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BrynP · 09-19-2017, 07:02 AM

Hi all,

Newbie here. I have a 1994 Monoco Dynasty. When I purchased in May from Texas RV Superstore the front AC unit(Duo-Therm 620215) did not work and they replaced it with a Airxcel 48000.

My furnace/thermostat do not function and from what I can tell the new AC unit controls are internal and it do not connect to the original thermostat providing the 12VDC to operate the thermostat that also controls the Suburban furnace(SF-42F).

Does anyone know if the Suburban furnace has a 12VDC power supply to run the thermostat independent from the old AC unit?

Can original thermostat be wired directly to a 12VDC power source?

Any thoughts would be greatly appreciated.

Thanks
~Bryn

BFlinn181 · 09-19-2017, 10:45 AM

Does the rear A/C unit work with the thermostat? Look up your thermostat make and model online and find a manual for it. Once you have the manual, take the cover off the thermostat and check for 12v power. An RV furnace does require 12v to operate, and also a 12v signal from the thermostat to turn on.

BrynP · 09-19-2017, 02:25 PM

The rear thermostat and AC unit are isolated from the front thermostat/furnace/AC unit.

That seems to be my problem, there is no power to the thermostat,I believe the 12VDC was provided by the AC unit that has been replaced. Do you know if the furnace has a 12VDC (r) supply for a thermostat or will I have to find it elsewhere?

Thanks
~Bryn

nehog · 09-19-2017, 05:46 PM

You may find that the (original) unit had just a set of dry contacts for the heat. If this is the case, I'd suggest just using a separate thermostat for heat. You can test this by connecting the two furnace thermostat wires together. If the furnace starts up, then you can do this.

nehog · 09-20-2017, 05:54 PM

Update on what I wrote above.

The Suburban information I have found show the furnace expects the thermostat to have a set of NO contacts that go NC to call for heat. One of the two wires will be +12 volts (internally in the furnace) and the other is the command for heat.

BrynP · 09-20-2017, 09:50 PM

Thank you Nehog,

You are correct, replaced the thermostat. Was able to verify and test before I removed all the no longer needed wiring. Here is Suburban service manual with sequence of operation.

http://www.bdub.net/manuals/Suburban_Service_Manual.pdf

Thanks again
~Bryn