Furnace fan does not move air through ducts/vents

[taylor.coyote 4]

camping off the grid in the cold (17-20 degrees in mornings). furnace lites and generates a great deal of heat in the hull cabinet but does not blow air through the ducts/vents. we can get more heat into the trailer by taking off the mattress and taking off the fiberglass hull lids under the bed. this brings more heat into the trailer than is coming from the vents.. i'm assuming the furnace has a fan that is not running.. adjusting the fan speed at the thermostat does nothing. any suggestions on how to get our furnace fan to run?

[John E Davies 333]

The furnace fan is REALLY loud, you know when it is running. I am not sure if it has a separate fuse than the rest of the unit, but I doubt it. So when the unit lights and heats up, the fan should also be powered on. Are you positive that you don't simply have all the air control vanes closed completely? That would restrict airflow significantly. Also the return air register should be open.

 

You can remove the movable vane in the bathroom heated duct so that it is unrestricted, to heat that room a little better, but you should keep the other two in place for temperature control (distribution). To get the vane out, pry off the round cover carefully.

 

Good luck. I hope you have an aux source for heat....

 

John Davies

 

Spokane WA

 

 

[mountainoliver 17]

Typically the furnace will not ignite until a proof of fan switch is made. In other words, the fan must be running first then the burner will ignite. Either all of the register dampers are closed or the ducts are not attached to the furnace. Check both of these things.

[SeaDawg 292]

What is your battery voltage reading? I think there is a safety cutoff on our furnace fan at low voltage. Ours is 12 years old, though. Not the same model.

[taylor.coyote 4]

all the vents are open and i have checked to see they are hooked up to the furnace. we do get the sound of a fan but nothing blowing through the vents. have checked for separate fuse but seems the furnace is all on one 7.5 amp fuse. the various times i have tried to get heat/air flowing through the vents, my batteries have been between 12.4-12.7

 

the furnace is clearly working because its very, very warm in the hull under the bed. it becomes so warm in the hull under the bed that Im concerned it's a safety issue and have stop running the furnace. seems that either the fan is not working (but it makes a significant sound like a fan) or something is plugged in the ducting... maybe we have a critter nesting in the ducts..

 

thanks for the tips but none have solved the issue.. please let me know if you have any other ideas

[ScubaRx 105]

As Ken pointed out, if the furnace is producing heat, the fan has to be running. By your description of what’s happening, I suspect the main duct hose has come loose from the furnace and all the heat is spilling into the basement (tween decks) area. To check, remove the access cover at the curb side rear under the mattress. You should be able to immediately see if that is the issue.

[Overland 499]

Our furnace has ducts coming off two sides, so be sure to check them both. Having one off would probably reduce the pressure to the other to zero.

[taylor.coyote 4]

pulled both duct hoses (both sides) and ran the furnace.. plenty of heat but no air blowing.. we will be home in two days and getting to warmer weather. talked with my rv repair guys and have the trailer set for them to help me with the heat issue.

 

thanks to all

 

 

[John E Davies 333]

NT entered in error.

[mountainoliver 17]

Wow! That’s a little unsettling, that means the sail switch that detects air flow/fan turning is maybe stuck in the “made” or air is flowing position. That one little switch is supposed to prevent the burner from igniting if there is no fan to cool the fire box or to provide combustion air flow. (two different fans/one motor on the Suburban furnace) The burner will ignite if there is no combustion air flow but will not ignite if there is no air circulation flow to cool the fire box as the switch only detects the latter. I wouldn’t use the furnace until you can figure it all out. No air flow is a dangerous situation.

[mountainoliver 17]

Also, I forgot to mention that there should be an over temperature switch to shut everything down if all else fails. At least I would think that there should be?