fish I have 3 geothermal heat pumps with forced air - two in the basement to condition that space and the main floor above and 1 on the second floor. My second floor space has 3 bedrooms plus a small playroom/washroom and is about 1800 square feet. If I could do it all over again, I would have designed the house so that I did not need that second floor unit. Here are the reasons: - The 2nd floor unit and ducts required interior insulated space that was at least 5' x 4'. That doesn't sound like much - but it took a huge dent out of one of my closets. I wound up having to put the HVAC closet in the back of a large bedroom closet and by the time I was done, the usable space in the clothing part of the closet - accounting for the sliding door access into the back HVAC part plus the swinging door access into the front cloths part of the closet - did not leave much room for hanging cloths or shelves. - the vibration from the 2nd floor unit was deafening when we first turned the system on. The scroll compressor generates a lot of noise due to vibrations that came right through the second floor into the main floor. I wound up using vibration dampers on the floor as well as a suspension system to minimize the noise. It is much better but still noticebale. - the ducts for the second floor are in the attic. Even though the ducts are insulated, I am sure I am loosing efficiency with the extreme temps in the attic in both winter and summer. - I really don't like having 2 x 1 inch pipes carrying an anti-freeze running through my walls/ceiling up to the second floor unit. I would prefer all of that pipe and fluid be in the basement. If I spring a leak down there - it would be a pain but easily handled. If I spring a leak on the main or 2nd floor - that would be a huge mess to clean up and would probably damage my floors and other things. - It turns out that my house is so well insulated, I really don't need to run the second floor unit too often and I am thrilled about that. The downside of not putting the unit on the second floor is that you will need to design some space to run ducts from the basement all the way up and distribute to the rooms. That can be much harder than it sounds when you look at the house framing and what will be in the way. And that might jack up the cost of the house. Had I known about these things I would have either designed the house to accomodate ducts to floor 2 OR looked at alternatives like SR suggests. I love the GT system - but floor 2 could have been done better. Just a few things to consider.

Thanks, all. I found the detailed schematics of the indoor units and branch boxes (branch boxes drive the indoor units). Looks like terminals 1 and 2 provide the single phase 220V power supply. Terminal 3 is a serial communication line driven by an IC named HU2001R3. The receiver on indoor unit side is HI2003R3. HU2001R3 is driven by the NEC microcontroller uPD78F1164. I could not find the datasheets for HU2001R3, but it looks like it is a kind of parallel to serial converter and it uses a reference voltage (220V input voltage in this case) to generate the serial output. This means that terminal 3 is also operating at 220V. So, it looks like 3-pole disconnect is needed.

Can you use your old AC blower fan ?

Thank you all for the responses. In short, based on responses here and some more research sounds like it doesn't pay to go with a mini split for a 3200 soft home (that's without the basement) + I think the look is too aggressive and trying to keep a clean minimal look.. even the ceiling cassette units that are relatively minimal stand out a lot... I think ill stick with a gas HVAC system and use coil so the air won't be as dry in the winter and also install a dehumidifier to have it nice in the summer... I did want to have a DAMPER for each room but was told that it can create issues and I need to limit each zone to maybe one or 2 damper tops per zone otherwise the unit can start icing and causing issue as they get "chocked" As for geothermal, My architect did tell me to look into it but once again don't know if it make sense for me. Don't know anyone who has it and its seems like it would be adding a big headache with starting to dig again..... @Ray Austin Thank a lot. I'm hearing this a lot where it will take so many years for me to see a return on investment and probably docent make sense... @mike_home yes I have gas and I will be using gas for the HVAC & domestic water. @Steve Greenberg I was explains that one outdoor unit will be able to handle about 4 zones but it seems per the comments here and other research I did for a house of api 3300 sqf it doesn't make sense finically to go with the mitzubishi + I'm not crazy about the look of them (cassette units) Im also concurred that the. entire house as a whole won't feel as comfortable (temp controlled) when there are so many individuals zones. BTW I was told they can work until -13° but in the nyc area we down really get to those temps.. @fsq4cw I wanted to to floor radiant but its going to be very pricy to do my entire home.. so with no choice I have to let it go.. as for Air-to-Water technology im concurred going with something that is not well known and don't have experience with... @sktn77a this is my findings as well and think I will stick with HVAC and maybe add to each zone (level) a dumper to 1 or 2 rooms per zone. was told that having a dumber in each room can cause the unit to choke and create problems like icing... @tangerinedoor you actually strengthened my fears of being concurred that the entire house or level will not be air conditioned evenly if doors not opened and/or installing another system (CERV)... leading me to stick with HVAC im curious to know how much more expensive was the mini slipt vs an HVAC assuming you got a quote in HVAC. not in dollars and cents but in percentages..