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Old 01-23-2021, 11:56 AM   #1
jasongind
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Analog to Digital Thermostat Help

Hello all,

We have a 2021 Keystone Hideout 176LHS. It has a Suburban furnace controlled with a Suburban analog thermostat (two wire, one white and one red). The AC is a Coleman Mach ceiling unit with controls on it.

I did search and couldn't find my answer. I'm trying to replace the old analog Suburban thermostat with the Coleman Mach 8330-336 digital thermostat. I ran new wires to connect the Airxcel unit to the thermostat. All connections were made with spade connections and are pushed firmly onto the male connector on the Airxcel unit.

I replaced the ac ceiling unit controls with the Airxcel control unit. I have it all connected but I'm not able to control the AC or furnace with the thermostat.

Here is how I wired so far:

Thermostat wires:
white to furnace white
Red to furnace red
Blue to -B terminal
Yellow to Y terminal
Green to Fan Low terminal
Grey to Fan High terminal

With the red to red the LED display works and I can hear it clicking trying to turn on but nothing turns on. If I connect the thermostat blue to the furnace red I have no LED display and the furnace kicks on and runs continuously.

I've been messing with this thing for a weeks on and off.

Anyone have any suggestions?
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Old 01-23-2021, 02:48 PM   #2
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Originally Posted by jasongind View Post
Hello all,

We have a 2021 Keystone Hideout 176LHS. It has a Suburban furnace controlled with a Suburban analog thermostat (two wire, one white and one red). The AC is a Coleman Mach ceiling unit with controls on it.

I did search and couldn't find my answer. I'm trying to replace the old analog Suburban thermostat with the Coleman Mach 8330-336 digital thermostat. I ran new wires to connect the Airxcel unit to the thermostat. All connections were made with spade connections and are pushed firmly onto the male connector on the Airxcel unit.

I replaced the ac ceiling unit controls with the Airxcel control unit. I have it all connected but I'm not able to control the AC or furnace with the thermostat.

Here is how I wired so far:

Thermostat wires:
white to furnace white
Red to furnace red
Blue to -B terminal
Yellow to Y terminal
Green to Fan Low terminal
Grey to Fan High terminal

With the red to red the LED display works and I can hear it clicking trying to turn on but nothing turns on. If I connect the thermostat blue to the furnace red I have no LED display and the furnace kicks on and runs continuously.

I've been messing with this thing for a weeks on and off.

Anyone have any suggestions?
It sounds like you blew the low voltage fuse when you hooked up blue to red. Check with chuckS. Or one of the otherrv guys on here, chuckster57,jrtjh I believe with the fuse blown the fan will run continually
Make sure your battery is charged and the wires on thermostat actually match the wire connections on furnace also ie blue to blue white to white etc. Also it looked like green is fan hi and gray is low
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Old 01-23-2021, 03:04 PM   #3
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It sounds like you blew the low voltage fuse when you hooked up blue to red. Check with @chuckS. Or one of the otherrv guys on here. I believe with the fuse blown the fan will run continually
Make sure your battery is charged and the wires on thermostat actually match the wire connections on furnace also ie blue to blue white to white etc. Also it looked like green is fan hi and gray is low
Your right on the fan speed. I verified and I have them hooked up correctly, I just transposed them when typing the op.

I did a resistance test and the low voltage fuse is still testing as good. The only two original wires I have are the white and red coming from the Suburban furnace. I had to run wires from the new Airxcel contril unit to the thermostat. They are all labeled correctly and going to their corresponding locations on the thermostat ie. Y to Y, -B to Blue, GL to Grey and GH to Green. Then the original furnace white to thermostat white and original furnace red to thermostat red.
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Old 01-23-2021, 03:13 PM   #4
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Your right on the fan speed. I verified and I have them hooked up correctly, I just transposed them when typing the op.

I did a resistance test and the low voltage fuse is still testing as good. The only two original wires I have are the white and red coming from the Suburban furnace. I had to run wires from the new Airxcel contril unit to the thermostat. They are all labeled correctly and going to their corresponding locations on the thermostat ie. Y to Y, -B to Blue, GL to Grey and GH to Green. Then the original furnace white to thermostat white and original furnace red to thermostat red.
There are a few guys on here that have rv furnace experience. They are different ( control wise ) to furnaces I work on. Someone will chime in soon. Just keep an eye out for an email saying someone replied or just monitor this thread a while today
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Old 01-23-2021, 03:25 PM   #5
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I think if it were me I would try and wire just the furnace first. I would disconnect the ac unit and look at the wiring to furnace only. You may have to pick up 12v - from the furnace. And not the ac so I'm thinking look at the schematic and see what you would need to power the thermostat. I would imagine it would be red white and common (12-)
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Old 01-23-2021, 03:27 PM   #6
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I think if it were me I would try and wire just the furnace first. I would disconnect the ac unit and look at the wiring to furnace only. You may have to pick up 12v - from the furnace. And not the ac
I thought about that but there is no -12v coming off the furnace to the thermostat, just the white and red. I guess I can find the furnace -12v wire and tap into it, run it to the thermostat and see what happens.
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Old 01-23-2021, 03:29 PM   #7
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I thought about that but there is no -12v coming off the furnace to the thermostat, just the white and red. I guess I can find the furnace -12v wire and tap into it, run it to the thermostat and see what happens.
Is this your furnace?
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Old 01-23-2021, 03:53 PM   #8
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Is this your furnace?
No mine is the NT-20SEQ. I just found the schimatic and it says the yellow wire is -12v. I run a jumper from it to the thermostat blue (-12v) wire and the furnace is working now.

