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Old 05-05-2015, 02:24 PM   #1
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problems with furnace

I have a 1996 casita witha NT12SE suburban furnace that won't light. Have used Harry Young's majic trouble shooting guide that helped greatly. It has come down to everything working except no gas. Have no power to the solinoids on the electric gas valve. The manuel switch is fine. Is Harry still out there or is anyone familier with this problem? thanks Eric
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Old 05-05-2015, 05:35 PM   #2
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Originally Posted by sorceress View Post
I have a 1996 casita witha NT12SE suburban furnace that won't light. Have used Harry Young's majic trouble shooting guide that helped greatly. It has come down to everything working except no gas. Have no power to the solinoids on the electric gas valve. The manuel switch is fine. Is Harry still out there or is anyone familier with this problem? thanks Eric
I once had a problem with a gas top range because the RV's battery was almost dead.

Just a thought...

Bill
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Old 05-05-2015, 06:08 PM   #3
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furnace problems

Thanks Bill, already have it out and apart, it's being bench tested with a 12 volt power supply, thanks again.Eric
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Old 05-05-2015, 09:46 PM   #4
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4 things have to happen before the furnace will attempt to light.

Furnace switch has to be on and temperature has to be below shut off point by at least a few degrees so a demand for heat is activated.
Battery voltage has to be right.
Fan has to be up to speed. Fan air flow switch has to activate. To release propane from the safety switch.

Propane has to be on and and at the pressure safety switch. Light the stove, both burners and check them on highest setting.
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Old 05-05-2015, 09:49 PM   #5
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Did you put a jumper across the thermostat in case those contacts are bad?

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Old 05-05-2015, 10:55 PM   #6
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Other than no propane, the common problems listed the one that trumps all others is the Sail Switch. Either from being gummed up, from switch failure or from inadequate airflow.
For starters, try starting the furnace several times while connected to the TV's charging line. It's voltage is usually higher than battery or charger and will spin the fan faster. On some models you can reach in with a wire with a hood on the end and manually pull the sail forward to trip the switch Last is jumping the switch to test and then replacing it when the furnace fires off..


I never look at any of the other problems before ruling out the sail switch



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Old 05-06-2015, 12:25 PM   #7
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4 things have to happen before the furnace will attempt to light.

Furnace switch has to be on and temperature has to be below shut off point by at least a few degrees so a demand for heat is activated.
Battery voltage has to be right.
Fan has to be up to speed. Fan air flow switch has to activate. To release propane from the safety switch.

Propane has to be on and and at the pressure safety switch. Light the stove, both burners and check them on highest setting.
, Thanks Steve, I have the unit out on the bench. Using a 12 volt power supply, hooked up to propane with reg. The sail switch and the gas switch are OK. When I try and fire it up, fan kicks on, sail switch moves but get strange sporadic voltages that don't hold, at the gas switch, low voltage. is there anyay to jump the soliniods to see if it fires up? thanks Eric
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Old 05-06-2015, 02:57 PM   #8
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Probably the contacts in the sail switch. Easy to replace since you've got it on the bench - I had to do the same thing in another Suburban furnace.

You can take the wires off the sail switch and jumper them directly to 12V and see if the solenoid stays open.

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Old 05-06-2015, 04:46 PM   #9
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thanks Charlie, I used a continuity tester on the sail switch, shuts on and off fine, but I haven't put 12 volts to the two wires. Will try that. Can I jump the solinoids on the valve with 12 volts? can't seem to find out what voltage they are. Also they seem grounded to the chasis when not in use. Also will the solinoids make an audible click when the open?Thanks again.Eric
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Old 05-06-2015, 06:12 PM   #10
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thanks Charlie, I used a continuity tester on the sail switch, shuts on and off fine, but I haven't put 12 volts to the two wires. Will try that. Can I jump the solinoids on the valve with 12 volts? can't seem to find out what voltage they are. Also they seem grounded to the chasis when not in use. Also will the solinoids make an audible click when the open?Thanks again.Eric
I don't recall the solenoid making an audible click. I was bench testing to see how low the voltage could go and still run the furnace when I did a lot of winter camping on mountains during ski season. Think it was down around 10.5 volts and the furnace would still run.

