Help with Strange Suburban Furnace Issue

[Calbar]

First, I hate throwing parts at an issue, it wastes my time and money (If I install something and it doesn’t fix the problem it
come out of my pocket) and irritates the owner who just
wants the problem resolved.

I think there are a few options depending upon abilities.

1. Take the unit to a dealer and deal with the usual issues of dropping the unit off, going back to pick the unit up, and maybe not having the problem fixed. Warranty service is far from free when factoring in the cost of making two trips to drop off and retrieve the RV.

2. Replace the control board or motor yourself. The control board depending upon the source is under $150, motor typically also under $150. My first choice is the board. Why? Experience, boards fail frequently, motors much less often.

3. Suburban sells what they call a furnace core - the complete furnace minus the sheet metal surrounding the furnace. Often times these can be found for under $500.

A caveat about purchasing a furnace core - furnaces come with the gas line connection at either the front or back of the furnace. The kicker is the front isn’t where I think it is. The front in suburban terminology is the back to me. To Suburban the back is the area where the motor and the outside access panel is located. If your furnace is typical to Grand Design with the gas connection near the outside wall of the RV you need a rear/back
connection

BTW - I’m still thinking control board.

Thanks Colan,

I appreciate the feedback. I currently have sent the dealer the information and waiting to hear back. I agree with you that it costs me just to drop it off. Not a short drive. I currently have some other issues that they need to fix as well so it make sense to me to take it back. I am very handy and will do nearly all repairs myself once the warranty is done and will keep tabs on this one for sure.

Rob

[Scott'n'Wendy]

colan The reason I said 'they will replace' the furnace is because I noticed he has a 2022. If the furnace is going wonky, I'm pretty sure he will make use of the warranty. Otherwise I agree with you, take it out and determine the culprit rather than just throw parts at it until you fix it by luck.
I also agree with your 'boards fail more often than motors' sentiment. The reason I'm saying bearings is because I can't see a way for the main board to fail in such a way as to vary the motor speed.Not starting, not stopping, intermittent stopping, random stopping I can see being the board. Boards also don't make noises, they are a silent killer to RV fun.
This is why I like trying to help diagnose problems on forums. You have to do all the troubleshooting in your head and logically try to determine the problem..and you get to see other peoples thought process. Which helps me improve my thought process. Sometimes we are trying with only half the relevant information..lol

[howson]

colan -- do you recommend and install Dinosaur boards or replace with OEM?

[Guest]

Does the board control speed or torque or just operate a relay to provide battery power the the blower motor? I'm thinking the later but can a relay fail in a way to reduce current to the motor? I'm wondering if the motor is failing once it heats up.

If its possible to check pressure drop across the blower and to monitor current the next place to look would be the motor and bearings. Generally a bad bearing once hot, can cause a wobble of the fan and a rumble noise where the result would be reduced RPM (pressure) of the blower.

If current drops off then the issue could be a board.

Jim

[Scott'n'Wendy]

Does the board control speed or torque or just operate a relay to provide battery power the the blower motor? I'm thinking the later but can a relay fail in a way to reduce current to the motor? I'm wondering if the motor is failing once it heats up.

I could give you examples of that in higher voltage 3 phase applications but have not seen it in 12vdc

[colan]

When the board is covered by warranty I replace with a board from the furnace manufacturer. When the furnace is out of warranty typically I use Dinosaur boards.

Why use factory boards when it is a warranty repair? It is a manufacturer requirement.

colan -- do you recommend and install Dinosaur boards or replace with OEM?

[Calbar]

Well just got back from the dealer and the furnace motor was bad. After they ran the furnace for 1/2 hour the tech had it start to do the same thing that we have experienced. Replaced the motor and ran for some time again and all was good.

Glad the problem didn't vanish and that it is now fixed.

Rob

[Scott'n'Wendy]

Calbar
Always good to hear a story of someone going to the dealer service department and having something diagnosed properly and satisfactorily repaired. You usually only hear the horror stories..lol