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I have a Mitsubishi Minisplit HVAC system. The compressor is a MXZ-3C24NA2 and the 3x head units are MSZ-GL12NA.

When I pull up the wattage of the compressor I see a "rated total output" of "1,620 / 2,100". When I look up the head unit I see a "maximum power output" I found 1,300.

Is the max total output 2100+(1300*3)=6000? Or is there another way I should be thinking about this?

Thank you!

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  • Can you shoot a pic of the equipment nameplate or link its spec sheet? There are several numbers we need off it, such as "Locked Rotor Amperage" (maybe). Mar 27, 2023 at 19:49

1 Answer 1

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Output (heat or cooling watts) is not what you need here - it's input (electrical) that matters.

Look at the label on the compressor for "minimum circuit ampacity" - if the head units are (as on mine with one head each) powered from the compressor unit, stop there, as it's the thing you'll be powering, and the head units get fed by it.

That MCA or "minimum circuit ampacity" appears to be 22.1A at 208/230V or about (just over at 230V, well under at 208V) 5 KW. But the label on your actual compressor unit may be more accurate than a PDF for what may only be a model sharing most of the model number found on the internet, so let it rule.

As a point of reference, I recently ran a pair of Mitsubishi minisplits with 10.1 MCA (each) at 240V off an 8KW generator (because it was the one I had handy - 5 would have worked fine, without the other loads) with several other loads when the power was out for 2.5 days. Wild claims about starting surge that apply to outdated compressor drive technology just don't apply here. The generator did not even bog down when they started, much less "fail to start them because it wasn't 15-25KW."

A few hints on generators: if you can stand the price bump, an 1800 RPM (for 60 Hz - will be 1500 for 50 Hz) or else an "inverter" generator (variable speed through the magic of making DC to be inverted to AC, rather than making AC directly) is a whole lot less annoying (and generally longer-lived, where you'll get your price bump back in time) than a 3600 (3000) RPM generator. Allow enough capacity to also run your fridge and freezer, which should not take a lot with modern ones; if you have a well, one that will run the pump (perhaps while shutting the heat pumps off) beats having no water. Test-run the generator regularly, i.e. once a month or so.

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  • Yes, it says 22.1A. Should I interpret that 5KW as the peak draw? It is my understanding that the startup draw can be significantly higher than the running wattage, and I am not sure which that is...
    – evt
    Mar 27, 2023 at 2:39
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    Inverter-drive largely means you can ignore startup surge as it's not a significant issue, because the compressor starts at low speed and ramps up as needed. Much softer than a "soft-start" kit on a traditional all-or-nothing compressor. Note that the breaker required is a mere 25A, so litterally the smallest size that's more than 22.1A.
    – Ecnerwal
    Mar 27, 2023 at 2:42

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