Wire new a/c and controller to old thermostat

[melissaburn]

Hi, I had to replace my rooftop a/c and was advised to replace the old analog controller with a digital version. Now I need to figure out which wires coming out of the controller (red, red-white, orange, black) to connect to the wires going to the old duo-therm thermostat (red, green, blue, white) I took pictures of everything I could think of, including (a) old Duo-Therm thermostat cover, (b) inside with cover off, (c) back side of the works, (d) the color of the wires from the old controller connected to the thermostat (wires hanging in the air), (e) the wiring diagram for the old controller explaining the color of wires seen in photo (d), and (f), the wiring diagram for the new controller.

Note that only 4 wires come from the thermostat to the a/c controller. None of the wires for the furnace go there, so I don't need to hook up the furnace thermostat wires to the controller. Many discussions of thermostat connections talk about this but it doesn't matter for my case.

Looking at the thermostat wires, here's what I've figured out:
red = RC
blue = fan something
green = common?
white (slightly fatter white of the 2) goes to the nut marked "Y"

The instructions for the controller say those wires are:
red = 12V+ supply
red-white = 12V+ thermostat
black = 12V-
orange = common

The new a/c is a Dometic Brisk Air II 15K, cooling only, Model B59516
The new controller is Dometic 3316230.700 (wiring diagram attached)

My only guess so far, and it could be wrong, is that the new orange goes to the old green, common-to-common. But, I don't know if the new red goes to the old red or the old white. etc.

 

[JohnGB]

Hi,

I just installed one of these new Domeitic controllers last week.

You said this:

The instructions for the controller say those wires are:
red = 12V+ supply
red-white = 12V+ thermostat
black = 12V-
orange = common

The orange is "not" common, like in DC common, it stands for communication. They used COMM like in communication.

Basically you will not use all your old wires to the old T stat.

You already have + 12 VDC and - (neg) 12 VDC at the old control box that is needed to power the new gray plastic control box. Have you located the old hot + 12 VDC and the neg, - 12 VDC wires at the old controller? Sunline many times used a black stranded incoming wire for + 12 VDC and white stranded wire for - 12 VDC. I'm not sure your older camper is using that same convention and your pics did not show them. And stranded wire is the flexible wire, many tiny wires make up the wire. Not the solid black and white of the romex cable which is 120 VAC hot and neutral.

You are correct, the incoming Pos + 12 VDC goes to the new solid red color wire.

The incoming Neg - 12 VDC goes to the black wire and it needs to go down to the new T stat terminal strip. You just pick a wire out of the old T stat harness and call it Neg - 12 VDC and wire nut the 3 wires together.

You will need and use 3 wires out of the old harness that goes to the T stat. All the colors will not line up, this new control box fits lots of models that are discontinued.

1. The Neg - 12 VDC like I said above, you pick which color you want to use but this goes to the - 12 vdc on the T stat term strip. I think they labeled the term GND for - 12 VDC

2. There is a red with white strip wire out of the gray box is to go down to the T stat. This is T stat 12 volt power. It is NOT the same as the incoming + 12 VDC power on the solid red wire. You pick what color you want to use out of the old harness, this connects to the + 12 V in the T stat Term strip.

3. There is the orange wire which is communication with no label on it out of the gray box. Pick a color for that wire out of the old wire bundle to the T stat and place it terminal strip on the new T stat.

See the pic below, this is for a different Dometic AC unit then your, but is the same control and new digital T stat

In the above pic, I chose these wire colors to go to the 3 point terminal strip on the new T stat as my cable had these colors.

White = neg - 12 VDC (left side terminal), you created this wire at the neg - 12 VDC incoming wire joined to the black wire at the gray box.
Yellow = communication which is the orange wire with no label on it coming out of the gray (middle terminal.
Red = T stat + 12 VDC, this is the red/white striped out of the gray box. (right side terminal)

If this is clear as mud, I have more pics etc, just ask.

Also one other thing, the new T stat is a capacitance touch T stat, there are "no" push buttons on the face of the T stat, you "gently" just touch the 3 selection areas, do not press hard like a push button.

There are 3 foam pads inside that make the contact from your fingers light touch. One of the biggest complaints on this new T stat is people push hard on the touch areas, that damages the foam as they are not push buttons, and the T stat stops getting a signal any more from your finger. Just a heads up to teach everyone using the new T stat to only lightly touch the area.

Here is the 3 foam pads that can get damaged from pressing like a button,

Hope this helps

John

PS Also read the whole manual, you have to setup the new T stat first before trying it use it to sync it. I would have to look at what page it is in the manual, but you have to go into program mode by pressing mode and up and the mode and down arrows at the same time and set two different things.

