Help me find- Transformer for RV AC board

Hello and thanks in advance for any help you can provide. Looking for a transformer to replace suspected bad part on a Duo Therm brand RV air conditioner board.

I am missing the 12vdc to the thermostat 90% of the time.

@Jerpois1970, i haven’t found any references from AM-15576, 46-00060-403, 26226. When powered what AC voltages do you see on the primary, and what do you see on the secondary (looks like a dual winding)? A picture from underneath might help.


I will need to look into how to power this transformer to check voltages. I am not that familiar with them So any direction you can give would be appreciated. The pins look to be numbered 1-8 with one side having pins on 1 and. 4 and the other side having pins on 5,6,7, and 8


@Jerpois1970, thanks for the bottom photo, this is wired as a “Center Tapped Full Wave Transformer”, thus 5-6 and 7-8 should be the same AC voltage, just 180 degrees out of phase.


I may be misdiagnosing my issue as being the transformer then. My thought was that the transformer was creating 12vdc from 120vac and that 12v is what is used to power the thermostat and from there pass signal to the relays for fan and compressor at the main ac unit. When the system isn’t functioning it is not able to be turned on at the thermostat. I’ve swapped the thermostat to the other ac unit and it is functional. Also have eliminated the ribbon cable as an issue as there is continuity one end to the other on each line.

Would you be able to provide another picture of the entire top of the board? I’m curious if there’s a regulator or another component that would cause intermittent power. You’ve also checked that the supply voltage to this board is constant and reliable?

Honeywell offers thermostats for both low voltage (24 volts) and line voltage (120 or 240 volts) systems. The most common type of voltage from a central heating and/or cooling system is 24 volts (24Vac).

If your RV uses a standard US household style thermostat system then it likely is not DC powered.

This is a 12v system from an rv unlike a household system.

It has the original Duo-therm thermostat which is supplied power from the rooftop ac unit main board through the ribbon cable. That is then passed back to the main board for signaling fan speed, compressor on/off.

Transformers do not work at all with DC power, they only work with AC.

So if no AC is being supplied then the circuitry must either be creating AC to use with the transformer, or the PCB has other functions that only work with AC power and when run on DC power the transformer portion of the circuits are not used.

To clarify- Supply voltage is 120vac. Either from shore power when the rv is plugged into an outlet. Or from the onboard 7500w onan generator.
I have that at the main board but am missing the 12vdc to power the thermostat which should be coming off the main board.