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Old 10-03-2019, 10:37 AM   #1
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Upgrade suburban furnace thermostat(?)

I have on hand a basic, non-programmable (2 A Cell) Honeywell digital thermostat that was installed on my home (gas) furnace/AC system...replaced with a programmable T'stat. I'd like to use it to replace the virtually useless thermostat that controls the Suburban furnace in our Apex 22QBS. The two wires for the Suburban are connected to "R" & "W". It seems to me a simple "remove, wire, replace"(?). The Honeywell is a "PRO TH311OD, incidentally -- pics attached. ...anyone out there who might be able to confirm, add warning or just share expertise? Thanks!
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Old 10-03-2019, 04:58 PM   #2
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OK -- I can now answer this. It works...perfectly. And, while it's essentially a "make-do" (...can't utilize the "fan on" or "AC control" functions), it controls the room temp & furnace on/off very well. The furnace is simple 2-wire, so the change out was easy...took every bit of 15 minutes. I'm already thinking that there's gotta be a simple (relatively) way to also utilize the AC "side" to control the temp (compressor on/off) from the roof AC -- will report back.
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Old 10-03-2019, 05:16 PM   #3
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Was the prior thermostat both for AC and heat? Or just heat? If both, you should be able to make it work. Or do you have to use controls on the AC unit heat in the ceiling to adjust your AC?
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Old 10-03-2019, 05:27 PM   #4
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Swapping out my stock thermostat to one with a digital readout was one of the first things I did.
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Old 10-03-2019, 06:04 PM   #5
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Was the prior thermostat both for AC and heat? Or just heat? If both, you should be able to make it work. Or do you have to use controls on the AC unit heat in the ceiling to adjust your AC?
No, the prior thermostat was for heat only -- the AC unit is manual with controls only on the roof mounted unit (...one rotary control for selecting fan or AC and the other for temperature control). The AC unit does not have a "heat strip", incidentally. I'm wondering if there's a way to wire the digital thermostat to the temperature control on the AC? Of course, the on-unit selector will still control on-off & fan will run continuously when on but the digital t'stat would more precisely control the temperature via compressor on/off. I guess my concern would be that I might somehow screw up the compressor...maybe mess with the built in cycle delay? Dometic actually sells a complete conversion kit for controlling both the AC (& furnace) from an included digital wall t'stat, but I'm enough of a DIY'er (and, "fiscally conservative") that I'd like to make current equipment function acceptably if practical.
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Old 10-12-2019, 01:30 PM   #6
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Update...and, another question

...just returned from camping trip to NC Mtns -- used the furnace one cool morning and the thermostat worked, flawlessly! That said, I now have in hand a Dometic "kit" to add a thermostat (will replace the one I just installed ) and this one will control both the AC and the furnace. My next issue is how to get a few wires to the roof air/inside ceiling opening? No doubt it will become clearer when I've removed the lower inside cover, but I'm wondering if there will be a way to "fish" wire over to/from the thermostat mount. Also, I need to route 12V supply wire from the converter to the ceiling opening -- that, too, oughta be "fun". It'd be nice to discover that the factory put wiring in place "just in case", but I don't expect that. Again, this is a '14 Apex 22QBS that came with manual controlled AC & I'm just wondering if anyone out there may have experience in pulling wire through the ceiling/walls?
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Old 10-12-2019, 04:27 PM   #7
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Upgrade suburban furnace thermostat(?)

Donít know your model but if you canít fish new lines you might consider WireMold products. You can get it in metal or several different dimensions of plastic. Loweís, HD and Menards should carry it.

https://images.app.goo.gl/Lt8UNQghKCKvtkD77
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Old 10-12-2019, 07:49 PM   #8
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Donít know your model but if you canít fish new lines you might consider WireMold products. You can get it in metal or several different dimensions of plastic. Loweís, HD and Menards should carry it.

https://images.app.goo.gl/Lt8UNQghKCKvtkD77
Thanks...I've been looking at those at Lowes as a possibility. There are already in place some ceiling seem moldings, so something that's "aesthetically" compatible may be the answer. I sure hope that there's a way to totally fish & hide the wires...but, it may be impossible. I'll get into it next week & report back.
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Old 10-12-2019, 08:31 PM   #9
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Depending on how many wires you need to pull, it will probably be easier to get them in a single cable (a outer sheath around X number of inner conductor wires). I would go with plenum rated cable if you can find what you need (rated to be run inside heat/ac ducts). Plenum rated is more flame and heat resistant that non-plenum cable and the roof can get warm even if insulated. One pull and done with a bundled cable.
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Old 10-12-2019, 09:01 PM   #10
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"plenum rated"

