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hiker108's avatar
hiker108
Explorer
Sep 29, 2019

Plus AND Minus 12v from AC to Thermostat

I have a Dometic A/C and a Dometic single zone thermostat. The thermostat requires plus AND minus 12 volts. The schematic of the A/C control box indicates that the plus AND minus 12v come from the power converter and are passed on, thru connectors, to both the A/C control box and also to the thermostat.

Where does the minus 12v come out of the converter ?

If I unplug the plus and minus 12v connector to the A/C control box, the voltage at the thermostat drops out. Why?

HELP!

Thanks

15 Replies

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  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Sep 29, 2019
    The MINUS 12VDC is a 'Negative' from the NEGATIVE Terminal supplied by battery...either at converter Battery Negative or Battery Negative post.
    NOT a 'Chassis Gound connection.

    Wire bundle coming out of control box......
    MINUS 12VDC is the BLACK wire
    POS 12VDC is the RED Wire
    Furnace are the TWO BLUE Wires
    Load Shedding are the TWO YELLOW Wires (Used with a EMS---Energy Management System Control)
  • hiker108's avatar
    hiker108
    Explorer
    Sep 29, 2019
    The pic I have posted shows the external plus and minus 12v into this unit and same outgoing to thermstat. I suspect that schematic may be incorrect. It may be that this control unit generates the minus 12 volts for the thermostat. I will try to post pic of thermostat wiring.
  • jkwilson's avatar
    jkwilson
    Explorer III
    Sep 29, 2019
    hiker108 wrote:
    I have a Dometic A/C and a Dometic single zone thermostat. The thermostat requires plus AND minus 12 volts. The schematic of the A/C control box indicates that the plus AND minus 12v come from the power converter and are passed on, thru connectors, to both the A/C control box and also to the thermostat.
    F
    Where does the minus 12v come out of the converter ?

    If I unplug the plus and minus 12v connector to the A/C control box, the voltage at the thermostat drops out. Why?

    HELP!

    Thanks


    I’m not sure if you are confused or just using the wrong terms. There is no minus 12V in an RV system. Minus 12V would be 12V below zero or 24V below your 12V output. This is different from the 12V negative (from battery negative) and 12 positive (from battery positive) leads that make up the RV 12V system.

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