1500 sq ft house (total installed cost was about $7,000). The 15K unit, which is in our dining room, basically heats the whole house by itself, with a minor assist from the 9K unit. We've all but stopped using our gas boiler. I'm not sure which Mr. Cool unit you have - I came very close to going with those myself. But after considering their winter COP data, and considering that even with the DIY Mr. Cool unit, I'd still have to hire an electrician to wire it and still have to hire an HVAC company to purge the line sets, the Fujitsu units actually cost less in the long run.
Here are the specs on the 15K Fujitsu unit that we have. The most important info for me is COP at 47 F, since the average temp in my area during the September - May heating season is 46 F. For Mr. Cools, I believe the COP is around 3ish at 47F, whereas with the Fujitsu units it's at around 5. I did a Manual J on our house and based on a whole house heat load at 47F of around 11,000 btu/h, the average COP of this unit is around 5.5. We're on track to use only 3,000 - 3,500 kwh to heat the house during that nine month season. Our 99% outside design temp is 11F. The attic is insulated to R-49, the basement walls and rim joist to R-10, but there is no insulation in the walls and the house is extremely leaky (100 years old, CFM is still at around 3600 after some piss poor air sealing).