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  • Help with Strange Suburban Furnace Issue

    I have a strange Suburban Furnace issue with intermittent air flow and strange noises. It runs fine most of the time especially when keeping the trailer at temperature but once on the last trip and several times arriving here in Ottawa it does this.
    1. Will run fine for at least 1/2 hour or more. Ran fine 45 minutes yesterday and this morning.
    2. Can hear the airflow slowing down and starts making strange sounds (almost a rumbling that slows and increases with speed)
    3. Airflow really slows down but increases and decrease up and down. Can hear the blower struggling as well.
    4. Finally stops.

    If I let it sit for a bit and turn off the thermostat and then turn it on 15 or 20 minutes or more later will run like normal again. Did this 3 times a couple of days ago when bringing up the trailer to temperature from about 8C (46F) to 22C (72F). Even from 19C (66F) it did it the last time.

    This is on shore power and the first time was on battery power. Initially I thought it was low battery but now I think it is bearings but it seems to run fine 95% of the time. If it was bearings I would think it would be an issue all of the time.

    It does also have a bit of a high pitched whine to it that I have not had in previous trailers before which I assume could be bearings.

    I have been timing it to see how long it runs before it happens but of course now it doesn't happen.

    Propane tank if full and all of the electrical is working fine and battery shows full charge.

    Any additional insight is much appreciated as I suspect the dealer will run it for 20 minute and say there is nothing wrong.

    Thanks,
    Rob​
    Rob & Barb
    2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
    2022 Solitude 378MBS

  • #2
    Calbar

    The issue could be related to either the air intake or exhaust paths. Let me try to explain my thinking.

    There are two air paths. One is for combustion and the other for the air that is circulated in the trailer. Inside the furnace are two distinct "squirrel cage" fan wheels with each one (obviously!) either moving combustion air or internal air. They are tied together on the same shaft and motor. If any of the intake or exhaust paths get blocked, creating resistance to air movement, all of the air paths will be affected.

    First place I'd look is the ducts where they are connected to the furnace. If one (or more) are somehow collapsing or there is some kind of blockage (that is intermittent) what I'm thinking is that with air pressure removed the collapsed duct (or blockage) "resets". 100% speculation on my part but it could explain the symptoms presented. (The reason the furnace stops is because it overheats due to the lack of air movement, so it automatically shuts down.)

    Could it be a bearing? I'm not a bearing expert by any stretch of the imagination, but won't there be a difference when the bearing gets hot (if there's an issue)? It's possible to change out a fan in a furnace, but due to labor costs (assuming you'll pay someone to do it) it may be more cost-effective to just replace the entire furnace if it is a bearing.

    One more thought: if you have a dealer or mobile tech look at the issue, they may state that the only way to do a full bench check is by removing the furnace from the trailer. They aren't wrong (unfortunately), thus there's going to be a stiff labor cost just to troubleshoot, so keep that in mind.

    Howard
    Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

    2017 Ford F-350 DRW, '19 315RLTSPlus

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    • #3
      Originally posted by howson View Post
      Calbar

      The issue could be related to either the air intake or exhaust paths. Let me try to explain my thinking.

      There are two air paths. One is for combustion and the other for the air that is circulated in the trailer. Inside the furnace are two distinct "squirrel cage" fan wheels with each one (obviously!) either moving combustion air or internal air. They are tied together on the same shaft and motor. If any of the intake or exhaust paths get blocked, creating resistance to air movement, all of the air paths will be affected.

      First place I'd look is the ducts where they are connected to the furnace. If one (or more) are somehow collapsing or there is some kind of blockage (that is intermittent) what I'm thinking is that with air pressure removed the collapsed duct (or blockage) "resets". 100% speculation on my part but it could explain the symptoms presented. (The reason the furnace stops is because it overheats due to the lack of air movement, so it automatically shuts down.)

      Could it be a bearing? I'm not a bearing expert by any stretch of the imagination, but won't there be a difference when the bearing gets hot (if there's an issue)? It's possible to change out a fan in a furnace, but due to labor costs (assuming you'll pay someone to do it) it may be more cost-effective to just replace the entire furnace if it is a bearing.

      One more thought: if you have a dealer or mobile tech look at the issue, they may state that the only way to do a full bench check is by removing the furnace from the trailer. They aren't wrong (unfortunately), thus there's going to be a stiff labor cost just to troubleshoot, so keep that in mind.

      Howard
      Thanks Howard,

      I will check the ducting. I have been in the basement once and all looked good and all cold air returns are un-ducted, under the stairs and under the den dresser. Trailer is still under warranty so not too concerned about labour at this point. Just don't want to be stuck with a flakie furnace once warranty is out and then if finally dies.

      I was thinking similar with bearings but I don't have experience there either.

      Rob
      Rob & Barb
      2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
      2022 Solitude 378MBS

      Comment


      • #4
        I think it is more likely you have a motor/blower bearing issue. If it was the air in/air out path, I don't think it would vary like you have said. Bad bearings can change behavior with heat....or cold... Just my 2 cents

        After verifying the air path, if it's fine, I think you will be taking it out and running the motor without LP connection to determine if it is motor or blower. It may be an assy though and you have to replace both.
        Last edited by Scott'n'Wendy; 10-09-2022, 10:21 AM.
        2018 Dodge 3500 6.7 Cummins w Aisin and 9 cup holders
        Not to brag or anything about my finances, but my bank calls me about every day to tell me my balance is OUTSTANDING!

