Minisplit prep Q

[sands35]

Currently working on wiring for a garage build. Building is up and water tight. Open frames on the inside and laying in the electrical.

32x26 wtih 10' ceilings in SW Michigan. Radiant in floor heat for the winter, so only really need cooling in the summer.

I have a 30 amp AC disconnect I was going to mount on the outside before I insulate and button up the walls with drywall. Might as well run 10-2 on a 30 amp breaker to it now. I suppose I can get away with 12-2, but might as well put in 10-2.

Most of the manuals I've read on these things call for a 20amp 240 circuit. Correct?

Do I need to make any provisions to the interior unit? Most seam to have power, control and refrigerant lines self contained in the installation kit so the power for the inside unit comes from the outside condenser. Correct?

Any recommendations on sizing? Garage will have r13 walls and r30 ceiling. Is reasonably well shaded and only one 4x6 window. I'd place humidity control over air temp. A "hot" day hear near the lake is 85. the calculators say a 18k unit, but I've heard that smaller ones works OK too.

 

[theoldwizard1]

If you button up the walls, where are you going to run the refrigerant lines ?

What are you going to use as a heat source for your radiant floor ? Mitsubishi is now selling a heat exchanger option for radiant floor heat for some of their mini-split heat pumps.


P.S. Larger than necessary wire is NEVER a problem except in your wallet.

 

[sands35]

It will be a year or two before I install the AC unit. Need to pay for what I haven't yet done.

I figured I'd run them on the outside just like everybody else does for a old work installation. Though I have debated installing a 2" LB box to provide a route, but I don't know the OD of all the lines between the two units.

I'd mount the evaporator unit on the inside and the condenser on the outside of the same wall, so the runs can be really short.

 

[JakeKohl]

You pretty much have all you need here. I think some of the Mitsubishi units require their own service to the indoor unit but most others draw power from the small wiring to the outdoor unit.

My 18kBtu LG units required a 25 amp breaker but 12AWG was sufficient (peak loads vs. typical draw). No harm in 10AWG.

 

[sands35]

Thanks. I was thinking that if i have any 12-2 left, i'd make a run to where i'd put the indoor unit just in case.

 

[Riley]

Mr Cool has power fed from the exterior unit through the control wire set. I ran the line set and control wire in 3" pvc which was plenty of room for everything.

 

[Jackfre]

Agreed that the 10 wire is better. Between the condensing unit and the evaporator you want to run 14-3 w a ground. They are very simple to wire between them 1-2-3 on the condensing unit goes to 1-2-3 on the evaporator, plus your ground. 1&2 are the 240v power to the internal unit. 3 is a control wire and feeds back thru the #2 leg to complete its circuit.

System amperage is dependent upon size of unit and manuf. My 12k btu Fujitsu takes a 15 amp circuit. The 15, 18's and I think 24 take a 20 and the bigger singles and multis a 30.

 

[JakeKohl]

Just as an FYI, the LG units require an 18 guage 4 conductor cable (with ground) between the outdoor and indoor units (this also provides power to the indoor unit). You may want to at least figure out what type of unit so you can narrow down the wiring required.

 

[tomphot]

Just as an FYI, the LG units require an 18 guage 4 conductor cable (with ground) between the outdoor and indoor units (this also provides power to the indoor unit). You may want to at least figure out what type of unit so you can narrow down the wiring required.

I'm installing an LG unit now. The instructions are really bad btw. I noticed that it appeared that the 4 wire line between the in and outside units called for 18 guage. This didn't seem correct as that wire is where the inside blower gets it's power.
I called LG and they told me that it needed a 14ga wire. Also, if you look at some of the line sets sold online, they come wired with 14ga.

 

[sands35]

Hmmm.... sounds like I should run a pair of 14-2 between the units. (or a least install a conduit for the wires.)

 

[tomphot]

Hmmm.... sounds like I should run a pair of 14-2 between the units. (or a least install a conduit for the wires.)

The instructions show that the 2 copper lines, the condensation line and wires can all be run in the same bundle. The sets that you can buy on line show the same thing. You will need the 220 outside to run the compressor.
BTW - LG says you can use stranded or solid for the wires that run between the units.

 

[JakeKohl]

I'm installing an LG unit now. The instructions are really bad btw. I noticed that it appeared that the 4 wire line between the in and outside units called for 18 guage. This didn't seem correct as that wire is where the inside blower gets it's power.
I called LG and they told me that it needed a 14ga wire. Also, if you look at some of the line sets sold online, they come wired with 14ga.

well...huh. I was a little surprised that it called for that small so I used 16 gauge solid conductor. Interesting that they told you 14. The manual clearly indicated 18. Mine have been running for about a year so I guess it's staying. I don't think I taped it with the linesets so if I have a problem I guess I can fish it out. The indoor unit is powering a pretty efficient blower and a DC circuit board - it shouldn't draw THAT much current.

 

[Highbeam]

well...huh. I was a little surprised that it called for that small so I used 16 gauge solid conductor. Interesting that they told you 14. The manual clearly indicated 18. Mine have been running for about a year so I guess it's staying. I don't think I taped it with the linesets so if I have a problem I guess I can fish it out. The indoor unit is powering a pretty efficient blower and a DC circuit board - it shouldn't draw THAT much current.

That should be a safety recall. If they indeed require 14 guage but the spec calls out 18 then you have a fire hazard in your walls. People could die.

 

[monkeyspanners]

Usually do the interconnecting in 1.5mm2 4 core, not usually a lot of current going down it, more a communication wire. Depends though on make and model and if its power to indoor or outdoor unit. LG instructions were never much good once translated from Korean or where ever they are made.