 

[melissaburn]

Hi John,

Thanks for your helpful response (as usual). However, I don't want to use the new thermostat. Is there any reason why I can't just keep using the old one?

You suggested I could pick what color I want to use from the old harness for a couple things but my harness has exactly 4 wires - red, white, green and blue. The old control box didn't indicate which wires are the 12V+ and 12V- and that's what I'm having trouble figuring out. Of the 4 wires I have and the way they're connected inside the old thermostat, my guess is that t-red is the 12V+ so it would connect to the new controller red, t-green would go to new controller COMM, and t-white would be gnd or 12V- so I'd connect it to the new controller black. Then, I could attach the t-blue to the new controller red-and-white. Does that sound right? Thanks for your help, as always.

 

[JohnGB]

Hi Melissa,

To your first question,

However, I don't want to use the new thermostat. Is there any reason why I can't just keep using the old one?

The short answer is, "no" the old T stat will not work with the new digital control system, at all. The new system uses a totally different digital communication protocol between the gray box and the new T stat. I can explain more, if wanted, but it will not work. In order to use the new gray box control you have to use the new new T stat.

I did a little digging and this is more complex then originally thought to convert to the new gray box control. Your vintage sliver control box up in the ceiling for the AC unit and the T stat is what I believe Dometic called the Bi-metal control system. And if I have the part numbers right of the older system, there was no + 12VDC or - 12 VDC from the camper 12 volt system brought into the ceiling that feeds the silver bi-metal control box. That style control had a mini transformer on the control board and created 12 DC volt circuit run the T stat and the control system from the incoming 120 VAC supply.

Since your silver box control system died, If I have that right, you have to come up with 12 VDC both + and - up into the ceiling from the camper 12 volt system to run the new gray box unit, and the new T stat. And tie into the furnace control

That is the reason you can't find 12 Volts up in the ceiling as Dometic created their own 12 volts.

Do this to help me confirm what you have, Take the cover off of the old silver control box and take a pic of the control board showing the 4 wires to the T stat still on the control board, Try to zoom in to see the Y, RC, G and H terminals

Also there should be a Dometic part number on the case somewhere of the old control system. Take a pic of that.

We also have to deal with the furnace as the old T stat will no longer have power to it and it may not work with the old T stat with no control power from the silver control box. Unless the T stat is mechanical on the furnace interlock. Have to tried the furnace with the roof AC unit power shut off? does it work? Go outside and take the cover off the furnace, there is an Atwood label on there with the part number and revision of that furnace. Need the label pic and an over all pic of it.

Sorry this is so involved, It appears Dometic may not have thought back far enough of the upgrade challenges of the bi-metal system or decided to not support them but this can be made to work.

The one I just installed went into a non ducted AC with manual controls to convert it to the new style and have the fan shut off with the compressor like the ducted systems did as the new T stat has a defrost sensor. In this case, there was no 12 VDC at the ceiling controls either and I have to bring them up to the new control box.

Hope this helps

John

 

[melissaburn]

Hi John,

Well, the good news is the furnace still works with the ac totally shut down, so there's that to be thankful for! So, maybe I'll just end up with two thermostats - the old one for the furnace and a new one for the ac.

I've attached pics of the inside of the old controller. I tried to get the Dometic part number but it's behind wires so I got it from 2 angles. It's printed in black ink on the board and looks like "Dometic Corporation Assy # 3104757.004". There's also a white sticker with the same number followed by "02-910901-B 03144"

I did find a sticker on the outside of the old box that says it's part number 3104998.004, serial number E3131767. But there's also another number close by saying 3104992.007.

Thanks again for your help figuring this out!

 

[JohnGB]

Hi Melissa,

First off, you are very welcome. Glad to help as I can.

You get and A+ for providing great pics of your old control box and the numbers.

With that info, it confirms my thoughts, that older bi-metal T stat control setup created it's own 12 VDC power system. You are right, you are not going to find 12 VDC up in the ceiling at the older control box.

I did a bench test to figure out how much 12 volt power the controller used so I knew the wire and fuse size to run the thing. And to figure out how the new T stat works before I cut into the camper. They gave no power consumption rating or wire size to use. I found it draws 111 milliamps. Well under 1 amp.

In your case, you have to figure out how to get both a +12 VDC and a - 12 VDC wire up into the ceiling area where the new gray control box is going. I also added a 3 amp ATC fuse to protect the small gauge DC wires. Pending your layout and where you can find the 12 volts source and route it to the area, the fuse can go where the wire size steps down to the tie into the new control box. Example: If you tap into a ceiling light that is on a 15 amp DC circuit, run 15 amp wire to the new control box, then install the 3 amp fuse before you tie in the 12 volt power wires to the new control box.

Here is what I did, maybe this can spark some ideas for you to use parts of.


