Furnace Thermostat wiring question

[Chris00WJ]

I know most of you likely dont have a furnace in your Teardrop or tiny trailer, but up here in the great white north it's pretty much mandatory, even with decent insulation.

Anyways, I lucked out BIG time today and picked up a FREE hydroflame furnace (and fridge, stove, sink, converter etc, but thats another story ). Unfortunately it's had the wires cut and didnt include the thermostat. Now there's only 3 wires. They are labeled Thermostat (white wire), 12vdc + (red) and 12vdc -. Seems simple enough. But every digital thermostat etc that I find seems to be either a 4 or 5 wire setup.

Anyone have any suggestions for a replacement 3 wire setup?

I cant seem to figure out the model number. Even the sticker on the furnace just has a chart with all the model numbers listed and their specs.

[Shadow Catcher]

I used a Johnson Control commercial (remote thermocouple) thermostat which will control both the AC and the Pelonius, but one thing to remember because it has more wires does not mean you have to use them or that they are hooked up to anything.

[Trackstriper]

Here's something I came across several month's back. I don't know if it will help any, but it is an interesting concept and the wiring colors may help you sort things out.

http://www.klenger.net/RV_General/HVAC_ ... ctions.pdf

[Dale M.]

Basically you need to know what furnace requires ... Maybe its as simple as a two wire circuit, and all it requires is "closed contacts" for heat, open contacts for no heat..... IF that is case most thermostats can supply the needed contacts, if using new digital just use contact set the are "heat/no heat".... Just forget features like AC or Auto fan or or whatever if the do not apply for your application ...

Actually I would opt for older mechanical thermostat (two wire) if possible.... Programming some if these digital things are a pain in the rear.... And digital ones require backup batteries....

Your situation is probably the 12volt (+ and -) are power to thermostat, and the white wire is the control.... Only real question would be if the white wire gets +12 volts or -12 volts (ground) through thermostat contacts to turn on heater....

Have you looked inside heater to see if there is any wiring instructions glued inside cover...

Also there is the option of going to any RV web sites that handles the heater brand/model and getting a "matching thermostat"...

Dale

[astrotrailer]

I installed a Atwood Hyrdoflame last October. The thermostat had two wires. 1 wire goes to 12+ volts from
the battery. The other goes to the thermostat wire on the furnace. You can buy the Atwood thermostat for $19.

http://tinyurl.com/2fpy9fl

I bought the furnace from the company in the link.

[Engineer Guy]

See page 7 at this Link for Hydroflame Furnace wiring diagrams; a little tough to read:

http://www.docstoc.com/docs/20282417/Hy ... ace-Manual

The BLK wire goes to Ground [Battery Negative]. The RED wire goes to +12 VDC [to power the Furnace] and to one 'side' of the Thermostat. The WHT wire goes from the other side of a 2 wire Thermostat back to the Furnace and closes a Fan Control Relay to start the heat cycle. The RED and BLK wires carry ~8 Amps or so, so match the size of those cut wires. An internal Circuit Breaker prevents over-current draw. The WHT wire carries low current; only enough to energize the coil of the Fan Relay. Don't attempt to run a heavy RED wire to the Thermostat. Wirenut thinner wires off of the heavier RED wire connection made directly to the Furnace +12 VDC and 'back' to the Fan Relay WHT wire connection. You likely know this already. Schematics can be misleading if someone else takes them literally. Big Box stores sell small diameter Thermostat wire, or recycle what's laying around [Telephone or Doorbell wire, etc.].

If the Normally Open [N.O.] Sail switch is closed because the working Fan is creating a draft, AND the Normally Closed [N.C.] Limit Switch is not open due to over-temperature [usually due to Fan failure], the Module on the Schematic right side will open the Gas Control Valve. It will also fire the Ignitor [which resembles a fine wire Spark Plug] to ignite the Propane. Pretty standard, electromechanical control 'stuff' used for years, and identical to the Furnace in my '83 Avion, as well as the Hydroflame Furnace in a borrowed Tent Trailer. In older Furnaces, a Normally Open snap switch Sensor closes to confirm the Gas is lit by sensing a hot plenum or combustion chamber. This closure provides +12 VDC to the Control circuitry. If the Thermostat still calls for heat, this N.O. Sensor will open and close as the Fan 'cools' it down to closure. This cycles the Propane flame on and off in some Furnaces. In newer Furnaces, a Sensor confirms lit Propane to the Control Board for safety and for flame cycling. 'Dinosaur Electronics', for one, sells P.C. Boards to prevent older Furnaces from continuous, Battery-draining attempts to light the Flame when a Propane Tank is empty. Their Board tries 3 times and quits until +12 VDC is power-cycled and reset. Good folks.

http://www.dinosaurelectronics.com/

You can hook up the RED and BLK wires to a +12 VDC Battery or Power Supply/Charger for bench testing. Manually connect the WHT wire through a ~2 Amp Fuse if you like - for electrical short protection - to the RED wire +12 VDC. This will simulate a Thermostat closing and calling for heat. Safely hook up a Propane Bottle to see that the Furnace actually works and heats prior to installation in tight quarters. Consider cleaning up various contacts before installing the Furnace. Pink pencil erasers clean up PC Board 'fingers' well. Non-metallic 'Scotch-Brite' or disposable 'orange' fingernail files work well on 'burnishing' old Relay contacts or other tight connections. Suspect N.O. and N.C. Sensors can be tested by heating them with a match while connected to only an Ohmmeter.

Many Home Digital Thermostats run off of +24 VAC control voltage from a Transformer - sometimes mounted outboard to the Furnace - stepped down and rectified internally to low voltage DC. These internally-powered Home Thermostats won't work with this Furnace. Use a good ole mechanical, bimetal Thermostat without a level-sensitive Mercury Switch, or a Digital Thermostat made for +12 VDC RV applications.

This Website tells me that plenty of folks are trying to troubleshoot a Furnace, so this is why I supply the operating details above:

http://www.rvmechanic.com/current_categ ... _full.html

http://www.google.com/search?hl=en&q=hy ... =&gs_rfai=

Congrats on scoring the great Trailer stuff!

[astrotrailer]

+12 volts goes to a fused +12 volts from battery.
-12 volts goes to negative battery terminal (ground)
Buy the Atwood thermostat I referenced in previous post.
+12 volts fused from battery goes to one wire of the thermostat.
2nd wire from thermostat goes to white thermostat wire on furnace.
The thermostat has a on/off switch and a temp setting.
Turn thermostat to ON and push temp to warmer until furnace kicks on.
I presume you already hooked up the propane. After about 30 seconds
the furnace will light.