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Originally Posted by dward51 View Post
Depending on how many wires you need to pull, it will probably be easier to get them in a single cable (a outer sheath around X number of inner conductor wires). I would go with plenum rated cable if you can find what you need (rated to be run inside heat/ac ducts). Plenum rated is more flame and heat resistant that non-plenum cable and the roof can get warm even if insulated. One pull and done with a bundled cable.
Thanks -- did not know about this special cable. I'll have a two conductor running from the converter & thermostat wire 'twixt the ceiling unit & T'stat wall mount. It'll be great if I can fish and pull...but, if not, this sounds like the cable to utilize no matter which way I have to go.
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Old 10-14-2019, 08:12 PM   #11
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Question The project continues

With a little (...well, actually, a lot! ) work, the thermostat wire & new thermostat are in place and totally "hidden" in wall/in ceiling. Yay!! Now, to install the new control "box" in the ceiling unit. Directions specify a "dedicated" 12V supply from the converter (or, battery) to the ceiling unit -- to say that it would be a challenge to route this would be an understatement. Soooo...I'm wondering...since the OEM wiring anticipated incandescent lighting and we're utilizing 100% LEDs might the lighting circuit also support the amperage pull of the new thermostat and AC/furnace control(?) (That wire runs right through the ceiling AC unit). While I don't find the amperage requirements with the kit, the LCD thermostat won't pull much...most will be the relay(s) that will be controlling the AC fan, compressor and furnace on/off. If I haven't already totally confused all and if there's an electrical guru handy out there, I'd sure appreciate some related counsel. And, again, I do appreciate the ideas and observations already shared!
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Old 10-15-2019, 12:13 PM   #12
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Tapping into a light circuit to power the A/C controls will be fine. As you said above all you'll be controlling is the thermostat ( a few milliamps) and a couple of relays (maybe three). Automotive relay coils draw about 100ma, so you're talking about less than an amp there if they're all pulled in. If they're electronic relays they draw less than that.
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Old 10-15-2019, 07:17 PM   #13
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Talking Dometic manual to t'sat upgrade...done!

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Tapping into a light circuit to power the A/C controls will be fine. As you said above all you'll be controlling is the thermostat ( a few milliamps) and a couple of relays (maybe three). Automotive relay coils draw about 100ma, so you're talking about less than an amp there if they're all pulled in. If they're electronic relays they draw less than that.
Thank you, Bama Rambler!! Got it all installed and tested today & it works as advertised...and, utilizing the available 12V power @ the ceiling unit made an almost impossible "wiring job" a breeze. As a long time DIY'er with some experience in both auto and aircraft maintenance it just "made sense" to me that the lighting circuit would be more than sufficient. Your assurance gave me the confidence to complete the "job", safely. The only thing remaining is to cover the "unfiltered" air holes left from removed manual knobs. In the total realm of things, having a T'stat to accurately control both AC & furnace probably isn't a big deal, but I sure do like it and think it adds to the experience (and value). Thanks, again, Rambler and all who have shared thoughts & experience!
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Old 10-16-2019, 10:08 AM   #14
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Thank you, Bama Rambler!! Got it all installed and tested today & it works as advertised...and, utilizing the available 12V power @ the ceiling unit made an almost impossible "wiring job" a breeze...

<snip>

The only thing remaining is to cover the "unfiltered" air holes left from removed manual knobs.
You're welcome. I'm glad it worked out and that there was power in easy reach.

You could... just buy a new ADB (Air Distribution Box) (aka, Non-ducted ceiling assembly) that doesn't have the holes!
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Old 10-16-2019, 06:12 PM   #15
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ADB...

Bama Rambler wrote: "...... just buy a new ADB (Air Distribution Box) (aka, Non-ducted ceiling assembly) that doesn't have the holes!"

Now, there's another great idea! If I can fabricate an acceptable "cover" (...acceptable to wife ) it'll be a bit cheaper than new ADB...but, that's gonna remain as an option.
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