Reply
 
Thread Tools Search this Thread Display Modes
 
Old 12-10-2014, 07:15 PM   #1
1 Rivet Member
 
Roaring Fork Valley , Colorado
Join Date: Nov 2014
Posts: 14
Furnace issue

Hi! I have a 1971 Overlander with what I'm assuming is the original furnace. It's a 22000 BTU Suburban, model NT22A. I've browsed some threads on here but can't seem to find my specific problem. So here goes:

The pilot lights just fine...turn the thermostat up and furnace lights just fine...however, after about 5 minutes or so, the gas supply is shutting off. The pilot goes out and everything. This happens well before the temp in the trailer reaches the thermostat set point. The fan seems to run fine...everything seems to work for a few minutes. This is a very consistent problem...as in it acts the same way every time. Kinda like when the heater itself reaches a certain temp, it shuts the gas down.

Has anyone had this particular problem and found a solution? The nearest service center is 2 hours away and I'd rather not remove the furnace and take it to them if I don't have to.

Thanks,
Gavin
__________________

__________________
gcasson is offline   Reply With Quote
Old 12-10-2014, 07:40 PM   #2
Rivet Master
 
mayco's Avatar

 
1982 31' Airstream 310
champaign , Illinois
Join Date: Jun 2013
Posts: 2,766
Limit switch
__________________

__________________
mayco is offline   Reply With Quote
Old 12-10-2014, 08:10 PM   #3
Rivet Master
 
TG Twinkie's Avatar
 
1974 Argosy 26
Morrill , Nebraska
Join Date: Nov 2009
Posts: 5,140
Images: 2
Blog Entries: 5
You may have a restriction in the duct system. Preventing air flow. Resulting in the over temp limit switch to trip.
It could be on the combustion side as well. Check for blockages in the intake and exhaust tubes.

Or it could just be a bad over temp limit switch.


Sent from my iPod touch using Airstream Forums
__________________
Knowledge: "A gift to be shared. A treasure to receive."
TG Twinkie is online now   Reply With Quote
Old 12-10-2014, 10:40 PM   #4
Rivet Master
 
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
It would not be the limit switch since the OP states that even the pilot light goes out when this happens. On those old Suburbans the pilot light is in no way connected to anything in the 12 volt electrical system.

The key here is why is the pilot light shutting down. The only thing which comes to my mind is that the thermocouple is not working right, allowing the gas to be shut down to everything, pilot and main burner.

So, the least expensive thing to try would be to replace the thermocouple. The next thing is the gas valve itself, the one the thermocouple attaches to. Unfortunately Suburban has discontinued all support for those old furnaces, parts and everything else. Thermocouples are standard items and can be found, but the old gas valve is probably much more difficult.

One other thing comes to mind. If mud daubers have gotten into the combustion system, tubes, fan, or air path, the pilot would light and burn, but once the main combustion started, without enough air through the system, the flame would go out due to oxygen starvation. That would also take the pilot light out. So, it is possible you will find a plugged combustion system somewhere. It can take a major disassembly to find that.

Lastly, the furnace is 43 years old. It is very common for those old combustion chambers to rust out and let CO into the trailer. Those furnaces were all subject to a recall due to defective crossover tubes, and the recall repair may never have been done on yours. I would also suggest you consider replacing the furnace entirely with a new one. A new one has electronic ignition, which is very nice and a new unit would be inherently safer to boot.
__________________
idroba is offline   Reply With Quote
Old 12-10-2014, 10:46 PM   #5
Rivet Master
 
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
Another thought here. What does the flame look like when it burns? You can see it through the window cap. If it is all yellow and lazy looking, you definitely have a lack of combustion air and will need to find that obstruction. If it is nice and blue and looks like a good blue gas flame, then the thermocouple or valve is suspect.
__________________
idroba is offline   Reply With Quote
Old 12-11-2014, 09:13 AM   #6
1 Rivet Member
 
Roaring Fork Valley , Colorado
Join Date: Nov 2014
Posts: 14
Thanks for the responses. So the flame burns a nice, full blue flame. I don't think anything is blocked or clogged unless it's totally internal. Seems like the thermocouple will be pretty cheap and easy to replace and the guy at the repair shop said the same. Fingers crossed it's not a gas sensor. On the bright side, it actually seems to be working better!

