Furnace operation

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seabreeze331

seabreeze331

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Joined
Feb 17, 2010
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345
Location
Fl panhandle
The Atwood 8940-III- DCLP in my adopted 5r was working good until the owner had a professional RV inspection on it. Now it fires but want burn.
The blower comes on, ignitor fires and I hear a burst of flame but no sustained heat.
I'm thinking blocked intake or exhaust but can't find anything on how to clean them. Unless I missed it, Gary left that part out of the guide  :D.
So, where do I start?
 
Do you feel a good strong flow of hot air from the exhaust? (Start with hand at least 1 foot away). if so there may be a blockage. Can not help you with that.

In my case the "Blows, ignights, then goes out and does it two more times and locks out) was a bad control board. I went with a Dinosaur replacement, Very happy.
 
There seems to be good air output but it's not hot.
Haven't done any testing yet. They just got back from a long weekend with it and I was going to use it.
Wanted to start with the simplest fix and work into it.
 
That's the guide I referenced that didn't address cleaning intake / exhaust.
But you're right about Gary's presentation. If I had his brain I wouldn't need my money, oh wait  :p I don't have money.
 
[quote author=seabreeze331]That's the guide I referenced that didn't address cleaning intake / exhaust.[/quote]

Oops, apologies, I missed that in your original message.
 
If the burner lights and then goes out about 10-15 seconds later, the problem is the flame sensor. If the controller does not get positive feedback from the igniter/sensor within a short time, it shuts the gas valve off and lets the fan continue to run to clear any gas fumes.

If you had an intake or exhaust blockage, 99% of the time it would not light in the first place.
 
Thanks Gary.
More troubleshooting: Remove and cleaned draft cap assembly, cleaned blower blades, got 13.45VDC, sail switch works, cleaned board connections, plenty of gas. 12VDC at gas valve until flame stops (just like you said).
Will take control board to have it checked at local RV repair shop.

The burner fires but goes out within 2-3 seconds.
I don't see a flame sensor on the hydro flame 8900-III series parts breakdown. There's a burner assembly and electrode.
 
There's a burner assembly and electrode
Click to expand...

If that  electrode mentioned sits in the flame, it is also the flame sensor (it has a dual function).
 
Got ya. Yes the electrode goes into the flame. This is a real learning experience.
Thanks to all for the help. I know it's not cold now, but if it's there it should work, right :mad:
 
I seriously doubt of the control board is the problem, but it never hurts to check.  If the igniter/sensor electrode does not return a "flame present" signal to the controller within 6 seconds, the controller shuts the gas valve off.  The signal is a very small voltage generated by the sensor tip, so  a poor connection at the controller board is a common cause of signal loss. You cleaned it, but that's still a prime suspect. The igniter/sensor itself is the other likely cause, and they aren't expensive to replace so maybe worthwhile just to eliminate the possibility.

If you have a second furnace, you can swap parts to find the failure point.
 
Didn't get a chance to have control board tested.
The spade clip for the electrode lead on the control board was loose so I replaced it and brushed the ignitor coil terminal.
There's only one furnace but it looks like removing the electrode isn't all that difficult.
I'll get a new electrode when I have the board checked. Seems like the surest way.

I did find out that a meter lead on the coil and one to ground isn't how you test the ignitor  :p.

Update: so instead of driving an hour to town, thought I'd play with my new furnace knowledge.
Removed the burner assembly, spade clip on the electrode was bad so replaced it, terminal was really corroded so I gave it a good cleaning, reassembled and like magic I now have a working furnace.
I said all that to thank everyone that gave me help. And as usual, Gary lives up to being THE RV Wizard.
 
OK I'm going to jump in here and hopefully Gary can give me some help.
i have a 2012 keystone sprinter with a suburban furnace, when i turn it on at the thermostat, i hear a click at the thermostat and then a click where the furnace is and then zero, zip, nada.
model # sf-30FQ
 
i have a 2012 keystone sprinter with a suburban furnace, when i turn it on at the thermostat, i hear a click at the thermostat and then a click where the furnace is and then zero, zip, nada.
Click to expand...

The click at the furnace is the fan relay closing to start the fan, but apparently the fan isn't running. Nothing else can happen until the furnace fan reaches an adequate speed. At a guess, either the fan has failed or the fan relay (on the circuit board) did not actually deliver 12v power to the fan.

See my Furnace Troublehshooting document to understand how it works. Furnace Troubleshooting
 
Mine did the same thing and I found that the sail switch was stuck. Found the switch and worked it a few times and now all is good'
 
Mine did the same thing and I found that the sail switch was stuck.
Click to expand...

Not the same thing at all.  The sail switch does not come into play unless and until the fan starts blowing air.  The sail switch purpose is to stop ignition of the burner if the air flow is inadequate.  If the sail switch fixed yours, then your fan must have been running already.
 
Gary RV_Wizard said:
The click at the furnace is the fan relay closing to start the fan, but apparently the fan isn't running. Nothing else can happen until the furnace fan reaches an adequate speed. At a guess, either the fan has failed or the fan relay (on the circuit board) did not actually deliver 12v power to the fan.

See my Furnace Troublehshooting document to understand how it works. Furnace Troubleshooting
Click to expand...

Thank you very much Gary
 
texaslime said:
Mine did the same thing and I found that the sail switch was stuck. Found the switch and worked it a few times and now all is good'
Click to expand...

didnt mean to reply to this one
\
 
Rene T said:
You should start your own post.
Click to expand...

isnt this why we have a search button? as to not keep creating the same post over and over on the same topic? most forums hate it when there are multiple posts and encourage using the search button.
 
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