larry cad
ohio
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Joined: 05/23/2004
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dougrainer wrote:Dusty R wrote:That switch should never need to open. If it does there is not enough air moving through/over the furnace.
They open and close all the time. OEM furnace ductwork installs NEVER match the correct volume of air required to run the furnace without the Limit occasionally tripping. Also the RV'er will block off some floor ducts to get more heat or air to some areas of the RV. That will also cause the Limit system to trip. YES, it would be nice if the Ductwork was installed to meet the Minimum requirements to prevent Limit switch tripping. I can ALWAYS make both Furnace and Roof AC ductwork many times more efficient, but unless under warranty, the customer will not want to pay for a check out and making it to best operation. Rarely do I get a complaint about Ductwork under warranty. They just figure that is the way it is. Doug
Great information. Thanks Doug
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dougrainer
Carrolton, Texas
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Zero(0) IS the smallest square bit. I was thinking of the No 1 that is used on some Canadian built door cabinet latches. Doug
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Boundless2281
PA
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Joined: 02/25/2023
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Hello,
I know this is an old post, but I have the exact same furnace and need to bench test it. I am unsure what to do with the blue thermostat wires. I applied 12V to the positive and negative wires, but I am not sure what to do with the 2 thermostat wires. Do I need to connect them together? Or do they get supplied with 12V? They are both blue, does the polarity matter if I am supposed to be connecting them to 12V??
Thank you.
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trailrider
Idaho Is Full! Don't Move Here!!!
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Connect the blue wires together to run the furnace.
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Boundless2281
PA
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Okay thank you. That's what I was afraid of. I did that and nothing happened. Verified 13+ volts to the positive and negative lead. No noise or anything from the furnace. I am going to check all the connections, but it seems like I may be buying a dinosaur board to replace mine.
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JBarca
Radnor, Ohio, USA
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Joined: 12/16/2004
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Boundless2281 wrote:Okay thank you. That's what I was afraid of. I did that and nothing happened. Verified 13+ volts to the positive and negative lead. No noise or anything from the furnace. I am going to check all the connections, but it seems like I may be buying a dinosaur board to replace mine.
Atwood had several control vintages of this furnace, the prior version used a thermal timing relay to run the fan and fan delay. The PC board, in this case only ran the gas valve, ignition, and flame sense circuit.
The next generation of controls did away with the timing relay and added the fan control to the PC board, which then controlled that fan and the gas valve, ignition, and flame sense.
Does your furnace have the thermal timing relay?
See the timing relay here; it is on the right end of the blower housing.
![[image]](https://live.staticflickr.com/65535/49022085107_a06840eb6a_o.jpg)
Here is the newer vintage with the fan control on the PC board—no thermal timing relay. A PC wire plug is on the front of the PC board; a blue wire, the T stat run signal, was added and is part of the fan control. The T stat run signal on the older thermal timing relay received the T stat signal.
![[image]](https://live.staticflickr.com/4695/39690690611_652195ac8d_o.jpg)
![[image]](https://live.staticflickr.com/4723/39690695511_f3e752d7c6_o.jpg)
![[image]](https://live.staticflickr.com/4694/39690694311_f5d977d08e_o.jpg)
This PC board has fan control on it. The black relay on the PC board in this pic is for the fan motor (the red wire is the fan motor hot wire, and the blue next to it is incoming 12-volt power for the fan motor). The round coil igniter also has a red wire but different insulation and goes to the electrode.
Some checks, and this assumes you have a 12.5 DC power or higher coming to the furnace.
If yours has the timing relay, they have been known to go bad over time. If you connect the two blue wires within a short period, the blower should run; if the blower will not run, either the motor is bad (less likely) or the thermal timing relay is bad (more likely). Check the fan power wires and see if it is getting power; if there is no power, then the relay is bad.
If you have no timing relay and twist the two blue wires, the fan should run after a few seconds as the PC board controls the fan motor. Check the fan motor power wire coming out of the PC board to see if the board is sending incoming DC voltage to the motor. If the board is sending power, then the motor has issues. If the board is not sending voltage, the board has issues.
Hope this helps
John
* This post was
edited 02/26/23 05:46am by JBarca *
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