Adding a c-wire to a mastertrol system.?

I have a mastertrol HVAC system. I would like to install a new thermostat with wifi abilities. There is no c- wire. Each zone thermostat has extra wires in the bundle. Can I connect an extra wire from the each of the 3 thermostat bundles to the c terminal as seen on the bottom left of the diagram to act as a c- wire? If not, can I get a c-wire plug in adapter in the basement to power all 3 zone thermostats by connecting an unused wire to it and then the c terminal on the thermostat? I just don't want to have an adapter plugged into the wall and connected to each of the three thermostats if I don't have to.

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2 Answers

  • 6 months ago

    Just to be clear, the C you need originates in the HVAC unit, the C terminal is opposite end of "24 volt transformer" that supplies R to the MM-3. You can use an extra wire in the zone stat cables only if you have a spare wire from the MM-3 Controller to the HVAC unit. There is no terminal shown in the MM-3 for the C, you will just need to use a small grey or blue wire connector or crimp connector in free air.

    Identifying the C in the HVAC sometimes can be a little tricky, it isn't always marked "C", sometimes marked common, 24v com, or 24N. If you can't identify it post a picture of the control board in the HVAC unit in a new question.

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  • elhigh
    Lv 7
    6 months ago

    An unused wire that goes all the way from the 'stat to the unit should be fine. Establish a Common connection with that and you should be good to go.

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