The ir controller just sends a setpoint to the air handler and it controls off of the air handlers internal return temp sensor. There is way more going on the just you ask it to be 70 and it runs to that and shuts off. There is a deadband of 1 degree c or 1.7 degrees f that when you get into it the unit backs off and coasts so it doesn't overshoot.

Every stat option for the most part will work like this. The exception is he tstat interface the PAC-US444-CN1. It changes the way the internal logic works of the indoor unit and just ramps up the exv and by extension the compressor based on time and distance from setpoint. I think the deadband is still in effect though.

My house has two S series units with smart ME t stats and it's never at setpoint. It will stop short a degree and a half due to the deadband. I just learned to live with it.

At the last DSG conference I was told Japanese people aren't as concerned with the temp being dead nuts on setpoint all day long and a 1 degree c offset is fine and acceptable.

Long story short the ir controller doesn't sense temperature, most stats work exactly the same because it's just (potentially) reporting a return temp to the unit for it to control To based on indoor unit control board logic, and the PAC-us444 is awful.

 

Yea that's basically what I'm gathering. Good info on the deadband, that makes sense. On a cold day I can have the remote at 70 and my actual temp is about 64. But spring/fall I'm usually in line or pretty close. Same with a super hot day, I could have it at 70 and it'll be 74 or 75 if it's probably 95+ outside.

Any chance you could elaborate more on how the internal logic changes with the external tstat? What makes you say the PAC-US444 is awful? Have you heard about the Kumo Cloud interface at all? I'm hoping their kumo blu tooth temp sensor could work as the primary sensor.

Thanks!

 

For the most part with most external thermostats hooked up the logic is the same its just the source of the return/space temp changes to the Thermostat. In the indoor units there is a return sensor and a space set point. With a IR controller you tell the unit the space set point and there is nothing further the controller does until the next time you want to change something. The unit will control itself based on its internal logic. When you hook up a thermostat just the source of the room temperature changes and the tstat tells the indoor unit the same things the IR remote does(Vane position, fan speed, mode, ect).

When you use the PAC-US444 there is a Y1(low cool), Y2(High Cool), G(Fan), G1(Low fan), G2(Medium fan), G3(High fan), W1(Low Heat), and W2(High Heat). Lets say in low cool the EXV opens to 140 steps and refrigerant flows. the interface is going to keep dropping the set point over time to cause the EXV to open farther until the Y1 call goes away. In High cool it will open the EXV to 350ish steps and do the same thing. When Y2 goes away it will close the EXV back to the Y1 level and start dropping the set point. Its not exactly how the indoor units work normally and its sort of a "Hack" to provide a conventional thermostat option.

All of these devices PAC-US444, Kumo cloud, MAC333 with a simple MA or MHK1(On M Series) use CN105 for communication. P series has a TB15 terminal to hook up a wired stat. City Multi is different all together from M series. None of them are going to radically alter the operation except for the PAC-US444.

For what its worth I am a Diamond Service Group Member(DSG) for Mitsubishi and this stuff is super confusing to me and I take calls on it all day long. The best thing to do is look up you model # on www.mylinkdrive.com and/or check the controls section for the device you want to learn about...