Any idea where I now hook up the ac -B to complete that circuit?
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Old 01-23-2021, 04:10 PM   #9
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No mine is the NT-20SEQ. I just found the schimatic and it says the yellow wire is -12v. I run a jumper from it to the thermostat blue (-12v) wire and the furnace is working now.

Any idea where I now hook up the ac -B to complete that circuit?
I sent for reinforcements. Will see if they can come if not someone will be able to help
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Old 01-23-2021, 04:30 PM   #10
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If this were a residential furnace I could be more helpful. I've learned in the last few days that there are inherent differences between RV furnaces and what I normally work on. Forum member ChuckS has more knowledge on RV furnaces. He may be able to weigh in on the subject..sorry I couldn't be of more help.
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Old 01-23-2021, 04:39 PM   #11
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If this were a residential furnace I could be more helpful. I've learned in the last few days that there are inherent differences between RV furnaces and what I normally work on. Forum member ChuckS has more knowledge on RV furnaces. He may be able to weigh in on the subject..sorry I couldn't be of more help.
Oh no man you've been a help. Just havi g this conversation allowed me to thibk about it from a different point of view and got the furnace working. Much appreciated 👍

Now I'll find the schematic for the ac unit and find somewhere to connect the -B terminal too.
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Old 01-23-2021, 04:56 PM   #12
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Oh no man you've been a help. Just havi g this conversation allowed me to thibk about it from a different point of view and got the furnace working. Much appreciated 👍

Now I'll find the schematic for the ac unit and find somewhere to connect the -B terminal too.
Your welcome and good luck
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Old 01-23-2021, 05:23 PM   #13
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Oh no man you've been a help. Just havi g this conversation allowed me to thibk about it from a different point of view and got the furnace working. Much appreciated 👍

Now I'll find the schematic for the ac unit and find somewhere to connect the -B terminal too.
One more thing. I looked up the airexcell control box conversion and it says to get 12 v dc from converter or battery directly to avoid any control issues

It looks to me like you power the thermostat from the furnace... Both the ac and the furnace share a common ground b-
When the thermoset calls or heat it R (12+ ) to w to bring on furnace
R to green or gray brings on fan only up in the ac unit ( the b- is always present to provide 12 volts for relays after r sends power to y( compressor) or the high and low fan.
I think you may be able to tie all your b- wires together and then yellow green and gray to ac with the common b- as well. I'd have to look at the schematic for the heat because it's just blue wires I believe for a 2 wire system. I haven't had to ever site one up. So not sure on that right now.
Be careful you do not bypass any safety switches if you are guessing which wires. ( hi limit or other)
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Old 01-23-2021, 05:31 PM   #14
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Ok, finally have a minute;

Furnace will have 4 wires, and the two blue are the thermostat. One will be “hot” and that’s the one that needs to be hooked to the + side of the thermostat.
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Old 01-23-2021, 05:32 PM   #15
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It looks like the two blue wires that originally went to your stat are now going to be different now...Use red for 12+ it and one of the blue wires go to same terminal it looks like.
Use yellow for 12- and the blue that goes to the valve switch for w...( red and blue are the same on one side)
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Old 01-23-2021, 05:34 PM   #16
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Yellow at the thermostat is used for AC signal at the control box.
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Old 01-23-2021, 05:36 PM   #17
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Yellow at the thermostat is used for AC signal at the control box.
Yes and the b- should come from the converter or battery or is it ok to pull from b- at furnace?
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Old 01-23-2021, 05:37 PM   #18
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Yellow at the thermostat is used for AC signal at the control box.
And the other blue wire that goes to valve switch would be W? That's what I see
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Old 01-23-2021, 05:40 PM   #19
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Yes and the b- should come from the converter or battery or is it ok to pull from b- at furnace?
When we add a second ac unit there is usually 12V there, so maybe you could pull from a lighting circuit at the control box. ALL grounds both AC and DC are tied together at the frame.
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Old 01-23-2021, 05:42 PM   #20
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And the other blue wire that goes to valve switch would be W? That's what I see
Without having the furnace in front of me, sounds right, but probably AFTER the sail and overlimit switches, I usually look at the schematic provided on the furnace itself.
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