Furnace power supply

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
C

Cleatus

New member
Joined
Jan 2, 2022
Posts
3
Location
Missouri
Hey all
I recently replaced our AC unit with a Coleman Mach 15 unit. The unit itself doesn’t require a power supply to the thermostat as the controls are on the unit itself and it is very simple to install. Well being in the mid west and it now being below freezing my wife and I realized when I took the old one out and taped off the excess wires to things like the thermostat we no longer have a control to turn on the furnace for heat. Our heater works great but we have no way of turning it on now. So I’m wondering what I should to to get power to the thermostat or if there is another way to control the furnace??
 
Welcome to the forum
You said you can control it from the unit so you should be able to turn on the heat from the unit. I had one I installed in our bedroom and it had cool air and heat. I think it was a Dometic though.
 
Last edited:
The thermostat sends 12 volts to the furnace to turn it on. It sounds like this came from the air conditioner you removed, assuming it was controlled by the wall thermostat.

Some thermostats control the furnace directly and only require a new source of 12 volts to make the furnace work. Others only communicate with the control box you removed with the old air conditioner and the control box turns the furnace and off. If you can give us the make and model of your furnace and your old air conditioner we can help you figure it out.
 
Rene T said:
Welcome to the forum
You said you can control it from the unit so you should be able to turn on the heat from the unit. I had one I installed in our bedroom and it had cool air and heat. I think it was a Dometic though.
Click to expand...
The new AC unit has its own controls for air but not heat. The AC unit has a separate part you can but to add a heater. My problem is my thermostat doesn’t have a current power supply so therefore I can’t turn on the furnace heater. Just trying to figure out the best way to maybe have an external power source or option to turn the furnace on or get power to the thermostat
 
Lou Schneider said:
The thermostat sends 12 volts to the furnace to turn it on. It sounds like this came from the air conditioner you removed, assuming it was controlled by the wall thermostat.

Some thermostats control the furnace directly and only require a new source of 12 volts to make the furnace work. Others only communicate with the control box you removed with the old air conditioner and the control box turns the furnace and off. If you can give us the make and model of your furnace and your old air conditioner we can help you figure it out.
Click to expand...
Exactly. The old unit was hard wired to the rv and the thermostat and provided that 12v to the thermostat and in turn the heater. I don’t have the old model number unfortunately. But the new AC unit only required being hard wired to the rv not the thermostat so I just don’t have a way to turn the furnace on
 
Take the thermostat off of the wall and see if it has a second line running to the furnace or only one cable going to the roof unit. If it doesn't have a cable going to the furnace you'll have to install one and probably replace the thermostat with one that will directly control the furnace.
 

Honeywell Heating Dial Non-Programmable Thermostat - Ace Hardware

The Honeywell CT30A1005 Heat Only Thermostat has low voltage controls with a snap-action switch for heating systems. This non-programmable thermostat comes with mounting hardware (wall plate included) and does not require leveling. For straightforward temperature control, there's no substitute...
www.acehardware.com www.acehardware.com

Connect the blue wires to it. This is an old fashion mechanical T-Stat on/off no other features NO power needed just 2 wires works well.. You will want to change the anticipator setting I think i set it to maximum (Try both extremes) .

NOTE unlike the older styles that used a mercury bulb. this one cares not about how level it is.. Looks best if it's "Square" to the floor but if it's at 45 degrees. or 90, or upside down. will still work.
 
John From Detroit said:

Honeywell Heating Dial Non-Programmable Thermostat - Ace Hardware

The Honeywell CT30A1005 Heat Only Thermostat has low voltage controls with a snap-action switch for heating systems. This non-programmable thermostat comes with mounting hardware (wall plate included) and does not require leveling. For straightforward temperature control, there's no substitute...
www.acehardware.com www.acehardware.com

Connect the blue wires to it. This is an old fashion mechanical T-Stat on/off no other features NO power needed just 2 wires works well.. You will want to change the anticipator setting I think i set it to maximum (Try both extremes) .

