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?
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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 The part numbers in the service manual may be superseded or discontinued.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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