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Car Forum / Driving, Maintenance, Tuning / RVs / September 2006Suburban NT-34L 12volt RV furnace won't ignite gas?
Well this isn't an 'easy answer'... going to take some real head scratching. I have significant electonics background so I have thoroughly checked everything electronic that i can as I have the original troubleshooting guide and the wiring diagram. Here's the stages it performs: 1. When thermostat triggers blue line, fans turn on instantly, creating airflow. 2. I assume sail switch and overtemp limit switch is working because before long, the module board consistantly tells the electrode to start sparking. 3. here's the problem: GAS DOES NOT IGNITE. I do not smell gas out the exhaust ports. So where is the actual failure? I don't see any gnats in the oriface, I see 12volts reliably at the gas valve. I have disassembled the gas valve a few times and reassembled. What's strange is this 'dissasemble, reassemble' of the gas valve seems to make the furnace work again so I put it back in thinking I 'fixed the valve' and it will work for a day and by about 2am when we need the heat on some trip, we are freezing again and it flat will again (like above description) start sparking every time, but no ignition. I am considering swapping the gas valve but before spending $122 for one, I wanted to run this whole thing by anyone that has had SPARK, BUT NO IGNITION. I have seen a lot of discussion on the internet about no spark and I dont want to flood the internet with that conversation again, because that's not my problem. If I'm clear to the spark step, I truely believe, unless an expert tells me otherwise, that my control board is good. Thanks for your help everyone! ~Brendan Jumping in like I was an expert/ My water heater suddenly quit with about the same symptoms. Spark, plenty of juice, but didn/t light and no smell of gas. My brother jumped to the rescue. Checked the relay and it was opening, He then disassembled the connection bring the gas from the tank Could not see trhough it so blew it out with air compressor disloging a speck of dirt almost too small to see. All started working again. Now that I typed all that, consider this. How full is your propane tank? Anne > Well this isn't an 'easy answer'... going to take some real head > scratching. [quoted text clipped - 39 lines] > Thanks for your help everyone! > ~Brendan Solutions:: I had a portable radio receiver that I used with a cigarette plug 12 volt that could be set for 6 volts. Suddenly the darn thing quit, so I ran to Radio Shack and bought another one. The outlet of the plug registered OK 6 volts, using a meter with 2 wires attached. A week later the new radio quit. Same thing the outlet registerd 6 volts. Later I was reading the instructions for the radio and it mentioned that the cigarette plug should have a certain diameter (outside). Aha. Maybe mine was the wrong size, so I bought another one with replaceable plugs on the end, picked the one that said it was the same size as my radio needed. Lo and behold, both of them now work fine. My guess is that I was not getting a really good connection. Moral of this tale. Just cause the meter says there is 6 volts doesn't mean that 6 volts are getting into the radio. Anne WildIrish wrote: If I'm clear to the spark step, I truely believe, unless > an expert > tells me otherwise, that my control board is good. > > Thanks for your help everyone! > ~Brendan I had a similar problem last fall and had other electrical problems following a nearby lightning strike so I stopped at the Winnebago factory. They took the furnace out and cleaned it. It worked okay through several cycles and then failed again. They swapped the circuit board and it has been fine since then. The labor cost and the board was more than a new furnace would have cost. LZ You didn't mention how old this furnace is. I had almost the exact same thing happen to a 20+ year old Hydroflame furnace. The problem turned out to be a decomposing rubber button on the solenoid plunger. It would stick closed strongly enough that the solenoid could not pull it up. I could make it open by rapping on the solenoid during the ignition cycle. I screwed around with it a bit, managing to make it stick open (interesting experience) before biting the bullet and replacing it. Problem fixed. John >Well this isn't an 'easy answer'... going to take some real head >scratching. [quoted text clipped - 24 lines] >again >(like above description) start sparking every time, but no ignition. --- John De Armond See my website for my current email address http://www.neon-john.com Cleveland, Occupied TN Don't let your schooling interfere with your education-Mark Twain >... decomposing rubber button on > the solenoid plunger. It would stick closed strongly enough that the > solenoid could not pull it up. I could make it open by rapping on the > solenoid during the ignition cycle. I assume you are referrring to the rubber diaphgrams inside the gas valve? I have had it appart and back together a number of times, and it will work fine afterwords for a period, and then fail again... maybe sticking like your is but would never stick when I was bench testing. I smell no gas so I really think I have no gas through that valve. Hey does anyone have any easy suggestion on how to test for proper pressure with 'common household items' or with a simple pressure gauge? I have talked to a few gas supply companies and none of them seem to have pressure gauges....... ?? strange if you ask me. -Brendan > gauge? I have talked to a few gas supply companies and none of them > seem to have pressure gauges....... ?? strange if you ask me. Strange if you ask me, too. Stranger still, Froogle doesn't have much to offer if you search