NOTE unlike the older styles that used a mercury bulb. this one cares not about how level it is.. Looks best if it's "Square" to the floor but if it's at 45 degrees. or 90, or upside down. will still work.
Click to expand...
John can you explain what the anticipator is, how it works and where do you make adjustments
 
You've got sound advice from Lou. The thermostat doesn't care where it gets its 12v from, so you can hook up any available 12v source you can find. The potential problem will be the wiring out to the furnace - it may be direct or it may have gone through the a/c control unit you removed. If there were multiple heat/cool zones, it almost surely went thru the a/c controller. If it's direct to the furnace (usually a blue wire), it will work as soon as you hook up a 12v source.

What thermostat make/model is it? That may give us a clue.
 
Without knowing the make/model...

The thermostat only does one thing - that is to operate as an on/off switch.
The only reason some have batteries is because they have a digital display.
The old-fashion ones need no power. The power comes out of the furnace, to the switch (thermostat) and back to the furnace. If the thermostat is on then it completes the circuit and the furnace turns on. If the t-stat is off then the circuit is broken and the furnace turns off.

In your house you might have a mercury switch, but will not work in a moving RV, so RVs will use a bi-metal spring. As the temp increases the spring unwinds and pulls away from the electrical contact. As it cools, the spring winds and makes the contact touch and completes the circuit from furnace to t-stat back to furnace. That is it. Even the fancy electronic t-stats do only this (though they have a computer guided program for when to turn on and off).
You might have had a fancy one before, but you can put in a simple simple t-stat now, or a fancy one that needs AAs.

As mentioned, look for the two wires as these are what connects to t-stat. There is no positive or negative, just connect to the two terminals on the t-stat.
Place the t-stat on the wall, away from a window or cold/drafty place where the t-stat can get a good representation of the room's ambient temps.
 
Cleatus said:
The old unit was hard wired to the rv and the thermostat and provided that 12v to the thermostat and in turn the heater.
Click to expand...
You don't say what furnace you have but either Suburban or Atwood will have 2 control wires from the furnace to turn it on and off that are temperature controlled. Your previous air conditioner took the signal from the thermostat and either controlled the furnace or the air conditioner, based on if you had air conditioning or heat selected by your thermostat. The control from that thermostat was connected to the air conditioner control circuit board where it then determined which was to be controlled. The first thing that you need to determine is whether the thermostat leads from your furnace are even in the area of the present furnace as they may not even pass through that location since the connections were in your previous air conditioner. You may need to run wires between the thermostat and your furnace. Some pictures would help for us to know what you have. A picture of the thermostat and one of the wires to it will be a good start. If there is a pair of wires from the furnace at the thermostat, you can confirm that they are furnace control by just connecting them together as that should cause the furnace to start. You do not need to supply any 12V power to the furnace's thermostat leads as they just connect the 12V from the furnace to the furnace control circuit.
 
Rene T said:
John can you explain what the anticipator is, how it works and where do you make adjustments
Click to expand...
If you open the T-stat (To make adjustments) there is a dial. or a dial like device (pointer?) It's been a while since I adjusted it. What it does is heat the thermostat a bit when the furnace is running. this is to "Anticipate" the heat of cool down I gather. not sure. but it affects how long the furnace runs each cycle. (you wish to maximize that time normally) It comes pre-set for a home system 24 volt AC. you may or may not wish to change that. On Electronic T-stats it's programmed. and often not properly. (you generally can not change it) but on that mechanical one it is adjustable.. As I said one end or the other.. won't hurt anythign if you put it to the wrong end.
 
You must log in or register to reply here.

Latest posts

Members online

Total: 864 (members: 5, guests: 859)

Forum statistics

Threads
131,981
Posts
1,388,598
Members
137,727
Latest member
Davidomero
Back
Top Bottom