 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / RVs / October 2005RV Furnace Problem
My camping buddy has an intermittent problem with his Suburban furnace. Seems sometimes it runs beautifully - sometimes not at all - not even the fan. Other times the fan will start but the burner refuses to light (the igniter clicks so it probably is okay). Sometimes after running fine, the fan will not stop at the end of the heating cycle. It runs and runs. We have tried several thermostats - with same results. We have eliminated the thermostat and merely crossed its two wires - with same results. What is the most likely part failure? I have already put in a new 'sail switch' and it passes voltage just fine when 'on'. Thanks > My camping buddy has an intermittent problem with his Suburban > furnace. Seems sometimes it runs beautifully - sometimes not at all - [quoted text clipped - 11 lines] > > Thanks It could be on the control board. I had one, about a 1995 era, that when new would not work when the circuit board was cold!! When I took it to the shop where it was warm it worked great. The problem with it was that the igniter did not fire. The fan would come on and the gas valve would open for a short time but the igniter did not fire. If outside I could smell gas for a short time so I knew the valve was opening. I didn't listen for the igniter but assumed it was not working. I think that board was designed to try 3 times. Then it would quit trying but leave the fan running. I then found that I could warm up the board if I turned on the burners on the stove while the fan was running. Then turning the furnace off and back on caused it to try again and the furnace would light. After getting on a first name basis with the company they sent a new board. It had completely different components. No more problems. By any chance has he been able to smell gas when it is trying to light? >It could be on the control board. I had one, about a 1995 era, that when >new would not work when the circuit board was cold!! When I took it to the [quoted text clipped - 14 lines] > >By any chance has he been able to smell gas when it is trying to light? I feel the iginiter is working. I heard it clicking about five times a few seconds apart and would repeat that cycle if I turned the thermostat off and back on again. No I have not smelled any gas at all. Thanks > >It could be on the control board. I had one, about a 1995 era, that when > >new would not work when the circuit board was cold!! When I took it to the [quoted text clipped - 22 lines] > > Thanks Since you are listening to the igniter you must be close to the outlet and should very definitely smell gas. There are so many things that have to be working it gets really difficult to find. I suppose the problem could be low gas pressure, blocked burner, flame sensor or it could be that the board has a fault. Since it works much of the time I wonder if there could be an intermittent on the circuit board. If it were mine I might pull it out and go over all the joints with a soldering iron. A big job as you have to pull out the furnace. A "cold solder joint" can be really difficult to find. I have seen them where it took a magnifing glass to see them. >Since you are listening to the igniter you must be close to the outlet and >should very definitely smell gas. [quoted text clipped - 8 lines] >furnace. A "cold solder joint" can be really difficult to find. I have >seen them where it took a magnifing glass to see them. We actually did remove the furnace and bench-tested it with a separate propane hook-up, using wire extensions from the trailer wires themselves. It seemed to work great, but then sometimes it does in place. We are at a total loss. You probably are right about the board. We thought about buying one as a last resort, but they are expensive. Thanks Geezer > We actually did remove the furnace and bench-tested it with a separate > propane hook-up, using wire extensions from the trailer wires [quoted text clipped - 6 lines] > > Geezer Too bad, when you had it out it would have just taken a few minutes to go over all the solder joints with an iron. Maybe nothing wrong with the board. Just a little crack in the solder. I have seen many cold solder joints where a wire from something like a transistor is soldered to the board. Looking at it with a magnificing glass you see a tiny crack in the solder all around the wire. Just move the board a bit causing the wire to rub a clean spot and the fault will clear up for a while. However, in that case I would expect it to work for a while after you put it back. > We actually did remove the furnace and bench-tested it with a separate > propane hook-up, using wire extensions from the trailer wires > themselves. It seemed to work great, but then sometimes it does in > place. We are at a total loss. You probably are right about the > board. We thought about buying one as a last resort, but they are > expensive. My hunch is that there is a bad ground somewhere. Tricky things, they can look connected when they aren't.  