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Old 09-23-2012, 03:40 PM   #1
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Furnace lit, but no heat

1973 Ambassador with original Suburban furnace as far as i can tell.

This is my first attempt to get it working before we go camping next month. I can get the pilot light lit with a camp lighter, bu thats all i can figure out.

I followed the instructions on the furnace. i turned the thermostat up, turned on the tanks & opened the valve.

1) There is a metal rod by the pilot view hole, im not sure what this does, but it didnt seem to make any difference, by moving it in any direction.

2) I removed the cover, Im assuming that the push button at the bottom left is some kind of electric ignitor.

3) Since i have duct work, im assuming there should be a fan somewhere? Theres no fan under the heater, just open ductwork. a bundle of wires run to the furnace and a couple go to what i call the ignitor and the rest disappear in the back.

4) Ive checked the fuses and breaker, im assuming i have no fan or its mounted in the very back somewhere?

5) Ok, the pilot is lit...now what? How do you turn up the gas? All i have so far is a lit pilot light.
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Old 09-23-2012, 04:19 PM   #2
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The furnace will not run without 12 volts DC. If you have glass fuses, make sure they are tight in the holders. If you have new spare fuses, start swapping them out. Size for size. You could try removing the thermostat from the wall and jumper the two wires together.
You should hear a click when it starts as the fan relay clicks in. If I remember correctly the burner will not light unless the fan is running.
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Old 09-23-2012, 04:37 PM   #3
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If the fan is not running the gas valve will not open.

When the unit call for heat the fan will come on for about 20 seconds to purge the combustion chamber. At that point you should hear the gas valve click open and the burner should fire.

If you do not have the fan running that is the point to start checking. Check for 12 volts at the furnace. If you have power at the furnace you may gave to remove the unit and get to the fan to test for voltage at the fan and then test the motor itself.
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Old 09-23-2012, 05:28 PM   #4
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If you remove the furnace check for rust many have had furnaces rusted through, check it in place as much as possible.
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Old 09-23-2012, 05:29 PM   #5
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I checked & I have 12 volt at the red & yellow wires at the furnace. I also jumped the thermostat & checked the fuses. Relit the furnace, nothing.

How do i get to the fan? How do i get the furnace out, without tearing the cabinet out?
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Old 09-23-2012, 06:54 PM   #6
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I checked & I have 12 volt at the red & yellow wires at the furnace. I also jumped the thermostat & checked the fuses. Relit the furnace, nothing.

How do i get to the fan? How do i get the furnace out, without tearing the cabinet out?
Remove the bottom rail of the galley cabinet.

An almost 40 year old furnace should "NEVER" be ateempted to be used, until it is taken out, placed on a bench, and then taken apart.

You will be amazed as to what is typically found inside the heat chamber.

Replace all the gaskets when you reassemble the furnace.

Anything gas or LPG fueled appliance, can be a super safety hazard.

Don't assume, but dig into the issue from A to Z, so that you are absolutely assured of properoperation AND safety.

LPG furnaces do indeed have the ability to explode,as many of them in the 64 models have done, etc.

Andy
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Old 09-23-2012, 09:40 PM   #7
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Well should I just replace it? I don't want to blow up. How much does it cost to rebuild it?
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Old 09-23-2012, 09:49 PM   #8
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If it is original, and a 73, my recommendation is to replace it. You can repair or rebuild things for sure, but the newer ones have electronic ignition, and will take a little less 12 volt power to run.

40 year old furnaces have so many possible problems it is just not worth the fight. Fix one, another pops up, like whack-a-mole.
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Old 09-23-2012, 10:09 PM   #9
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Well should I just replace it? I don't want to blow up. How much does it cost to rebuild it?
Basically, a 40 year old furnace, has served it's purpose.

It's life probaly could be extended, at some expense.

How much expense, depends on what you would find when you dissasembled it.

Depending on how many hours it's been used, the motor might need to be replaced. A 40 year old motor will be very expensive and hard to find.

At least if you replace the furnace, you will have peace of mind for many years to come.

Andy
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Old 09-24-2012, 12:30 AM   #10
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These threads helped me understand a lot. Maybe there are other helpful posts on Airforums.com. My furnace is original to my 1968 Trade Wind. I have not been camping or traveling in winter, so I can't say much, just that I know it works well.

I had mine bench tested at a shop that repairs RVs, repairing and replacing the cores of ammonia evaporation refrigerators/freezers. If you are close to Indianapolis, I can forward his info to you. If so send me a PM.

Hint on searching:
In a browser search field type

Site:airforums.com Suburban furnace
Or
Site:tompatterson.com Suburban furnace

Searching this way will return a lot of matches.

Searching within the forum drives me crazy, unless I am looking for a specific person or topic. To me, it sounds like you want to find out how to maintain your furnace so it will operate safely for your camping. The second post goes into great detail about what and what not to do to test, clean, and maintain. Consensus is to seek out a professional to look the furnace over thoroughly.

Tom's posts are archived, some 12 years and older, quite vintage-relevant.

http://www.tompatterson.com/Airstrea....php?947892878

http://www.tompatterson.com/Airstrea....php?948279679
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Old 09-26-2012, 12:21 PM   #11
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Furnace

Ok, i managed to wiggle a broom stick back to the fan motor & the squirell cage spun freely.

1) I found the red & white wire from the fan running to a relay on the side of the furnace, i disconnected the connector and stuck the hot wire from my 12 volt to it, the fan roared to life.

2) I then switched on the thermostat & lit the furnace, it came on heated the trailer in minute.

3) Now...I disconnected the red hot wire from the fan wire (expecting the fan to go off) the fan kept running, even with the relay not connected to the fan (seems odd).

4) I turned the wall thermostat off & the main heat went off, back to the pilot light.

5) I turned the gas off, im letting the furnace cool off so i can reach back there & hook the fan motor back up to the relay....

6) Whats up? (seems odd to me the fan kept running when not connected to the main wiring).....

7)
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Old 09-26-2012, 12:38 PM   #12
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Sounds like the original problem was a stuck fan shaft. Once you freed it the fan ran.

Now for why the fan ran when you thought you had removed a source off power can only mean you had not disconnected the power. There may be 2 sources of power to the fan motor. A start mode for the purge cycle and a run mode, feed by the relay once the purge cycle is over.

In any case once it cools down it should start and run.
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Old 09-26-2012, 12:45 PM   #13
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I reconnected the red/white fan wire back to the relay, im back to the original problem the fan want kick on with the furnace.

I assume the silver relay on the furnace is bad???? Or am i missing a step?
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Old 09-26-2012, 12:45 PM   #14
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Don't do like I did. Replace the sucker. Even if you get it running you will continue to have problems. You can get a brand new, and better, Suburban for $400- $600 and peace of mind. Or you can check into replacing with an Atwwod which is more efficient according to posts in the forums. Another option is a catalytic heater, which has pros and cons. Pro-no moving parts. Con- heats objects not spaces, needs a window open for safe use.
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