Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-01-2016, 07:56 PM   #1
3 Rivet Member
 
GreggH's Avatar
 
2005 31' Classic
Castalain Springs , Tennessee
Join Date: Jan 2006
Posts: 205
Furnace blower spontaneously came on

Problem: Furnace blower came on w/o turning it on.

Last night camping on SC beach, temp around 70, windows open, a little humid, thermostat control was in the off position, the furnace blower started spontaneously. I went over to the thermostat control, turned it to the on position and nothing happened, including not lighting up as normally turning it on. Did this a couple of times w/o any results. Went under couch and turned 12v disconnect off and blower, along with every other 12v, went off as it should have. I then turned 12v back on. The blower started on again, went over to T/control, turned on and this time the control lit up. Turned it to fan only which did start the a/c fan and the blower went off a couple of seconds after.

Now the furnace never kicked on but I don't know it ran long enough for the normal delayed firing to occur. Same with turning off, there is always a delay from when the blower receives a signal to shut off to when it actually goes off so I'm not sure if it was the turning off the 12v system or turning the thermostat to fan that turned off the blower. I tend to feel it was turning the 12v system off then on that did it.

Wasn't able to do any work on it today. I have the thermostat control unplugged right now but everything else is normal.

Any comments. Are you out there Howie?
__________________

__________________
GreggH is offline   Reply With Quote
Old 05-01-2016, 08:29 PM   #2
4 Rivet Member
 
trekerboy's Avatar
 
1979 31' Excella 500
Charlevoix , Michigan
Join Date: Aug 2014
Posts: 318
What make and model furnace do you have?
__________________

__________________
trekerboy is offline   Reply With Quote
Old 05-02-2016, 03:22 PM   #3
3 Rivet Member
 
GreggH's Avatar
 
2005 31' Classic
Castalain Springs , Tennessee
Join Date: Jan 2006
Posts: 205
Sorry for the delay, we moved today.

The furnace is Atwood, 34,000 btu which is 8535-IV model.
Thermostat is Duo-Therm "Comfort Control Center"
__________________
GreggH is offline   Reply With Quote
Old 05-02-2016, 04:15 PM   #4
Rivet Master
 
Foiled Again's Avatar
 
2012 25' FB Eddie Bauer
Vintage Kin Owner
Virginia Beach , Virginia
Join Date: Sep 2004
Posts: 5,883
I hate electrical problems - but this sounds like a short somewhere. If your furnace is on a separate fuse/breaker, pull it until you get to a destination that allows you to have time to really trouble shoot it. literally sounds like a floating short somewhere.
__________________
Today is a gift, that's why they call it the present.
Foiled Again is offline   Reply With Quote
Old 05-02-2016, 04:28 PM   #5
Rivet Master
 
2014 20' Flying Cloud
Long Island , New York
Join Date: Jun 2015
Posts: 6,351
I'll go with the short-circuit suggestion also. FYI here is another thread in which a crazy short (furnace blower and radio -- go figure!) was the problem:

http://www.airforums.com/forums/f44/...ue-148768.html

Sorry I don't have the expertise to help with the specifics of your problem.

Good luck!

Peter
__________________
OTRA15 is offline   Reply With Quote
Old 05-02-2016, 05:32 PM   #6
Rivet Master
 
Gene's Avatar
 
2008 25' Safari FB SE
Grand Junction , Colorado
Join Date: Sep 2007
Posts: 10,840
Or change the thermostat, the easiest thing to do. You can test the circuits on it with a multi tester if you have wiring diagram for it. It may be online.

Gene
__________________
Gene is offline   Reply With Quote
Old 05-02-2016, 07:19 PM   #7
2 Rivet Member
 
6PackCharlie's Avatar
 
1995 30' Excella
Logan , New Mexico
Join Date: Feb 2005
Posts: 90
If I am reading your post right, you were not connected to shore power? If you were using batteries, you may not have had enough juice to spin the blower fast enough to make the "sail switch" activate.
I have a problem when I boondock. The first couple of times the heater comes on it works fine. But then the batteries get a little weak and the blower (probably need to get a new blower motor) does not spin fast enough to get the sail switch to connect. The blower will run non stop because the gas does not come on. When I am connected to shore power, the heater work fine.
I sometimes carry a third battery and connect it to the other two or more conveniently I leave my tow vehicle plugged in and that keeps the heater going all night.
__________________
Charles & Annette
WBCCI # 1407 -- Member 4CU
1995 31' Excella
Dodge 2500 Diesel-Tow Vehicle
___________________________________________
6PackCharlie is offline   Reply With Quote
Old 05-03-2016, 02:11 PM   #8
Rivet Master
 