One side of the solenoid should be grounded, but the other should read a few ohms (the coil resistance) unless the solenoid itself is shorted - which can happen. But then you should blow a fuse...........
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Old 05-06-2015, 08:34 PM   #11
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Here is at troubleshooting sequence to go through to check what's working and what isn't working. Sounds like it may be the gas valve or dirty orifice , but I hope this info helps



http://bryantrv.com/docs2/docs/suburban_dd_nt.pdf
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Old 05-06-2015, 08:37 PM   #12
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Should've mentioned that it the info is on page 14

Take care
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Old 05-08-2015, 02:45 PM   #13
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Thanks, i'm going to go through nthe check list in a few days, will let you guy's know. I realy appreciate the help.Eric
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Old 05-17-2015, 11:32 AM   #14
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Here is at troubleshooting sequence to go through to check what's working and what isn't working. Sounds like it may be the gas valve or dirty orifice , but I hope this info helps



http://bryantrv.com/docs2/docs/suburban_dd_nt.pdf
Hi, finally got to go through the troubleshooting guid, Got to the valves and one had 12 volts, the other was all over the place in voltages. The valves were marked + and - so I jumped them and turned it on. When I jumped the rear one it clicked, but unit did not cycle, when I jumped the front one, same thing. So what I figure is board is bad, not supplying enough current to click on the electric valves.what do you think? thanks Eric
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Old 05-17-2015, 01:28 PM   #15
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From the schematic you have redundant gas valves wired in parallel. There should be 12V DC at both valves in order to get gas to the burner . Since both valves are fed from a common feed from the control board ,there must be a reason why one valve has 12 V and the other valve does not . The problem may be on the NEG or ground side of the valves. Are you getting spark from the igniter ?
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Old 05-17-2015, 02:51 PM   #16
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Hi, finally got to go through the troubleshooting guid, Got to the valves and one had 12 volts, the other was all over the place in voltages. The valves were marked + and - so I jumped them and turned it on. When I jumped the rear one it clicked, but unit did not cycle, when I jumped the front one, same thing. So what I figure is board is bad, not supplying enough current to click on the electric valves.what do you think? thanks Eric
Ignitors work fine. Don't think I'm getting enough current to trip solinoids? advise welcome. thanks Eric
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Old 05-17-2015, 02:52 PM   #17
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Going waaaay back, did you try jumpering the leads on the sail switch? Just because you show continuity doesn't necessarily mean that it can carry the current needed across it's contacts.


You mentioned that the 12 Volt reading at the solenoid was a bit flakey. Humor me and try jumping the sail switch leads. That switch probably provides more problems than all other problems combined.



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Old 05-17-2015, 02:54 PM   #18
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You might check continuity through your flame sensor , if flame sensor and sail switch have continuity , then I am afraid your board is the problem . Easy to fix but expensive .
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Old 05-17-2015, 03:28 PM   #19
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Sail Switch

Quote:
Originally Posted by Bob Miller View Post
Going waaaay back, did you try jumpering the leads on the sail switch? Just because you show continuity doesn't necessarily mean that it can carry the current needed across it's contacts.


You mentioned that the 12 Volt reading at the solenoid was a bit flakey. Humor me and try jumping the sail switch leads. That switch probably provides more problems than all other problems combined.
The sail switch is in series with the limit which in turn supply power to the control module. If the sail switch was not closing there would not be any power at the control module to power the ignitor or the gas valves .Since the ignitor is working and there is power to the gas valves it appears the sail switch is closing ,whether the contact in the sail switch is good is another question. Jumpering out the sail switch would eliminate that part of the circuit as the source of the problem. If the sail switch contact has high resistance ,you may not be getting full voltage to the control module ,gas valves and the ignitor especially under load . Low voltage systems are very sensitive to voltage drop across relay and switch contacts .
Solenoid have 2 different currents -pull in and hold. It takes more current to pull in a solenoid and less current to hold it in the energized position
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Old 05-18-2015, 02:07 PM   #20
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furnace problems

Well I tried that,didn't make any diference. rechecked and it is fireing, it seems the solinoids come on for a second or 2 then shut off. I can feel them click in, but they don't stay on long enough to get propane maybe. Anyway thanks again, is the timer for the solinoid in the board? thanks Eric
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