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Old 04-20-2021, 07:28 PM   #1
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Furnace repair

Last summer was our first having adventures in our new camper and we were so happy to just be able to get our and about safely despite COVID. I was able to get the stove top working, but that is the only propane appliance that we've been able to use. The refrigerator works on electric, but I can't get the propane to light, the stove top works and the pilot in the oven, but not the oven, and while the blower works just fine, the furnace will not light. Right now, I'm working on the furnace because it would be nice to be warm on the cool spring nights.

- The blower works fine. I can't get it to light and I can't smell any propane smell so I think none is getting released, but I know that the line is at least partially clear because the stove top lights just fine.

- I have use a vacuum cleaner and an air compressor to attempt to clean out everything I can see without yet taking anything seriously apart.

- From what I have read there could be several things causing this problem. It could be the sail switch, it could be a clog somewhere in the propane line that doesn't impact the stove, it could be a clog in the combustion air intake.

? Does anyone have a suggestion what to try next?

?I'm not actually sure what the sail switch looks like on a 1983 hydroflame furnace, is it what is labeled a 'limit switch' in the diagrams?

? how difficult is it to simply take the whole unit out, take it apart, clean it, put it back together, and reinstall it?

I'm including a bunch of pictures of our setup for context, any thoughts or insight will be greatly appreciated!

Miles







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Old 04-21-2021, 08:37 AM   #2
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If you can't even get the pilot to light, I'd start with turning the gas off, disconnecting the gas line at the furnace, and then have someone turn the gas on while you monitor that line to see if you get any flow. If you do, of course the first thing you want to do is turn the gas back off and allow what's hanging in the air to dissipate before doing anything else. Then reconnect the line.

If you don't, You're going to have to track the line back to where it splits off from the feed to the stove, looking for any kinks or maybe even a valve that's turned off.

Does the manual ignitor spark as it should?

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?I'm not actually sure what the sail switch looks like on a 1983 hydroflame furnace, is it what is labeled a 'limit switch' in the diagrams?
The limit switch, shown in the parts breakdown, is heat-sensitive. If it sees the burn chamber overheating, it opens to shut down gas flow. The sail switch is inside the blower. It has a paddle that senses whether the blower is moving air. If not, it opens to shut down gas flow. The two switches are in series with each other. Neither one will prevent the pilot from lighting.

If/when you can get the pilot to light, if the main burner still won't start, we need to get into some electrical troubleshooting. Let us know...
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Old 04-24-2021, 08:23 AM   #3
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This may help, a few docs for you. You might have one of them already, but the service manual maybe not.

This is an installation manual for the FA-7920 here in the forum files section. It may be what you have. You need to be logged in to download a copy. https://www.sunlineclub.com/forums/d...o=file&id=5639

Here is a service manual on the FA-79 series furnaces. Your FA-7920 is a FA-79 series furnace with the 20,000 btu rating. The last 2 numbers change for the btu rating.

Page 28 starts with the FA-79 series. You need to look for the "pilot" version and not the DSI (direct spark ignition). This is from Bryant RV, they are a good help on these system. Scroll down the the 1980's Hydroflame area where it includes the FA-79 furnace.
Service Documents and Manuals

When you mentioned
Quote:
? how difficult is it to simply take the whole unit out, take it apart, clean it, put it back together, and reinstall it?
I myself would do just that. You have no idea what shape the combustion chamber is in on a system this old. Or if the safeties work. You can trouble shoot the whole system on the bench, you just needs a regulated down gas supply, (11" WC) and a 12 volt DC battery. Do not hook this up to a standard BBQ grill gas regulator, they are on high pressure, you need to step it down to 11" WC pressure. The good news, your blower is running. That is a good first step.

If that is too much for you, then find someone who has worked on LP gas systems to help. There is risk involved. Odds are, this is in your gas valve, or the supply to the gas valve. If the pilot will not light, you will not get to the main burner lighting.

Finding parts is going to be complex if the gas valve is bad or cannot be cleaned up. The part numbers in the service manual may be superseded or discontinued. Atwood sold out to Dometic and something this old, Dometic does not seem to be supporting a lot of the old low volume parts any more.

This link shows the bench test on a much newer furnace I was doing, but shows what it involves on the bench test. Scroll down a little to the furnace tests.
https://www.sunlineclub.com/forums/f...tml#post154909

On your fridge that will not work on gas, the good news, it works on electric and that is a major step. Create a post on it with pics and the model of the fridge. The older fridges are fairly simple. It too may have a gas blockage which may be part of the furnace issue.

Hope this helps and let us know how it goes.

John
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Old 04-29-2021, 10:28 AM   #4
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Here's a simple trick that I was lucky to have an "old timer" teach me on my first camping trip. When starting up the Water Heater, have your stove burners running. I have done this every time for 20 years. My furnace (Atwood) started not igniting a couple of years back and I found that the stove burners trick worked for it too. I had to do this last weekend on "opening day".
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