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Old 02-21-2004, 04:00 PM   #1
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Furnace Broke

Hi,

I have a furnace that stopped working and the thermostat contacts show there's no voltage across them. So I thought it could be a fuse but the fuses on the interior panel looked ok. Cycled all the breakers on the panel next to the fuse panel. Could there be more fuses to check in another location? It's a 92 Airstream Landyacht MH 30'. Don't know what brand of furnace it is. Or does anyone know what else to check?

Thanks for any help.
Dave
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Old 02-21-2004, 05:53 PM   #2
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Check at the furnace to see if there is voltage to it, you will know if it is the wiring or the furnace.

John
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Old 02-21-2004, 06:41 PM   #3
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At your furnace, check to see that one of the blue wires (there are 2) has voltage. The blue wires from your furnace go to the thermostat, and when they are connected that means that your thermostat is calling for heat.

If there is voltage to the 2nd blue wire, then check for voltage at the gas valve solenoid. If there is no voltage there, check for voltage on both sides of your sail switch.

Also check for a spark at the igniter; they do corrode.

If you have voltage at the sail switch, and no voltage at the gas solenoid, then the circuit board is suspect.

If that is the case, then believe me, it is cheaper to buy a new furnace than get caught in the clutches of an RV dealership.

Find a new circuit board on the net.
Dick
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Old 02-21-2004, 07:05 PM   #4
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I hope it's not the circuit board.

Thanks for the things to check. Will go down tomorrow and see if I have DC anywhere else.

Dave
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Old 02-21-2004, 09:00 PM   #5
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I think I have the same problem. I was trying to figure it out today. I too will check these things tomorrow.
Thanks for the tips.

Don
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Old 03-09-2004, 11:57 AM   #6
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In case anybody's following this thread, I finally got around to prepping my camper and looked into the furnace prob again.

Found the problem. The thermostat finally gave out. That explains why it worked for a while then stopped working on a cold night. The RV must've sat for several months to a year before I finally bought it.....and started using the furnace again.

I'm going to stop by Home Depot and see if I can find one that is close to the same size.

So if anyone else is still having problems, I'd suggest checking the continuity of the thermostat/switch too.

Happy Camping
Dave
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Old 03-11-2004, 07:33 PM   #7
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Thanks Dave, I haven't had time to check and fix mine, but need to soon, as it's getting time to start traveling !!!
Don
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Old 03-11-2004, 08:25 PM   #8
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Dave,
I would be interested to learn if a house type thermostat will work for a trailer type. I believe that a house type is 24 or 32V AC, and 12V DC would fry the contacts, IMHO.
Dick
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Old 03-11-2004, 08:30 PM   #9
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Home AC units use DC to run most thermostats and the DC closes the High Voltage relays that then start the motors. If the unit is a home one you just need to get a simple unit that is not heat pump compatible. Heat pumps add some additional stuff.

Inside your AC or heat at home somewhere is an AC to DC transformer. This means the wall control less expensive to make and the low voltage wire is easy and cheap to run.
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Old 03-13-2004, 01:25 PM   #10
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Just got back from a 4 day trip and found out that the electronic thermostat that I bought didn't work. (I gambled). It's a small digital dial made by Honeywell that can work with multiple types of house systems. The unit gets its power from the thermostat wires. There's just two wires needed in a house that uses the 10-volt transformer in line with the thermostat.

In my MH, the two wires are delivering 12V DC to the thermostat and when the contacts close in the thermostat (calling for heat), you can see where that's going, right? The thermostat unit loses it's power supply, and it goes into a cycle where the furnace starts and stops over and over again.

I gave up trying to figure a way to make it work in a DC system. The contacts (electronic) inside the thermostat unit must allow one half-cycle of the 60 HZ AC to power the unit while the opposite half-cycle is shorted out, (acting like a switch)...maybe.

I needed a digital thermostat at home anyway to replace the old mechanical one so the one I bought should work at home.

I'm going to shop around for a another digital thermostat for the MH and see if I can make one of the battery powered digitals work...because I want a digital thermostat now. Honeywell makes a reliable mercury type, but having a digital makes it much nicer because I can set the number on it and not have to experiment to get a good temperature.

I'll let you know what type and how it works when I'm done.

Dave
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Old 03-13-2004, 01:34 PM   #11
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Quote:
Originally posted by Navigator
Dave,
I would be interested to learn if a house type thermostat will work for a trailer type. I believe that a house type is 24 or 32V AC, and 12V DC would fry the contacts, IMHO.
Dick
I think that the household types will work in the RV as long as they run off of batteries. The other comment I just posted explains what happened with a household type that needs power from the thermostat wires. Household thermostat wires carry AC from a small transformer near the furnace in systems that I've seen.

But any type of thermostat that doesn't need power for its own circuits (like a mercury type) should work.
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Old 03-17-2004, 11:45 PM   #12
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Just bought another thermostat and this one works in the RV and is digital. What makes this one work is that it uses 2 AA batteries instead of getting power from the thermostat wires.

For about $50 from OSH I found one that has Air-Conditioning and Fan-Only switches (which I can't make use of them), so it's a little wasteful. But there weren't any other types available that use batteries instead of thermostat current. So, for the money, it's well worth it to me to be able to have a digital thermometer and control.

Finally, this closes the chapter on *my* furnace problem. Now, will have to wait until it gets cold again at night so I can use it. I hope the 2 AA batteries last all summer...in order to keep the little clock going.

Dave

P.S. I guess summer is already here in California. Lived in the Bay Area for almost 35 years and I don't recall seeing such a warm spring-time ever that has had clear days for over 2 weeks without cooling off. Could it be the due to global warming?
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Old 03-18-2004, 10:40 AM   #13
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Since the Forum becoming very mature, don't forget to search the archives!

From deep in the archives - Digital Thermostat
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Old 03-18-2004, 11:19 AM   #14
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Quote:
Originally posted by 1985air345
Since the Forum becoming very mature, don't forget to search the archives!

From deep in the archives - Digital Thermostat
Well...now that I've already been through the whole process, I guess that older thread isn't much help to me any more. But I can see that others have dealt with the exact same issues I've been dealing with. Wish I would've searched it earlier but this thread changed from a furnace problem to a report on how one furnace problem was solved.

Dave
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