I bought a 5 conductor 18 AWG thermostat cable. Since there was no 12 VDC up in the AC area, I had to bring it there. This camper was all put together (not all apart for a restore) so I had to be creative on how to find and get 12 VDC up there.

In my case, this was on a 2005 T1950 with a non ducted manual AC control. This floor plan allowed me to start at the power converter with the 5 conductor cable. I created a new 12 volt circuit and installed a 3 amp ATC fuse to protect this small gauge wire. Out of the 5 wire cable, I only used the blue +12 VDC and the white - 12 VDC wires at the converter. The other 3 were left taped off.

I was lucky enough to fish the wire up inside a cabinet, to the T stat area. I slit the cable casing allowing the 5 wires to be exposed. I cut the 3 wires in the cable from the power converter that did nothing and abandoned those 3 shorter wires (red, yellow, green) in place. The blue and white I never cut. Then the red, yellow and green I drilled through the cabinet and they are now the start of the 3 new T stat wires up to the control box. See this pic of the joining. Yes, this floor plan also has a separate T stat for the furnace.

The 3 T stat wires went through the side of the cabinet to the new T stat, then the entire 5 wire cable kept going up to the ceiling heading to the AC unit. I drilled a hole out of the cabinet and jumped across the ceiling to the AC unit. Then into the AC unit. Now I had all 5 wires up at the new control box and hooked it all up.

I did not have time to create a more pretty wood painted wire cover for the cable across the ceiling. My friend I was helping with this, asked if I could tape it up. The run was short and I had white Gorilla tape. They were happy so I never made the wood painted cover. See here. The cable run was right over a ceiling seam joint which helped in this case but would work without it

That routing may not work out on your floor plan, but might spark some ideas to build on.

Hope this helps and let us know how it goes.

John

PS good to know the furnace runs on the old T stat. It must be all mechanical on that older T stat.

 

[melissaburn]

Hi John,
Wow, what a nice detailed explanation. I might actually be able to do this! One more question -- if I want to use the wiring to a ceiling light, can I keep the ceiling light in the circuit or must I abandon it? I was thinking to extend the ceiling light wires about 18 inches to the ac well and put in the 3 amp ATC fuse before connecting the 12V+/- to the controller box. Then I can decide where to put the new thermostat.
Melissa

 

[JohnGB]

Hi Melissa,

Thanks again for the good words.

Hi John,
Wow, what a nice detailed explanation. I might actually be able to do this! One more question -- if I want to use the wiring to a ceiling light, can I keep the ceiling light in the circuit or must I abandon it?

As long as the light has live power connecting to it, no remote wall switch, then I see no issues taping into the light 12 volt power. The light itself can have a switch on the light fixture, but the power source stays live. Run 14 awg wire from the light to the AC area. Then install the 3 amp ATC fuse and hook up to the new gray control box.

The issue if the light is on a remote wall switch is, the AC would only work when the light has power to it. Turn off the wall switch and the AC dies obviously. This can be a pain to deal with.

I was thinking to extend the ceiling light wires about 18 inches to the ac well and put in the 3 amp ATC fuse before connecting the 12V+/- to the controller box. Then I can decide where to put the new thermostat.

Yes, you got it. That will work.

Good luck and let us know how you make out. I sense this issue will come up again for others in the future as the older control boards fail and they have to get the new control box. The next generation controls from the Bi-metallic was the analog control. They too are now being discontinued but at least they had 12 VDC power already installed from Sunline to run that analog style.

John

 

[Tinstaafl]

I would just add that best practice would be to place the fuse as close to the power source as possible, rather than near the point of use. Rationale being that if the wire gets pinched or chafed, you want the fuse to pop before the wire gets hot.

That wouldn't be much of an issue if your source is a light circuit and you're using the same gauge wire. The lighting fuse would pop. But if your new circuit is thin gauge, it could get red-hot without blowing that primary fuse.

 

[JohnGB]

Hi Tin,

Glad to see you join in on the discussion.

Did you see/read something recommended or being suggested or not accurate by Melissia or I? I agree with all you have said, not sure how it fits in this case with what was said. Please, point it out if it came across inaccurate.

If this is about how the new control box gets it's 12 VDC power source from the lighting circuit, Sunline often used 15 amp fused circuits for this with 14 awg wire. This all fits I'm sure you agree.

To tap off that circuit it was recommended to use 14 awg wire run from the light wiring junction to the AC area to feed the new control box. Then install a 3 amp ATC fuse at the end of the 14 awg wire to feed the new control box. I may have not spelled that out enough. And yes, this is a point of use fusing I suggested as extra protection. The main power leads on the new control box are about 16 awg or maybe even smaller by eye, but not below 18 awg by looking at it. I can gage them if wanted. And the unit only draws less then 1 amp when all the relays are energized.

