Noise when Furnace fan starts

[colemole]

I am the proud new owner of a 2003 Adventurer 35U. I find when the furnace starts to blow there is a fairly loud clang as though there is a loose piece of tin in the plenum and a lesser clang when the blower stops. The dealer told me its the expansion /contraction of the plenum which is under the bed and there is nothing can be done. True? Common issue?
Thanks

[InPursuit]

Quote:

Originally Posted by colemole The dealer told me its the expansion /contraction of the plenum which is under the bed and there is nothing can be done. True? Common issue?

The SALESMAN told you.
Dealers LOSE money doing repairs.

The squirrel cage fan is mounted in a rather tight fit housing but it is on bearings and should NOT be making sheet metal banging and clicking noises.

It's probably a very minor thing to remedy.. like something is loose or something has found it's way into one of the openings. Someone will need to open up the cover (6-8 screws on the side wall) and look into it.

If it (the source of the noise) is deeper into the unit... then the duct hoses and the LP pipe will need to be disconnected so the housing can slide out through that side wall opening.

[GENECOP]

[QUOTE=colemole;667832 The dealer told me its the expansion /contraction of the plenum which is under the bed and there is nothing can be done. True? Common issue?
Thanks[/QUOTE]

[colemole]

Furnace exhaust comes out through the rear end of the RV unit as well as the larger opening which has 4 screws and 6 in the exhaust ports. Is this what we are talking about opening up?

[InPursuit]

Quote:

Originally Posted by colemole Is this what we are talking about opening up?

Are you asking me?
I was referring to plain vanilla ATWOOD RV furnaces that are in (a guess) 80% of RV's on the road today. And yeah, the flue vent ports through that shroud opening too.

If I'd ever gotten around to shrinking my digital pics I'd post one.
Inside (under the sink) you'll see the square sheetmetal housing that has the flex duct attached to it.

[Old Snipe]

I had the exact same MH and my furnace did the same thing. There is a metal door in the ducting off the furnace that is spring loaded and would make a minor metallic sound when it closed after the furnace blower shut off.

Normal, nothing to worry about.

Best Regards!

[DancinCampers]

There is a hinged door at each end of the ductwork that runs under the floor. The rear one opens when the LP furnace is running, and the front one opens when the Aux Coach Heater is running.

The doors are hinged at the top, and they keep the air in the ductwork from escaping anywhere except the floor registers.

Sounds like it is working ok, I'm not sure if they put bumpers in there or not.

[colemole]

That's what it sounds llike, a tin door opening and closing. Guess we are okay. Thanks all

[Clay L]

For what it's worth, Winnebago uses Suburban furnaces.
All of the ones I have seen can be removed without messing with the duct work or hoses by removing one screw in the bottom front center. It has a sticker next to it that says "Remove for service". With it out and the propane line disconnected the furnace can be pulled out leaving the plenum behind.

[Hikerdogs]

I believe what you're hearing is what's called the "sail Switch" It's a sheet metal door in the heat exchanger plenum. It makes a clanging sound when it opens and closes. If you follow the start sequence carefully you'll notice the blower starts a few seconds before the furnace actually fires up. When the blower starts the air flow opens the sail switch. The sail switch makes a contact verifying the heat exchanger blower is actually working, It's a safety device insuring there is air flow before allowing gas to flow into the combustion chamber and ignite.

If for some reason the blower doesn't produce enough air flow to open the sail switch the furnace will not start. If the furnace did start without sufficient air flow the plenum could get hot enough to start a fire.

[FDchief]

Mine makes noise when it shuts down.