for lp gauge. http://www.skymall.com/shopping/detail.htm?pid=69747336 looks like it will give you a general idea of your pressure level. You could probably adapt it to attach in-line at a location that's remote from the tank (maybe near your furnace). I don't know if such an adaptation is a safe idea. Froogling for propane gauge offers some regulators with built-in gauges...not really what you're looking for either. >> gauge? I have talked to a few gas supply companies and none of them >> seem to have pressure gauges....... ?? strange if you ask me. > >Strange if you ask me, too. Stranger still, Froogle doesn't have much >to offer if you search for lp gauge. That's because an LP gauge isn't what he's looking for. The cheap DIY method is the water U-tube manometer that I described elsewhere in this thread. If he really wants a gauge with a dial and pointer on it then limber up that wallet. A low pressure gas gauge - what the device is called - starts at about $50 and goes up rapidly, depending on the dial size and accuracy spec. >http://www.skymall.com/shopping/detail.htm?pid=69747336 looks like it >will give you a general idea of your pressure level. You could probably >adapt it to attach in-line at a location that's remote from the tank >(maybe near your furnace). I don't know if such an adaptation is a safe >idea. That is a high pressure tank pressure gauge and has nothing to do with the low pressure gas downstream of the regulator. That gauge is perfectly worthless for its intended purpose. The high pressure varies only with temperature until all the liquid propane in the tank has evaporated. Then it drops like a lead brick. IOW, that gauge will confirm that you're out of propane. Not sorta out but plum out. John --- John De Armond See my website for my current email address http://www.neon-john.com Cleveland, Occupied TN Don't let your schooling interfere with your education-Mark Twain > On 12 Sep 2006 14:20:34 -0700, "Rick Onanian" wrote > >Strange if you ask me, too. Stranger still, Froogle doesn't have much > >to offer if you search for lp gauge. > > That's because an LP gauge isn't what he's looking for. The cheap DIY > >http://www.skymall.com/shopping/detail.htm?pid=69747336 looks like it > > That is a high pressure tank pressure gauge and has nothing to do with > the low pressure gas downstream of the regulator. That gauge is > perfectly worthless for its intended purpose. The high pressure I knew you'd have the answers, and almost wrote "Neon John would know". If I had, instead of writing what I did, I wouldn't have learned. Thanks! > >... decomposing rubber button on > > I smell no gas so I really think I have no gas through that valve. There should be a manual shutoff valve on the gas line leading to the furnace. Turn it.  SignatureJon JPinOH Hi! I haven't read all the replies so someone probably suggested this. Is there a thermocouple near the pilot? Every gas furnance that gave me this problem was either thermocouple or insects. Al >>>... decomposing rubber button on >> >>I smell no gas so I really think I have no gas through that valve. > > There should be a manual shutoff valve on the gas line leading to the > furnace. Turn it. My valve had a round steel plunger in the solenoid valve that was tipped with a little rubber biscuit. This biscuit mated to the valve's orifice so that when the plunger was released, the orifice was closed and no gas flowed. This biscuit had gotten soft so that it would stick to the sharp edge of the orifice. To measure gas pressure. Get a length of clear plastic tubing, say, 3/8 or 1/4" - doesn't matter. Shape it in a "U" and tape it to a yard stick so that the U is at the bottom and the open ends are at the top. Fill about half full with water. Add a drop or two of food coloring if you wish to make the water more visible. A tiny drop of dishwashing detergent added to the water will flatten the meniscus (the water line) and make it easier to read. This is a U-tube manometer. Leave one end open and apply gas pressure to the other. The DIFFERENCE in the levels is the pressure. It should be 11" of water for propane. One leg should rise about 5.5 inches and the other sink the same amount. John >>... decomposing rubber button on >> the solenoid plunger. It would stick closed strongly enough that the [quoted text clipped - 15 lines] > >-Brendan --- John De Armond See my website for my current email address http://www.neon-john.com Cleveland, Occupied TN Don't let your schooling interfere with your education-Mark Twain > Well this isn't an 'easy answer'... going to take some real head > scratching. [quoted text clipped - 39 lines] > Thanks for your help everyone! > ~Brendan Obviously it is the gas valve or associated circuit. I think think the circuit is such that after three tries to ignite it give up. I had a problem once of no spark and I could smell the gas for a short period of time before it gave up. That was a new unit. Wouldn't spark when the circuit board was cold!! Worked fine when warm. Anyway that was fixed under warranty. They sent a new board that was a complete new design. The components were entirely different. > Well this isn't an 'easy answer'... going to take some real head > scratching. [quoted text clipped - 39 lines] > Thanks for your help everyone! > ~Brendan I occasionally have this problem when I first light up for the season. What I do to remedy it is light my stove burner first this ensures that gas is traveling to appliances, my hot H2O tank is near the stove so, once it lights I know A. there is gas, the valve has opened and if I attempt to light the hot water heater and furnace it will no light on the 2nd or 3rd electronic ignition (keep quiet and listen for click). Ed |
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