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GlennWest

Comfort Control thermostat question

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As you know I doing away with my Dometic unit. Will my thermostat still work for furance when I remove it. It has a box with it that controls the previous 2 different ac units.  Mine is the older tall one, not the long newer one.  The newer ac was used and older one together, so a box to make this work was installed. 

Edited by GlennWest

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Ok, looked at the wiring on line. Furance wire goes to main ac control box. So seems I have to replace with surburan furance thermostat. 

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56 minutes ago, Sehc said:

My suburban thermostat is just a on off switch (thermal spring) to the furnace.

That is all that is needed for the furnace but you will need to route a two conductorlead from the furnace to the location of the new(replacement) thermostat. There are 2 blue wires in the furnace that should connect to the thermostat and when calling for heat they are shorted together. At present that lead is run to the air conditioner. Probably be easiest to run a new one. Telephone type wire is ample for this purpose.

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Thanks. Got to looking and the thermostate wire is in a crawl space and I have  access too. Be easy to do. Glad someting is. 

Edited by GlennWest

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42 minutes ago, GlennWest said:

Shouldn't any 2 wire thermostat work? See some mechanical and digital ones at Lowe's. 

Make sure it is a 12 volt thermostat, since many are 24 volt.

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15 minutes ago, Bill Joyce said:

Make sure it is a 12 volt thermostat, since many are 24 volt.

Or powered by it's own on-board batteries. Opens up the field a lot.

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2 hours ago, GlennWest said:

Shouldn't any 2 wire thermostat work? See some mechanical and digital ones at Lowe's. 

Yes they should. If you just use one of the simplest thermostats it won't be voltage sensitive as they are just a bimetalic spring that expands or contracts to open or close a set of contacts to connect the two blue wires from your Suburban furnace. You can get one made for Suburban from Amazon for $14.

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Problem with the Suburban Stat is the dead band between the starting of the furnace and the shutoff.  We had over a 4 degree swing and it was just uncomfortable.  I replaced it with a battery operated stat from Home Depot and that cured the wide temp swings.

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Some of the modern thermostat, even the simple on/off, need external power. They will not work with the Suburban.

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23 hours ago, GlennWest said:

All the 24 v units i have read reports on said they work on 12v also. Work as low as 8 volts.

The problem with 24 volt thermostats is twofold. The 24 volt system is AC, while the RV is DC. The other problem is most RV systems don't have a ground reference wire at the thermostat location. The 2  wires are only a switched pair.

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18 minutes ago, Carlos said:

Nearly all RV systems are microvolt, not 12/24v, and cannot power a thermostat.  This is what I put in our TT and love it.  Super easy to install, works great, and no wild temp swings any more.

 

https://smile.amazon.com/gp/product/B000ALEBZY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

Sorry, Charlie. The flame sense circuit is micro to millivolt, but the control side is 12 volt. 

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And yet you still use a millivolt system thermostat.  The semantics notwithstanding, you don't have 12v available at the thermostat to power it on most RVs.

 

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I could use a line voltage thermostat, if I chose to. When you refer to a millivolt thermostat, you're referring to a system that uses a thermopile for electricity, and uses no outside electric source. No modern RV furnace runs like that. 

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Just now, GlennWest said:

But if it runs on batteries it should work.

That's the important point, regardless of semantics.  The thermostat needs to run on batteries of its own, and provide a simple contact closure.  The one I linked to meets both of those.  Household thermostats MIGHT be able to run on batteries, and they provide a pair of closure terminals for "on" as well as several other connections.  They will work if the person installing it knows which terminals to use for that.  The Hunter 42999 only provides two terminals so you can't go wrong.

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