Need a rooftop a/c guru

Scott & Heather · July 06, 2016, 07:48:03 AM

We purchased and Atwood air command rooftop air conditioner. It is one of the units that is controlled by a wall thermostat. Atwood has a digital wall thermostat, but we would like to use a house style thermostat. I would like this thermostat to Control both the furnace and the air-conditioner. I have not been able to get it to work even though I have connected the wires properly. When I called Atwood the gentleman I spoke to basically said it couldn't be done. He was very rude, and he did not want to hear any other options other than buying their Atwood thermostat. So I'm reaching out to the form for help. Is there a way that I can make a house thermostat work. Do I need to run 12 V to the air-conditioner?

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thomasinnv · July 06, 2016, 08:31:14 AM

Scott there should be a control board inside the ac unit and yes you need to run 12v to it. If memory serves correctly, the thermostat wires from the furnace go to the control board, and the wall thermostat also connects to the control board. There are different versions of the control board and you need to have the right configuration to do what you are looking for.

TomC · July 06, 2016, 08:38:25 AM

Furnace control is just a simple on off affair. A/C control with thermostat needs 12v. Most household thermostats and A/C controls work with 24v ac, not the 12v dc that your unit works with. Just bite the bullet and use their thermostat. Good Luck, TomC

brmax · July 06, 2016, 09:10:36 AM

plus 1 with what Tom mentioned
Brian without seeing a schematic for the model its going to be tough on us nuts.
no offense : )
In many units like your pic the 24v has been the trigger voltage for a long time opening the hi-voltage contacts through a coil or the likes, so one has to know the units need and its clarity you could say. To bump that nowadays some of the circuit boards are even using some new voltage "biased" stuff.
I am! curious as this has little to the operation, what I would think the board may have is a time delay on restarts. But without sensor wires from the unit showing these signal loads the board would just use the hokie method after a power out.

will keep an eye for any tips
good luck
Floyd

Stormcloud · July 06, 2016, 12:23:58 PM

I installed a residential thermostat to control the gas furnace and the roof-mounted air conditioner in our 5th wheel trailer.
It has been a while since I did this, but I think this link should give you some insight.
Yes, it can be done.

http://rvroadtrip.us/library/digital_thermostat.php

Mark

bigred · July 06, 2016, 06:02:51 PM

I just this went through this deal with putting new AC'S on my Prevost.Camping World used a 120x12v adapters on mine .Was only like 59.00 .I could not believe the crock of manure I had to go through for 3 AC'S.

digesterman · July 06, 2016, 06:30:20 PM

It can be done, first one is a little tricky but the rest are easier. I put all wifi controlled in mine and love them, can turn them on and off, adjust and see temp anytime and anywhere I happen to be. Only way to go

Edited to add that I have 4 basement units. The Honeywells require 24v but you can buy 12 to 24v transformers

Scott & Heather · July 06, 2016, 08:55:06 PM

Ok, so I am at a loss here. When the ac unit it energized, I get like 5 volts to two of the small wires (out of the four) in the thermostat wire harness. Seems to me that they've designed this to use their proprietary thermostat? Argh.

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scanzel · July 07, 2016, 04:08:30 AM

Be care full if you burn up the control board in the air conditioner the thermostat won't be your only problem or expense plus you could void any warranty if the unit is new. My central thermostat for my Penguins requires 12v dc and two telephone 4 conductor cords to interconnect everything together.

thomasinnv · July 07, 2016, 06:53:45 AM

Yes scanzel is on to something. The older ac control boards can be used with a variety of thermostats as they are basically a series of relays (kind of but not really) and all they need is open or close contact to operate the various functions. The newer control boards utilise a network protocol of sorts to communicate with each other and you have to use a proprietary thermostat. If you are electrically savvy you could rewire with older style control boards and use older style thermostats, but for the cost and the trouble its really not worth it in my opinion.

luvrbus · July 07, 2016, 07:53:35 AM

I don't have any idea how the they do it but the upper end conversions like a Marathon Prevost or Newell they control all 5 units through the Crestron system,that would be a little expensive,I do like the idea that the fan motor has a 1 minute delay and stops after the compressor stops when the temp setting has been reached

brmax · July 07, 2016, 08:54:19 AM

Your on to something now Scott
As we were talking about a little earlier some of the hi volt contacts still use the base of systems with low volts like 24 to the coils.
With the pc stuff from the 80's the boards typically use a 5volt reference to signal. So there may well be a basic board system in the unit now, I don't have a clue to help but wished I did, sorry
have a good day with the task
Floyd

Geoff · July 07, 2016, 10:28:39 AM

Years ago this subject came up and it was revealed that WalMart sold an inexpensive wall thermostat that would work in an RV. I use Colman wall thermostats that have both heating and cooling adjustments.

--Geoff

Seangie · July 07, 2016, 08:07:53 PM

Quote from: Scott Bennett on July 06, 2016, 08:55:06 PM
Ok, so I am at a loss here. When the ac unit it energized, I get like 5 volts to two of the small wires (out of the four) in the thermostat wire harness. Seems to me that they've designed this to use their proprietary thermostat? Argh.

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Scott,

Where are you getting your +12, +24v from?

It should be coming from the coach.

A couple things here (Nick tell me if Im off base here)

1. Make sure your thermostat can work with a DC voltage. As Tom said earlier it might need a low voltage AC signal instead of a DC signal.

2. Once you figure out what voltage the thermostat can work with then feed the thermostat with that voltage. So if it works with 12v DC then grab a positive and negative 12v wire from your batts and power up the thermostat. If its not 12v dc then provide whatever voltage the thermostat needs.

3. With just the positive and negative hooked up to the thermostat (it may also ask for a ground as well to work properly. Just run a wire to your bus frame) click the thermostat on in such a way that the Air conditioning would power up. Check the voltage of the lead wire thats supposed to go to the Air Conditioner. Check that voltage. That voltage needs to match what the control board on the AC unit requires to power on. For example - My coleman Mach 8 control board (and for the mach 8 its a seperate board that doesnt come with the unit. You have to buy the control board and plug it into the roof unit to work with a thermostat) uses a 12v signal. In my case if the thermostat does not put out a 12v signal then the roof air wont turn on.

4. If the thermostat does not put out the correct voltage then you will need the correct piece of electronics to change that signal from the voltage that the thermostat puts out to the voltage the roof air needs. Ie 24v DC to 12v DC.

Id upload a diagram but Im in Canada until next week and network is spotty plus Im on vacation. And there is a cold beer in the fridge waiting for me....

Haha. Just call me at 5am tomorrow and Ill talk you through it.

-Sean

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Scott & Heather · July 07, 2016, 08:18:38 PM

Lol thanks Sean! Sorry for waking you up the other day. Atwood kindly is sending me their proprietary thermostat free of charge asap. Like it shipped today from Indiana. Very nice of them. Surprised me actually. Once I get it and get the ac operating, I'll experiment more with it. Right now I just don't have the time. We did get power today finally

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