1996 25' Excella
Tillsonburg , Ontario
Join Date: Aug 2014
Posts: 787
A spontaneous start sounds like a set of contacts that shorted or maybe did not open fully on last shutdown. The outside temp might have warmed things up enough to allow the contacts to touch and power the fan. If it cleared itself it may never happen again or it may become intermittent and the only way you might find it is to disconnect power and then go looking at contacts with a continuity meter....or obviously send it for service. A good look at the circuit diagram might give a lead as to where to start trouble shooting.
JCW
__________________
JCWDCW is offline   Reply With Quote
Old 05-03-2016, 06:51 PM   #9
"Space A" S/O Registry 11
 
2006 34' Classic S/O
Fort Worth , Texas
Join Date: Feb 2007
Posts: 550
Try rebooting the T-stat. Look it up under Dometic. However, I am inclined to think a relay is sticking too. Ask lewster, he knows Dometic in side and out.
guskmg
__________________
guskmg is offline   Reply With Quote
Old 05-03-2016, 07:55 PM   #10
Rivet Master
 
A W Warn's Avatar
 
2000 25' Safari
1999 34' Excella
Davidson County, NC , Highlands County, FL
Join Date: Aug 2006
Posts: 2,568
If the thermostat was calling for the furnace to come on, there would have been ignition. This rules out the thermostat. (unless there is a "fan on" function for your furnace. My CCC fan function only turns on the rooftop fan, not the furnace fan)

If the thermostat wiring short circuited so that the furnace fan came on, there would have been ignition. This rules out a short circuit in the thermostat wiring. (the furnace control wiring is two blue wires, so it is either on or off. There is no furnace fan only option on any I've seen)

I think the problem is internal to the furnace. I would suspect moisture on a circuit board, an insect on a circuit board, or a bad circuit board. If you continue to have this problem, get someone who is knowledgeable to diagnose it.
__________________
A W Warn is offline   Reply With Quote
Old 05-03-2016, 07:56 PM   #11
Rivet Master
 
Boxite's Avatar

 
2008 22' Sport
Spicewood (W of Austin) , Texas
Join Date: Mar 2015
Posts: 1,230
Some furnaces have a thermistor which powers the fan until the plenum cools down after the thermostat shuts off the propane. I.E., if the thermistor fails it may think the furnace had been running previously (whether it had been or not) and the plenum had not yet become sufficiently cool to shut off the fan.
Just thinkin'....
__________________
2012 Ram 1500 Crew Cab 4.7L 4X4
Rambox
WBCCI 14676 TX ALAMO UNIT
Boxite is offline   Reply With Quote
Old 05-03-2016, 08:04 PM   #12
3 Rivet Member
 
GreggH's Avatar
 
2005 31' Classic
Castalain Springs , Tennessee
Join Date: Jan 2006
Posts: 205
Thanks for the replies.
I've had the t/control unplugged until today. It got too hot so needed the a/c on and plugged the t/control back in and all has run as normal. We've been on the road for 3 weeks and haven't needed the furnace heat or ac until today. Earlier we did have the heat pump on at night and it ran normally. As a matter of fact, I can't remember the last time we've had the furnace on, honestly it might be 2 years or better. Short or relay sounds right. I had to replace the t/control 2 summers ago so that's fairly new, but not impossible. If there is a next time won't be so quick to shut it off to see if the furnace would have fired up and after shutting off the 12v, give the blower a chance to shut off as I turn things back on to see if involves the t/control. I checked what I could w/o major disassembly and nothing obvious. Will investigate better when home. The pain about phantom elect problems is you never know when they pop up again or if they will.
Thanks again.
__________________
GreggH is offline   Reply With Quote
Old 05-03-2016, 09:00 PM   #13
Rivet Master
 
A W Warn's Avatar
 
2000 25' Safari
1999 34' Excella
Davidson County, NC , Highlands County, FL
Join Date: Aug 2006
Posts: 2,568
I doubt you could have reacted fast enough to stop the furnace from igniting if the thermostat called for the furnace to come on. It takes only ~15 seconds for the fan to run enough to move sail switch to allow the furnace to ignite.
__________________

__________________
A W Warn is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Furnace thermostat connection came loose... CraigCA 1970 - 1973 Sovereign 0 10-22-2015 09:33 PM
Furnace Blower Noise Lumatic Furnaces, Heaters, Fireplaces & Air Conditioning 22 03-01-2013 12:00 PM
Centramatics for the furnace blower Jammer Furnaces, Heaters, Fireplaces & Air Conditioning 6 12-08-2010 12:03 AM
'71 overlander furnace igniter came loose zigzag Furnaces, Heaters, Fireplaces & Air Conditioning 0 11-24-2010 10:05 PM
Hydro Flame furnace blower quit working won't start nsteel Furnaces, Heaters, Fireplaces & Air Conditioning 3 01-04-2010 04:27 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 04:35 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.