Furnace troubleshooting, anyone?

[Bill Ruh]

Hi Sam,

Our 14-year-old suburban furnace has been pretty bulletproof, so my first guess is an immobile fan and second guess is a wiring short.

If the fan can't turn (frozen or blocked, say by an insect nest) that could cause a big current draw on the motor. You can look at the inlet and exhaust ports (our suburban has a vertically stacked double port and nearby single port); if that's blocked, then that is certainly a problem.

You may be able to get to the electronics without removing the unit, so that would allow measuring voltages to see if the problem is the wiring to the unit.

But to really see what's going on, you may have to remove the furnace, which isn't too hard. After disconnecting the gas and a few screws, ours slides toward the inside (the outside vents needn't be removed). That exposes one of the fans, so you can see if it turns freely. Our electrical harness was long enough to run it in the aisle without gas.

FWIW, our suburban has a single motor that drives 2 fans, one for outside air and one for inside. Once that starts, the fans blows a "sail" switch into the "on" position, which starts the furnace after a delay. If the fans don't work, the sail switch stays off, preventing gas and ignition without proper ventilation.

[Mike Jean Bandfield]

Mud wasps are a common problem. They get in through the exhaust port and build their nests around the fan blades blocking them from moving. The RV stores carry a stainless steel screen formed like a rectangular bowl that fits over the furnace vent and attaches with springs that hold it in place. They sell for about $30.

I found a stainless steel soap dish at Walmart that works in much the same way for $5.

Sam, I hope the fuses protected you from serious damage to the furnace components. The really good news is the fuses were there and worked to prevent a fire while you were sleeping.

Mike

[w5vthdonb]

I talked to Suberban years ago about putting a screen over the vents on the outside and they replied if you do, don't use the furnace till you removed them as the screens restrict the air flow and could over heat the heating chamber, and you could have a fire. I saw the results of this one day at a ralley of what they were talking about. If you ever sat in a screen tent in the summer and went outside and the wind was blowing just a little you can feel the diffrence. I use to install the screens for the summer as we lived on a lake and you sure did get the dirt dobbers and removed them in the winter. Now I just install a brass scrubber which you can find in any grocery store in the summer and remove them in the winter or when I want to use the furnace. This is easier than removing the unit to get rid of dirt dobbers and it only takes a couple of seconds with nose pullers.
I think if you look at Camping World catalog they may or may not sell the screens any more. At one time they removed them from their catalog.
Don USN ret
2002 26' RSB
1987 VW Cabriolet toad

[Bob & Barb Garner]

We had the same problem. We were on our way to the factory at the time. Replaced the fuse twice. When we got to the factory the techs tried it with a new fuse once again. It worked!! They couldn't find any problem. We have not had a problem since then, and that was 3 years ago. Must have been grimlins!!

Good luck!

[Mike Jean Bandfield]

the screens restrict the air flow and could over heat the heating chamber

That would certainly be a problem with a screen placed tight over the ports reducing the ports' area. An extended box shape results in ~50 square inches of screen surface. There's no restriction of any consequence if done properly.

Mike

[Bill Ruh]

Nice work, Sam!