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Older Atwood 8531-III furnace (1996!)......New motor now,

Older Atwood 8531-III furnace...

Older Atwood 8531-III furnace (1996!)......New motor now, other one squealed like a pig. Re connected all the wires like they were previously, I took lots of pics! Old T stat was shot, replaced with a new analog from Amazon, wired it according to diagram.....no joy! "tricked" the furnace with a jumper on both blue wires.....came on and worked great. Got a Digital T stat, wired that according to diagram / info from the net. NOTHING again.........retricked furnace........came on fine. My question is.....does the digital T stat have enough voltage from it to engage the time delay switch. And should that be connected to the blue wire on the time delay switch????? Any info would be great!!!!

Mechanic's Assistant: The RV Mechanic can find the right wiring diagram for you. Would you like any additional help or materials?

Yes please.

Mechanic's Assistant: Is there anything else the RV Mechanic should know before I connect you? Rest assured that they'll be able to help you.

I did replace the old motor, and checked it via 12 volt source prior to reconnecting all thewires.

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Answered in 16 minutes by:
4/27/2021
RV Mechanic: KevinS121,
 replied 1 year ago
KevinS121
Category: RV
Satisfied Customers: 2,550
Experience: Expert
Verified

Howdy and welcome to Just Answer.  My name is ***** ***** and I am a Master Certified RV Tech. I understand how frustrating RV issues can be.  I have been  working on RVs for 35 plus years.  I see you are having an issue with the furnace and wall thermostat.  Give me a few minutes to do some research and I will be right back.  If you can give me a wire diagram of your thermostat, I will pull one up on the furnace and try and match things with you.

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Customer reply replied 1 year ago
Hi Kevin! The T stat is a Honeywell Home RTH221B1039 RTH221B it did not come with a wiring diagram for an RV. The info I found that was working for virtually everyone else ( sarcasm tone) has the fan Hi and Low into the "G"spot....Yellow / AC in the "Y", White for furnace / heat in the "W" spot and the Ground in the "R" spot. I can jump the blue wires and it will work.....hence my frustration!!! I'm wondering if the relay isn't seeing voltage or even enough!Or....maybe the relay is bad! Of course I'm not near my RV to go check today!Does that relay require constant voltage in order to keep the furnace operating? Does the digital t stat just send a pulse???
RV Mechanic: KevinS121,
 replied 1 year ago

try swapping the 2 blue wires on the thermostat.

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Customer reply replied 1 year ago
Planned on doing that very thing tomorrow!!! Thoughts on the digital T stat not supplying enough voltage???Planned to do that tomorrow....once I have it here!
Thoughts on the digital t stat not have enough voltage to maintain function or even start the furnace?
RV Mechanic: KevinS121,
 replied 1 year ago

The thermostat is going to get the voltage from the furnace.  that is why it will not work.  one of the blue wires feed the 12v to the furnace.  the other one is wired to ignitor board, sail switch and limit switch.

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Customer reply replied 1 year ago
the digital one wont work because no voltage flow?
RV Mechanic: KevinS121,
 replied 1 year ago

this thermostat will not work in your RV.  This thermostat is designed for ACV, you are dealing with 12vdc

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Customer reply replied 1 year ago
CopyDamn it.....LOL
RV Mechanic: KevinS121,
 replied 1 year ago

Are you trying to control your A/C and furnace or just the furnace?

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Customer reply replied 1 year ago
Ok...
I also have a Dometic(###) ###-####032 analog t stat.....I'll put it back in.....but it wasn't starting the furnace either......worked fine with the AC unitBasically that white wire must send 12v down to the relay to start the furnace....correct?The AC worked fine with both t stats digital and analogJust no joy with furnace!
RV Mechanic: KevinS121,
 replied 1 year ago

Here is the wiring diagram for that thermostat.  It gets it power from the A/C control box.  There is only one wire going to the furnace.  what you will need to do, is go to the wiring on the furnace and tie one of the blue wires to the positive wire on the furnace.  That would be the red wire.  then the other wire goes to the thermostat. https://images.search.yahoo.com/search/images?p=dometic+3106995.032+analog+t+stat+wiring+diagram&fr=mcafee&type=*****************4&imgurl=https%3A%2F%2Fwiringdraw.co%2Fwp-content%2Fuploads%2F2019%2F01%2Funique-wiring-diagram-for-duo-therm-thermostat-learning-as-well-dometic-digital-diagra-revistasebo-com.jpg#id=0&iurl=https%3A%2F%2Fwww.rvpartscountry.com%2Fassets%2Fimages%2Finstructiontstat.jpg&action=click

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Customer reply replied 1 year ago
Copy , I'll give that a try in the am! Thank you very much!!
RV Mechanic: KevinS121,
 replied 1 year ago

My pleasure.  Glad I could help. I appreciate good ratings for my service today.   If you are not satisfied with my service today, please let me know so I can do better next time. There are also other experts available to help you as well.   Thanks for using Just Answer and have a great day.

Happy RVing

***** *****

Customer/p>

If you will notice, the power going to the thermostat is only 7.5 vdc.  The ceiling control box drops the voltage down for that power wire.

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Customer reply replied 1 year ago
Excellent! I will definitely check that!
Will there be 7.5 or 12 v at the relay???
RV Mechanic: KevinS121,
 replied 1 year ago

on the furnace is 12v

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Customer reply replied 1 year ago
Thanks again for your help!
RV Mechanic: KevinS121,
 replied 1 year ago

Let me find the wiring diagram for the furnace so you will understand how it is wired and which blue wire to connect to the red wire.

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Customer reply replied 1 year ago
Copy! You are THE man!!
RV Mechanic: KevinS121,
 replied 1 year ago

follow this diagram for hooking up the furnace with that thermostat.

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Customer reply replied 1 year ago
Hi Kevin....***** ***** here....I checked all the wires up stream of the furnace. All are good.
The red and white wires from the blue wires on the furnace are fine. The red is 12.6 volts....the white is ground.
I can hook those to together at the t stat location....the furnace comes on!
I tried hooking up the Dometic analog stat.....no go! AC works fine with fan hi and lo function.
I'm at a loss, ready to drink.I did check all the connections on the furnace as well....all are good....only thing is on the relay I have voltage before the switch but not after.
I can trick the unit with the blue wires and it comes on and begins heating.You think maybe that relay is bad?.....but the unit works when jump with the blue wires!I'm really confused!Any thoughts
RV Mechanic: KevinS121,
 replied 1 year ago

change the 2 blue wires.  if you notice, one blue wire is connected to the red wire on the furnace.  the other blue wire goes to the thermostat.

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Customer reply replied 1 year ago
One of the blue is to the red, the other blue to the white.The red and white run up to the stat.There is 12 volts there......I can hook them together and run the furnace. Oddly enough!I'm going to get my RV in about an hour.I have the old stat....with the broken slider and going to hook it up just to see if it does anything via the switch.I'll take pictures of all the stats and the connections.
As well as the volt meter hooked up!
RV Mechanic: KevinS121,
 replied 1 year ago

From the furnace, you will have only one wire going to the thermostat, that is the  Blue that has no power.  Red does not go to thermostat, white does not go to thermostat.  Red is power from the power center.  white is ground.

you are dealing with the wires that are circled, nothing else.

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