        Comment


        • #5
          This issue can also be a control board with an intermittent problem. Was down that road on a couple of furnaces last winter.

          How can the control board have an effect upon the fan motor? 12v positive is wired to the control board, the control board is basically a bunch of on/off switches (relays) and timers. If fan motor relay is acting up there will be low or no voltage/current to the fan motor.
          Colan Arnold
          2016 Momentum 397TH
          Full time since 2016

          Comment


          • #6
            Originally posted by colan View Post
            This issue can also be a control board with an intermittent problem. Was down that road on a couple of furnaces last winter.

            How can the control board have an effect upon the fan motor? 12v positive is wired to the control board, the control board is basically a bunch of on/off switches (relays) and timers. If fan motor relay is acting up there will be low or no voltage/current to the fan motor.
            Thanks Colan,

            I was thinking this as well but it seems pretty consistent in timing that the furnace needs to run longer than 45 minutes. I re-created it this morning and sure enough right around 45 minutes it started to make noise and airflow slowed down. I videoed the vent so that I could capture the noise for the dealer to hear when I tell them about it. If I knew how to post video here I would so everyone could hear it too.

            Rob
            Rob & Barb
            2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
            2022 Solitude 378MBS

            Comment


            • #7
              Calbar By the sounds of the description I would suspect either a bearing, or ice buildup on the intake fan. I lean more toward a bearing based on the noise and the slowing. As the shaft / bearing heats due to the furnace and the rotation of the shaft, both expand.

              By chance is it very Humid where you are? This could explain ice build up.
              Joseph
              Tow
              Vehicle: 2024 GMC K3500 Denali Ultimate Diesel
              Coach: 303RLS Delivered March 5, 2021
              South of Houston Texas

              Comment


              • #8
                Originally posted by Jlawles2 View Post
                Calbar By the sounds of the description I would suspect either a bearing, or ice buildup on the intake fan. I lean more toward a bearing based on the noise and the slowing. As the shaft / bearing heats due to the furnace and the rotation of the shaft, both expand.

                By chance is it very Humid where you are? This could explain ice build up.
                Thanks Joseph,

                Been a bit humid but not too bad so I don't think it is ice since the temperature has been near 32F or slightly higher. I am thinking bearings as well and have a video with sound for the dealer to listen too. Sounds like bearings and it only happens after about 45 to 50 minutes but starts slowly with little noise and then builds up to more noise and less airflow.

                Rob
                Rob & Barb
                2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
                2022 Solitude 378MBS

                Comment


                • #9
                  I would think that if it were a bearing and after this amount of time in use it would happen sooner than 45 mins. Colan has seen this issue along with plenty of others and might be on to the real issue.

                  Brian
                  Brian & Michelle
                  2018 Reflection 29RS
                  2022 Chevy 3500HD

                  Comment


                  • #10
                    Originally posted by Country Campers View Post
                    I would think that if it were a bearing and after this amount of time in use it would happen sooner than 45 mins. Colan has seen this issue along with plenty of others and might be on to the real issue.

                    Brian
                    I would tend to agree with the bearing comment as well. Paid more attention to it today since it was cold in the morning again and was the last chance to make notes for the dealer. The furnace starts making noise much earlier than the 45 mins but still blows fairly well but I can tell that the blower has slowed down from startup. You can start to hear noises very early on in the cycle if you are outside. Colan may be on to something here as well but if it was a relay and low voltage not sure why the furnace would make strange sounds. I am for sure not an expert and will be having the dealer look at it now that I know it is consistent and when it starts to act up.

                    Once I can get it into the dealer I will update this post with what they found and did to fix it.

                    Thanks,
                    Rob
                    Rob & Barb
                    2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
                    2022 Solitude 378MBS

                    Comment


                    • #11
                      Ya but, wait till you haul it down the road and it works perfectly for 2 days straight, haha. I hope you get this sorted.

                      Brian
                      Brian & Michelle
                      2018 Reflection 29RS
                      2022 Chevy 3500HD

                      Comment


                      • #12
                        Originally posted by Country Campers View Post
                        Ya but, wait till you haul it down the road and it works perfectly for 2 days straight, haha. I hope you get this sorted.

                        Brian
                        LOL!! Yes this is a concern for sure too. All that shaking could just as well make it work just fine. Wouldn't be the first time I am sure and probably be my luck.

                        Rob
                        Rob & Barb
                        2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
                        2022 Solitude 378MBS

                        Comment


                        • #13
                          I'm going to put myself out there and call it - 100% bearing issue. They will replace the whole furnace....How fast that happens? Anyones guess.
                          2018 Dodge 3500 6.7 Cummins w Aisin and 9 cup holders
                          Not to brag or anything about my finances, but my bank calls me about every day to tell me my balance is OUTSTANDING!

                          Comment


                          • #14
                            Originally posted by Scott'n'Wendy View Post
                            I'm going to put myself out there and call it - 100% bearing issue. They will replace the whole furnace....How fast that happens? Anyones guess.
                            My thoughts as well. Will confirm once I know. Just hope that Country Campers isn't right and the tow home and back to the dealer makes it go away. If it's bearings they will act up even after all the bumping around.

                            Rob
                            Rob & Barb
                            2022 RAM 3500 Big Horn, 6.7 Cummins HO/Aisin
                            2022 Solitude 378MBS

                            Comment


                            • #15
                              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.
                              Colan Arnold
                              2016 Momentum 397TH
                              Full time since 2016

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