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Old 11-21-2008, 06:20 AM   #29
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1972 31' Sovereign
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I have a question for everyone on this issue. If there is the need to open the gas line to purge the air in order to get gas to flow to the furnace, is there a reason not to just put a tee in the line above or below the furnace hand valve and then put a purge valve on that tee? It could just be another valve like the hand valve, and either run a purge line outside or just let it vent at the valve. Anyone ever try this? I figure if I have to take the furnace out to service it anyway, this would be an easy modification to make at that time.
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Old 11-21-2008, 06:34 AM   #30
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You can purge most of the air from the lines by simply lighting the stove. I would not complicate things by adding any additional valves.
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Old 11-21-2008, 07:57 AM   #31
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Just removed the old furnace from my 75 sovereign, not bad, take off the outside vent cover, you will see another plate with two wcrews into the furnace..remove them, now remove the inner front cover, the latch on mine had a screw way up top, that I got out with a stubby screw driver, take itoff. you shoudl have 4 wires hooked up to the unit, unhook them, mark what went to what.
Lower right corner on face of furnace Ihad a bolt, remove it.
On mine the gas line was on the right, had to slide it part way out of the steel case to get at it, make sure your gas is off, unhook the gas line, use a wrench not pliers. At this point it should slide out with a bit of swearing. Give it a good cleaning. once out you can hook it up to a battery and see that the electric part runs ok.
get the polarity right, tie the blue wires together and it should run. I would also pull the burner tube and clean it with a wire brush.
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Old 11-21-2008, 08:51 AM   #32
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Quote:
Originally Posted by Maxom View Post
I have a question for everyone on this issue. If there is the need to open the gas line to purge the air in order to get gas to flow to the furnace, is there a reason not to just put a tee in the line above or below the furnace hand valve and then put a purge valve on that tee? It could just be another valve like the hand valve, and either run a purge line outside or just let it vent at the valve. Anyone ever try this? I figure if I have to take the furnace out to service it anyway, this would be an easy modification to make at that time.
An interesting question and one I most admit I have thought of after have to open the gas line several times. However I think it is not worth the risk. If anything ever happened and the insurance company found that valve that would be the end.

As I mentioned above I think the air enters the lines during tank refilling when the line pressure has been reduced. I must admit I have removed both tanks more than once to have them filled. I will try not to do this again and see if the problem ever occurs again.

Historically I have had the problem first thing in the spring because I remove the tanks during the winter and both gas lines are just sealed with electrical tape to keep the bugs out. This last occurrence I had removed both tanks at a Fly J and had the problem the next time I used the heater.
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Old 11-22-2008, 07:57 AM   #33
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Something to note.
I have rehabbed about 20 campers over the years, and a point that has not been brought up. Before I fire up any of the appliances I take them out, clean them, lube them and bench test them. This saves me a bundle by not damaging units that have been off for years. Furnaces and Fridges are sure to have bees nests and spider webs and dirt. Its a pain but if you can remove the AC covers, take a hose and really washout the outside, cannot believe the dirt that comes out of the fins etc. Alittle lube on the motor, clean the fan blades, see that they are straight. Flush the holding tanks and water system, black water tanks can be really filled up, I fill it up and put a septic tank chemical in them.
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Old 12-03-2008, 06:36 PM   #34
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Well 2 full months after I started this thread I was finally able to put the time into the furnace that I needed to today. With the hours I work, kids, and trying to work on the house before the worst of winter set in I just had to put the airstream on the back burner. I started by testing the gas via igniting the chamber with a long lighter. I doubt if I would have been able to get the gas fitting off without breaking it, but testing this way worked and I was getting gas. I checked for power at the limit switch and had it so I bypassed the switch to see if the furnace would ignite. It started right up using the old starter. I put the switch back on and it started again. I put everything back together and tested it several times in which it started each time. I'm not sure if I had a bad connection at the limit switch or not before but it seems that was my problem. I'll check on the price of a new switch and if it's inexpensive I'll order one tomorrow.

Thanks to everyone for the advise.

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Old 09-11-2009, 09:21 AM   #35
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Great thread folks!

I'm also having the "pilot won't stay lit" problem, and after reading this thread and pondering the Service Manual, I'm just about ready to take mine out and have a look inside. By the way, when it runs, it runs very well; quiet and plenty of heat.

My problem appears to happen when the furnace is off, since it usually occurs after the furnace has cycled off and on several times in the night. I know when it's happened because the furnace's blower doesn't shut off.

However, I did take the exterior vent cap off to check out if something was blocking air (or exhaust) flow and found that I could not see what the "vacuum intake cup" as the manual calls it. Here's a picture of a side view from the manual:



Now, maybe my eyesight isn't perfect, but I would figure that cup should be obvious from the outside. When I looked into the opening, I thought that I could see the "squirrel cage" of the blower. I intend to check that again when I'm back next week.

ANother mystery: the manual claims that drafts shouldn't be able to blow out the pilot since the chamber's air intake and exhaust are at the same atmospheric pressure, but I DO sometimes feel a draft in the bottle-cap opening when it's windy outside. A bad gasket somewhere?

It's starting to get cold at night here, so any and all suggestions and advice would be appreciated.
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Old 09-12-2009, 09:13 AM   #36
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pilot does not stay lit

HI
done a few of these furnaces, sounds like a original Suburban. Two items to check, #1 crud on the pilot light so flame is too low. #2 Bad thermocouple, or just aloose connection. If you can reach the pilot with a "tooth brush" give it a good scrub, then blow some air at it. I ended up replacing mine as the heat exchanger rusted through..that is fatal.
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Old 09-12-2009, 11:27 AM   #37
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Thanks for the ideas, Jim.

Can you tell me where I could get a new thermocouple? Marksrv.com has some parts ofr my furnace, but I can't find anyplace wtih a thermocouple for it for sale (Suburban NT32).
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Old 09-12-2009, 01:36 PM   #38
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This is going to be my next project when i get time. I want to pull my sub and give it a good cleaning. Andy has a thread somewhere about carbon buildup inside the chamber and gently tapping it loose with a hammer.. I suspect that that is my greatest problem. The smaller volume of the chamber with all the carbon buildup.
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