Coleman Furnace has high pitched hum

LJ-TJ · October 16, 2017, 03:00 PM

So interesting had trouble keeping the furnace lit. Found out there's a fail-safe scenario in that if the house battery isn't fully charger or has a certain amount of charge in it the furnace won't light. Seems right because once I plugged into shore power she fired right up.HOWEVER no she as a high pitch mum in it. It quits down for a short period but then fires right up in a hum again. If I go out side and put my hand near/over the exhaust for a sec. the hum disappears, as soon as it starts up again the second I put my hand over the exhaust it disappears. Anybody got any thoughts.

Rickf1985 · October 16, 2017, 05:36 PM

You are restricting the air flow and the blower is stopping probably. The heater should shut off at that point. The reason it doesn't run on a low battery is probably weak spark or not enough voltage to the blower to keep the sail switch open.

LJ-TJ · October 16, 2017, 05:47 PM

Thanks Rick but how do I fix it. Or do I have to buy and new furnace. I've been looking for on for part to no avail. Hm?

DaveVA78Chieftain · October 16, 2017, 08:44 PM

Low voltage results in low blower speed that does not allow the sail switch to engage.

High Pitch hum could be:
1) Dirt, leaves, or insect nest build up on blower fan creating an out of balance situation
2) Brass blower motor bearing (1 on each end of motor) needs oiling. Bearing may have a felt oil wick.

Rickf1985 · October 16, 2017, 09:12 PM

Or a bees nest in that exhaust tube blocking some of the exhaust flow. Get a good look see in there if you can. Also check your electrical grounds on the heater.

LJ-TJ · October 16, 2017, 10:03 PM

Thanks Guys, I'll get on it tomorrow.

RANGERRICK · October 18, 2017, 06:17 PM

You may need a new burner.What happens over the years is that the slots in the burner get larger because of rust and wear causing your air fuel mixture to change.That is why the humming noise went away when you changed the air flow.I know this sounds off the wall.
That's assuming that the bushings in the motor are good.
Back in the 70's i spent hours trying to figure out where that sound was coming from.
I don,t want to make it sound like a sales pitch,but i may have a burner and or a blower motor for that heater.I would just need the model#.

DaveVA78Chieftain · October 18, 2017, 07:18 PM

QuoteYou may need a new burner.What happens over the years is that the slots in the burner get larger because of rust and wear causing your air fuel mixture to change. That is why the humming noise went away when you changed the air flow. I know this sounds off the wall.

That is not off the wall but a very real possibility.

Sasquatch · November 20, 2017, 07:42 AM

My Coleman has been doing that for as long as I can remember, 20+ years. First start up cold has a humm. It's not a bearing noise, more like a resonance caused by air flow. Only lasts for 15-30 seconds, just long enough for the burner to warm a bit then goes away. I pulled it out of the coach a couple years ago during my remodel. Tore it down and checked everything out inside. All was good. Furnace always works, and the noise has not changed one bit in the 20+ years I have used it, so I just mark this as the "character" of my old coach.