Hello, first time. I hope I interpreted the rules properly and this is appropriate here.
A contractor installed a Mitsubishi Mr. Slim SEZ-KD12NA4.TH ducted AC/heat-pump system to cool my home office. (I only plan to use the AC — the room has hydronic radiant-floor heat controlled separately.)
The unit's in the uninsulated attic, about 30 feet of ductwork away. The return and both output vents are all in the 18'x15' office.
They installed the (hilariously ugly and unintuitive) PAR-21MAA wired remote to control it.
It cools the room very well, and I can't believe how quiet it is, but it appears that the thermostat is measuring the temperature in the (hot) attic, not the room. This is obviously pretty bad, since it's never responding to the actual room temperature and uncomfortably freezes the room while waiting for the hot attic to (never) get cool.
I've attempted some basic research, but I'm really not qualified in this field. It looks like the temperature sensor is actually in the return-air intake on the unit, not in the PAR-21MAA "thermostat" on the wall.
When they installed it (photos attached), it looks like they cut a 1" gap into the return duct for filter access, and then they hacked together a removable filter by cutting a filter from who-knows-where and screwing two wooden handles onto it. (Feel free to tell me how horrible that is, and if I should have them do it "right", whatever that would entail.)
My guess is that the temperature sensor is pretty close to this open-air gap, and return air is mixing with hot attic air before the temperature is measured, which is why it's measuring so much hotter than the room's actual temperature.
I'm having the installer come back here this week to take a look, but I'm questioning his skill level a bit at this point, and I'd love your input on what my options are and maybe what I should ask him to do. From the product literature, it looks like this unit is compatible with a "Remote Temperature Sensor (M21-JKO-307)" —*maybe that can be installed in the room and take over from the air-intake thermometer?
Alternately, and I know this is a longshot, is there any reasonable way I can just control this unit with the regular thermostat that's two inches away? It looks like it uses custom DC control wiring and is absolutely nothing like standard AC thermostat wiring, but I'd love to get this controlled by the Nest, abandon this PAR-21MAA, and completely sidestep the duct-thermometer issue.
Thanks for your time and expertise.