mini split circuit function

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maarkus

Joined Jul 23, 2020
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It's very easy for me to understand an old school analog Tstat wiring scheme. The 24v supply from the transformer gives a power source to the Tstat and it channels it back on unenergized wires to relays that start the compressor/fan and reversing valve in a heat pump setup for cooling or heat. Correct me if I'm wrong here.

On my mini split heat pump system I have three terminals from the outside coming to the interior mainboard. One is 120v, one 111v(?) and the third is 120v along with a ground. I'm confused how the cool/heat signal gets sent back to the compressor/fan and reversing valve on an ALREADY ENERGIZED line. Wouldn't there have to be two unenergized lines going back to the outdoor unit analogous to the old school setup, one for the compressor/fan and one for the reversing valve that could then be energized from the interior mainboard when cooling or heating is desired? I don't see why the interior mainboard would need more than one energized 120v line. I understand the blower motor is DC so it doesn't need a separate line. Regarding the 111v, is that normal or a sign of a problem with the external MB?

It also seems that the compressor/fan signal and the reversing valve could be sent as 24v signals to the relays outside similar to the old school setup but I understand you don't want to mix 120v with 24v in the same conduit.
 
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