Houghton Heat Pump Upgrade

[VTSweetpea]

Just upgraded to a Houghton Low Profile Quiet HEat Pump from Recpro. Did the install myself. Other than getting the old Dometic unit off the roof and the new Houghton onto the roof, the install was pretty straight forward. So far very happy with the function and quietness of the unit.
However, one thing that I am dealing with is getting my propane furnace to work, since the new HP has a built in thermo controlled by a remote.
The Dometic HP that I took out worked in conjunction with the DuoTherm 5 button thermostat in my coach. Communication between the two was via a phone type cable. Research indicates that all the heating and cooling functions were carried out via a control box in the Dometic HP. This was confirmed when I removed the HP. There was a phone type cable attached to the HP as well as the expected wires for both AC and DC power.
I am going to replace the DuoTherm thermo with a basic analog Suburban heat only thermo to control the furnace.
I'm thinking I can use the wiring in the phone type cable to do this but not sure how.
Any suggestions or experience that you might share?

[chin_k]

The DuoTherm also controls the furnace under seat on the back, so make sure you get a heat-only controller that is compatible with both your Houghton and the furnace. See if the Houghton have a list of recommended controller, and see which one can also be used for the furnace, then you make sure you got the installation manual and confirm the wiring. Good luck.

[VTSweetpea]

Thank you for your response, chin_k.
I guess I wasn't clear, the Houghton doesn't use a separate thermostat. It has a remote that is used to set temp and fan speed. There is an LED display on the interior ceiling plenum that also displays this information. So I don't need a wall thermostat to control it.
I do however need a simple wall thermostat to control the furnace only. I have the thermostat but I need to figure out how to wire it directly to the furnace only. I'd like to use the existing wiring from the Dometic/DuoTherm installation to get from the new wall thermo to the furnace.

If you check the info available on this forum as well as the web, the original Dometic/DuoTherm setup in the Chinooks was a "custom setup" not a standard heating/cooling setup. The DuoTherm talked to a control board in the Dometic heat pump. The control board then turned on the heat pump, AC, fan or furnace based on what instructions it received from the DuoTherm. So I know there is wire going from the wall where the DuoTherm was mounted to the ceiling Heat Pump. And I know that there is wire going from the ceiling to the furnace.
I was hoping that someone on this forum has done what I want to do and can tell me what wires are what. If not, I'll have to do the leg work myself with a meter and open up the access to the furnace.

[chin_k]

You may want to do a quick search and see if there is any existing diagram for the wiring that you need. I do not remember seeing it, however, but don't be discouraged by what little that I do remember.

If you do have to open up the space and do the wire tracing, it will be great if you can report back to save someone in the future that need the info. Good luck!

[caconcourse]

I don't think there are any "smarts" in the phone type cable that ran from the old air conditioner control board to the floor furnace. Most likely a regular thermostat can be connected to the wires in that cable to turn the furnace on and off. You can test it by stripping the wires and connecting them by hand to see if the furnace turns on and off. I think there are only two wires in that cable, but if there are four, only two are actually used.

The other phone-type cable with 4 wires that ran to the 5-button controller is different and had a coded signal between the thermostat control and the air conditioner.

[VTSweetpea]

Clay,
I've pretty much come to the same conclusion. Fortunately, I took pix before I dewired the old Dometic. Along with the phone type cable were several other individual wires. Two blue and a red and black which I labeled (see pic). After watching a boatload of You Tube vids on installing, upgrading and fixing Dometic RV heating and cooling systems, I'm pretty sure the red and black wires are DC power to the furnace and the two blue wires are for the thermo stat. So, as you mentioned, I'm going to reconnect the power wires to the DC source that they had been connected to in the ceiling. I'm going to strip and use 2 of the wires in the phone cable to get to my new wall mount, heat only thermo. I will then power on and see what happens.
Schedule is to do it this weekend.
Will let the forum know outcome.
Wayne

[/img]

[chin_k]

Wayne,
You may want to test the wiring on the furnace end after you made the connection in the overhear area to make sure you wired it correct, if you want to be careful, before connect it to the furnace. Just use the ohmmeter. If you already attached the the thermostat, then power it up, and check the voltage on the furnace side. Just a suggestion, and I am sure you are going to be fine if you want to be more adventurous and power it up without testing.

[Blewett]

The two blue wires on my old furnace were for the thermostat. They were connected to the thermostat by a phone line type cable. Same type of wire used in homes.

[VTSweetpea]

OK, got it sorted. Here's the skivvy. If you look at the pic I posted previously you'll see a cable with 2 small wires (red and white). The pic makes it look like those wires are labeled 12 V+, but that is actually on the large red wire in front of that cable. Anyway, it turns out that these are actually the thermostat wires for the furnace. I confirmed this by holding the two wire conductors together. The furnace started to cycle! These wires had been connected to 2 blue wires coming out of the Dometic control board. (similar to what you were saying Blewett).
So FWIW, the control board in the Dometic AC was the brains of the entire coach HVAC system. The DuoTherm Comfort Control was basically the user input device that allowed us to tell the control board what we wanted- furnace, AC, fan, and heat strips (in my case). The user inputs traveled over the phone type cable (4 wire). The control board then sent the appropriate instructions to whatever device was needed to turn them on. That's why the furnace thermostat wires were run up to the Dometic AC.
I'm describing this in detail for the next guy that tries to figure out the HVAC wiring in his Chinook.
So, in conclusion, it is possible to use the wiring in the phone cable to connect a standard heat only thermostat to the furnace thermostat wiring left in the ceiling after removing a Dometic AC unit with control board. Snip off the phone connectors on both ends. Connect the red and white furnace wires to 2 of the 4 connectors in the phone cable. On the other end at the wall thermostat, connect whatever 2 phone cables you used to the 2 thermostat terminals. In my case the thermostat terminals were actually labeled R and W. Hope this helps someone in the future.
Thanks to all who helped me figure this out.