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4-conductor cable. control information.


First time poster.

I have searched the web for this information and have come up short.

I am a controls guy and get to integrate lots of cool discrete units.

On a mini split heat pump the indoor units "talk" to the outdoor units via the 4 wire control cable.

The four wires are, ground, AC, AC and Control.

So one wire for the control to turn it on and off and ask for heat or cool.
Does anyone know if this is level based ac, serial coms, or something else.
I could go in and test the wire but I'm not able to access that right now.

I did control one system by mimicking the IR remote and learning all the settings and then sending the IR signals to each unit from a PLC. This worked for 4 years but has too many moving parts. Simple is better.

Any thoughts?



  • Jamie Hall
    Jamie Hall Member Posts: 23,436
    I suppose that some of the very latest and greatest systems will use a serial bus -- similar to the CAN bus on recent cars. However, in most systems it's going to be a lot simpler -- in fact, it may be (and often is) as simple as a closed circuit in the controller, either raising one of the outputs to a given voltage (usually 24 volts in our trade) or dropping it to ground. Furthermore, in almost all cases your looking at plain vanilla 60 hz AC.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England