Is there a concern there? Yes, it is not a home run fused circuit for this control box. Sunlines practice was to feed the campers that required a 12 volt DC feed at the AC as part of another circuit with no point of use fusing. Even though the smaller feed wire of the Dometic analog control setup could of toasted like you stated. Same goes for the light fixtures, the pigtails are not 14 awg. There is some allowance for short runs of devices they fall under.

Was something missed?

Thanks

John

 

[Tinstaafl]

Apologies John; I skimmed a bit too quickly and was thinking in terms of that 18 gauge multiconductor cable you mentioned. Upon re-reading, I see that you did indeed recommend 14 gauge. My bad.

 

[JohnGB]

Hi Tin,

No worries, all is good.

If anyone ever sees anything I post that is questionable, sincerely, please speak up. I welcome someone checking behind me. I have been around long enough to know, the "human" factor is alive and well, and mistakes happen regardless of the best intentions.

Since we have sort of jumped into late summer with the weather overnight, will be needing the AC to work real soon. What a yoyo with the weather her in Ohio lately.

Thanks

John

 

[melissaburn]

John and Tin! Guess who has a/c?? This girl! I couldn't find a 3 amp fuse but I had a 5 amp so I'm using that until Amazon delivers my 3's. Since I'm not digging into the walls or ceiling, the fuse is at the controller input, though that may not be ideal. For wire, I'm using a standard extension cord that I cut up. I believe it's 16 gauge so I'll have to replace that with 14 gauge along with the fuse. I'm very proud of myself. Thanks so much for your help!

 

[melissaburn]

New thermostat connections for the a/c

For the benefit of those who come along after me, here are a couple of photos and notes I'd offer.
1) Hooking up the 120V AC, the freeze sensor, and the 6-pin connector to the rooftop a/c were relatively easy once you remove the interior cover and take out the 4 long bolts -- which are all that holds the a/c onto the roof. There are many videos out there on this.
2) The hard part is getting the 12VDC to the controller, as John has mentioned. I removed the nearest light fixture, pulled the black (12V+) and white (12V-) wires down a little, added more wire to reach the a/c (should be 14 gauge wire), and hooked them to the appropriate wires on the controller.
3) The 12V+ is the one that needs the 3 amp fuse. In one of my photos, I have the wires connected without the fuse, then I have another photo showing the fuse in there. You make your own fuse holder out of two spade connectors.
4) The 12V- actually connects to both the controller AND the thermostat. This is the point where I had to convince myself I was doing things right because the wire color changes to the opposite and then back again. That is, coming from the light fixture black=12V+ and white=12V-/gnd. But for the controller, black=12V-. Then, again, for the old thermostat wires, white-w-marking=12V-/gnd. So, the 12V-/gnd is white from the ceiling to the a/c, black from that twist-on connector to the controller, and then white-w-marking from the connector to the thermostat.
5) The red-with-white-stripe wire coming out of the controller becomes the 12V+ to the thermostat so, for me, it gets connected to the red t-stat wire.
6) The COMMunication wire from the controller is orange and it went to the green wire for my thermostat.
7) You only need 3 wires for the new thermostat. (Old thermostat won't work, I tried) They're clearly marked GND, COMM, +12V. Don't forget to feed the wires in through the hole in the back of the thermostat. You can see in my t-stat photo, I forgot and had to take the wires off and reconnect through the hole.
I was able to just pull the 4 a/c wires out of the old thermostat, leaving the two furnace wires connected. So, I have the old thermostat for the propane furnace, and the new thermostat for the a/c. Not pretty but it works.

 

[JohnGB]

Hi Melissa,

Thanks for reporting back. This helps others along the way.

You did good sorting this out, good for you!

Have fun camping this season.

John

 

[Nvcer]

Hi I have a 2000 sunline camper what kind of freion dose it take

 

[johnnybgood-SUN]

Nvcer, camper refrigerator’s don’t use Freon.

 

[JohnGB]

Hi I have a 2000 sunline camper what kind of freion dose it take

If you are referring to the roof AC unit, it most likely R-22. If yours has leaked out, most times it is time for a new roof unit. I'm not even sure you can get any any more other then old reclaimed gas. Or if it is even allowed to be used anymore. These where never setup as a repairable gas systems unless you have all the proper Freon reclaiming equipment, the service gages, and add your own valves for service. A fully trained HAVC tech can do this with all the equipment, but you have deal with the leak still and get the old style gas. To hire this gas system work out most times is cheaper in the long run to replace the roof unit. A 22 year old RV AC unit spending money on a service call can be an investment that breaks again soon.

Hope this helps

John