SignatureJon JPinOH >My hunch is that there is a bad ground somewhere. Tricky things, they can >look connected when they aren't. I will check the ground this weekend and let ya know if I am successful. Thanks for helps. G >I will check the ground this weekend and let ya know if I am >successful. > >Thanks for helps. > >G Well guys - I checked. I checked all wires and all connections seemed okay. What we have done is this: 1) We found that if we simply crossed the two wires at the thermostat (red & white) the furnace runs fine - except that we must of course un-cross the wires to shut the furnace down because it gets pretty hot. 2) We tried a 'house' thermostats my friend bought at Home Depot (why I don't know - except it was cheap), but it did not work at all. 3) We tried a spare thermostat I had from my trailer that I know is good. It is different from his because mine handles both A/C and Heat using several wires. His only has two wires, as I said. My thermostat has its own ground wire, which I grounded. My thermostat behaved just like his, namely the furnace blower comes on, but the burner does not. 4) It bothered me that his white wire was the hot wire. I would have expected the hot wire to be the red one. We tried connecting his thermostat with wires reversed, but it did no good. Same result. 5) We installed a 12V toggle switch to eliminate his having to manually cross and un-cross the wires. It works the furnace just fine - except for the fact that he must be sure to turn the switch off and on himself. It really seems clear that the thermostat is the problem. But his seems merely mechanical and simple, so how can it be failing? It does 'trip' and stay 'tripped' when it should under temperature changes. Is there another part of the thermostat that I am missing? Thanks Geezer Sounds like you need to install a new, suitable thermostat. As to "suitable", here is a clip I took from http://yarchive.net/electr/thermostats.html There are two major variations - thermostats that are powered from the loop voltage and those that contain their own battery. Loop-powered thermostats will not work on millivolt (self-powered) furnaces. Such furnaces only supply about 700 millivolts to the thermostat circuit. If you don't know what kind of furnace you have and don't have a suitable meter, buy a digital thermostat that is battery powered and is rated for both 24 volt and millivolt circuits. Read the label. Even if an e-stat has an internal battery, if it is not rated for 700 mv service, it may not work. This is because relays not designed for low EMF switching can sometimes accumulate film on the contacts that the 700 mv cannot punch through. They work fine on the 24 volt systems. Relays rated for low EMF switching have high pressure contacts that will cut through the film even at low voltages. > Well guys - I checked. > [quoted text clipped - 28 lines] > > Geezer >Sounds like you need to install a new, suitable thermostat. As to >"suitable", here is a clip I took from [quoted text clipped - 14 lines] >for low EMF switching have high pressure contacts that will cut >through the film even at low voltages. Thanks for your interest. My friend's furnace and original thermostat are both Suburban. The furnace is a SF-35 (35000) - vintage 7 years or so. He is rather hard to help, and when I passed on your comments, and suggested that he buy a new thermostat (analog), he insisted that his creative on-off switch is quite sufficient, despite the fact that he must manually flip the switch to control the furnace's operation. I worry he will overheat the furnace, but it's like talking to a tree. I will continue to try. Thanks again Geezer. I am almost certain it is the control board. If you can need a new one I recommend going with a control board made by Dinosaur. They have several features that are vast improvements over the OEM boards. One of these is turning the fan off if the furnace doesn't light. The OEM board will just let the fan run forever or until the thermostat is reset. Not very convenient if your out of the RV. > > My camping buddy has an intermittent problem with his Suburban > > furnace. Seems sometimes it runs beautifully - sometimes not at all - [quoted text clipped - 30 lines] > > By any chance has he been able to smell gas when it is trying to light? SignatureMatt "Where are we going again, Dear?" > My camping buddy has an intermittent problem with his Suburban furnace. > Seems sometimes it runs beautifully - sometimes not at all - not even the > fan. Other times the fan will start but the burner refuses to light (the > igniter clicks so it probably is okay). Sometimes after running fine, the > fan will not stop at the end of the heating cycle. It runs and runs. I've got to say- this sounds like a power problem. There is no one part which would cause all of these problems- other than the thermostat (unless the furnace is new enough to have a "fan control" circuit board- which would be in the last year or so, and still under warranty). Of course, it could be a few problems in one- for the blower not coming on, the only parts in the circuit are the thermostat (already eliminated), the fan relay (a good possibility) and the fan motor itself. For the flame not igniting, it could be any of the above (by not letting the fan get up to speed), or the sail switch, hi limit switch, ignitor board or an LP problem. But... I would start with all of the power connections to the furnace- a bad connection could do all of the above- not let the blower start, let the blower start but not fire the ignitor, or let the thing work fine. Make sure to check the grounds as well, though usually they are not a problem, given the ground through the copper LP line. SignatureChris Bryant http://bryantrv.com
|
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.