mini split a/c unit

[Copperclad]

Any of you guys ever install one of those mini split type a/c systems that operate several indoor units off of one outdoor unit?
This particular bldg. will be finished block as interior walls, so we need to slab all that we possibly can, to prevent having to surface mt. conduit and boxes.
Would I be right in thinking that all the indoor units would operate off of one common ckt from the outdoor unit?. Im thinking the outdoor unit would have to run continuously and the indoor units controlled from a remote?
Or how would the controls tie in?
I guess what im asking is, should I daisy chain a conduit from the outdoor unit to all the indoor units, or maybe a homerun from the outdoor unit to each indoor unit?
Any advise on this install would be apprecitated!

 

[charlietuna]

All that we have run into have the feed to the inside unit, with power and controls going to the outside unit from the inside unit.

 

[kwired]

All that we have run into have the feed to the inside unit, with power and controls going to the outside unit from the inside unit.

I would talk to the HVAC installer, have not seen the system you are describing but have seen similar situation with commercial refrigeration where one compressor cooled more than one retail display case. Each case had its own thermostat that controlled a solenoid valve in the refrigerant line. This allowed refrigerant to flow and commence cooling. If all units happen to be "off" then pressure in refrigerant system rises and compressor shuts off with a high pressure switch.

In that set up compressor and cooled units are electrically independent of each other, but I can also see the possibility of control wires between the units.

 

[nakulak]

I've only installed the mitsubishi units - they have one indoor evaporator to one outdoor compressor, I haven't seen units with multiple indoor units.

 

[EBFD6]

You definitely need to get the specs on the exact units you will be wiring as I have seen them done many different ways. Some units you feed the outside unit and then run a 3 wire to the inside unit. Some are home run from each inside unit to outside, some are daisy chained, some systems the inside and outside units are fed independently power wise with a belden cable daisy chained for controls. It depends on size, model, manufacturer. There is no easy answer other than get the specs.

 

[mcclary's electrical]

I've only installed the mitsubishi units - they have one indoor evaporator to one outdoor compressor, I haven't seen units with multiple indoor units.

The few Mitsubishi's that I've seen can have two indoor units for one outdoor unit. There is a control wire between the two, but the circuit gets fed from panel, not outside unit. You need a switch by the inside unit.

 

[macmikeman]

I've wired probably about at least 5000 split system ac's. They are very popular around here, I have 5 single zone splits at my house in fact. Three major brands are Mitsubishi, Fujitsu, and Sanyo. Before, the Mitsubishi's needed separate circuits run to compressor and indoor units, and connected together via low voltage three wire t-stat cable. Now all three brands you take power to the compressor first, and that gets connected to each indoor fan coil with a three wire control with ground (NM cable) or conduit. There are one to four fan coil systems available. They are called single zone, dual zone, tri zone and quad zone compressors. If you are wiring 9,000 btu fan coils or 12,000 btu ones into bedrooms, and are on 2005 nec, beware because those are 120 volt powered and therefore you need ark-fault breakers so plan on the expense. Same and more if you are on 2008 code. The larger units- 15,000 btu and up are 240 volt and so are the fan coils. Will you need a separate disconect for the interior fan units? Check with your inspector first. For myself, I use a lockable disco on the compressor outside. AC guy comes to fix, locks out exterior disco in the off position, and the interior unit is prevented from energizing although out of sight of the disco. If your area requires the interior disco, then a 3 pole switch in a standard single gang nail on box will work, but they are costly. Another company NG? I have done one or two. That one is a good unit, but it has a proprietary prefab control cable with connectors on the ends for the fan coil connections. Another type is Tadaran, an Israel company and that requires 5,7, or 9 wires between compressor and coil depending on model and (best part) the number changes on some of the wires from the inside unit to the outside unit so you need to pay attention to the schematic when connecting.
Ask away if you have any other questions.

 

[mcclary's electrical]

I've wired probably about at least 5000 split system ac's. They are very popular around here, I have 5 single zone splits at my house in fact. Three major brands are Mitsubishi, Fujitsu, and Sanyo. Before, the Mitsubishi's needed separate circuits run to compressor and indoor units, and connected together via low voltage three wire t-stat cable. Now all three brands you take power to the compressor first, and that gets connected to each indoor fan coil with a three wire control with ground (NM cable) or conduit. There are one to four fan coil systems available. They are called single zone, dual zone, tri zone and quad zone compressors. If you are wiring 9,000 btu fan coils or 12,000 btu ones into bedrooms, and are on 2005 nec, beware because those are 120 volt powered and therefore you need ark-fault breakers so plan on the expense. Same and more if you are on 2008 code. The larger units- 15,000 btu and up are 240 volt and so are the fan coils. Will you need a separate disconect for the interior fan units? Check with your inspector first. For myself, I use a lockable disco on the compressor outside. AC guy comes to fix, locks out exterior disco in the off position, and the interior unit is prevented from energizing although out of sight of the disco. If your area requires the interior disco, then a 3 pole switch in a standard single gang nail on box will work, but they are costly. Another company NG? I have done one or two. That one is a good unit, but it has a proprietary prefab control cable with connectors on the ends for the fan coil connections. Another type is Tadaran, an Israel company and that requires 5,7, or 9 wires between compressor and coil depending on model and (best part) the number changes on some of the wires from the inside unit to the outside unit so you need to pay attention to the schematic when connecting.
Ask away if you have any other questions.

Thanks Mac!! Good Post.

 

[Len]

ductless split

ductless split

We install Sanyo units. The power is sent from outdoor unit to the indoor units....

 

[btharmy]

Highly recommend get the specs. We quoted a job for a unit in a 3 story building. Computer rooms served by two units on 1st floor, condensor on the roof. Mitsubishi units we were accustomed to were fed separately from the panel then connected by control wire by mechanical contractor. Not this time, Had to feed rooftop unit then from rooftop back down to first floor to each fan unit. Lesson learned. 200ft of 12/3mc over estimated amount.