And I hear ya on a 43 year old furnace has probably ran it's course...but I don't really wanna drop $600 right now if I can avoid it. However, it's getting really cold in Colorado so I gotta get this thing going fast!

While we're on the subject, I was looking about taking the furnace out...and I can't even find a bolt! Where is this thing bolted down and how do I remove it? I've been in construction for 15 years so I kinda feel silly asking this question but I'm just not seeing it....


Thanks,
Gavin
__________________
gcasson is offline   Reply With Quote
Old 12-11-2014, 12:13 PM   #7
Rivet Master
 
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
I hate to be alarmist here, but $600 is cheap compared to a CO event or death. Enough said on that.

To remove: Take the outer exhaust plate off. In the center of one of the tubes you will find a long screw. Remove that and you can take the entire outer plate off, with tubes.

Inside, disconnect the gas line and the electrical lines. The furnace case has two small screws inside going into the floor, maybe an inch or so back from the face of the case. Remove those. Then, depending on how Airstream built your unit, you may be able to remove the entire furnace. If you are unlucky, there is some cabinet piece or metal right in front of the furnace so it cannot be pulled out. Those are the bitchy ones and will require figuring out how to remove the cabinets to get the furnace out! In most cases the furnace was put in, then the cabinets were built over it. Depending on the specifics, some furnaces are easy to remove, some not.

To replace the thermocouple, you will need to do a fairly major disassembly of the furnace, once you get it out. Please look at the rubber tube near the rear of the furnace which connects the combustion air route to the blower. This was the source of the major recalls on all of those furnaces. The replacement part has a red stripe on the rubber tube. That would indicate that the recall has been done. If not you have a dangerous furnace and Suburban no longer offers the recall part with the red stripe. If you find that the rubber tube is solid black, please replace the furnace.
__________________
idroba is offline   Reply With Quote
Old 12-11-2014, 03:43 PM   #8
1 Rivet Member
 
Roaring Fork Valley , Colorado
Join Date: Nov 2014
Posts: 14
Thanks so much!!

I have a sneaky feeling that this furnace did not get the recall part. I picked it up in the middle of nowhere west virginia and everything in it is still totally original. So maybe I will just drop the $600 and get a new furnace...

Thanks again for taking the time to respond. As a first time airstream owner that is living in an all original 43 year old trailer...I have alot to learn and truly appreciate the help!
__________________
gcasson is offline   Reply With Quote
Old 12-11-2014, 03:45 PM   #9
1 Rivet Member
 
Roaring Fork Valley , Colorado
Join Date: Nov 2014
Posts: 14
While we're on the subject...any recommendations for a new furnace?
__________________
gcasson is offline   Reply With Quote
Old 12-11-2014, 06:44 PM   #10
Rivet Master
 
1974 Argosy 20
2014 20' Flying Cloud
Kooskia , Idaho
Join Date: Jul 2009
Posts: 4,591
A Suburban NT 20 SQ is a 19000 btuh furnace which will probably be of a capacity large enough for your use, if you had an NT 22. They no longer make a 22,000 btuh furnace in the NT series and a 30,000 would be overkill.

You may have to mount the new furnace on a platform to have it fit the original holes in the side of your trailer but I believe it will fit just fine otherwise.

The amp draw of the new unit will be lower than the original by about 1/3 and it has electronic ignition, so no lighting of the pilot light.
__________________

__________________
idroba 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 issue turns out to be AS issue 92landyacht Land Yacht/Legacy Motorhomes 16 01-20-2016 11:19 PM
Another Furnace Issue PharmGeek General Repair Forum 13 04-19-2014 05:22 PM
Argosy Furnace issue mprokop87 Argosy Motorhomes 0 03-11-2014 07:25 AM
Atwood furnace issue--Help?! Silvertwinkie Furnaces, Heaters, Fireplaces & Air Conditioning 9 03-01-2005 09:31 AM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 08:52 PM.


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.