billkoboldt Report post Posted January 1, 2013 I have had a problem with my furnace in a 2003 class A Coachmen. If the weather is 25 degrees or colder the furnace will not ignite, nor will the fan start. The batteries are fully charged and it is plugged into shore power. The other day I put a small electric heater about 8 inches away from the air vent inside the coach and turned it on high for about 15 minutes and then it started. Anybody out there know what the problem could be. I have no problem with it during cool mornings in the spring or fall. Thanks for any help. Share this post Link to post Share on other sites
wolfe10 Report post Posted January 2, 2013 Since the fan does not even come on, and that is the first step in the "light the furnace" process, my first suspect is an electrical issue. Start by checking that all connections are tight. Remember, when cold, metal SHRINKS and can make a marginal connection inoperative. So, connections at thermostat and at furnace (outside access door). If that does not do it, unplug the connection on the furnace PC board (outside access door) and clean with DeOxit or other good electrical cleaner. Share this post Link to post Share on other sites
RVerOnTheMove Report post Posted January 2, 2013 In order for the furnace to ignite the fan must run first. There is a "sail switch" that must sense air flow first before anything else will happen. As mentioned above, the heat is effecting something in the loop so you might want to check that something that is closest to your heat source. Is the heater making it warmer where the thermostat is located? Where the fan is located? Where a circuit board might be located? Once it's warm and running, does it keep running "forever"? Any additional details you can think of? Share this post Link to post Share on other sites
dickandlois Report post Posted January 2, 2013 Do you have the owners manual for your furnace? If not list the Make an Model number and I will see if I can supply a cope of some information that covers you's. Rich. Share this post Link to post Share on other sites
billkoboldt Report post Posted January 2, 2013 After putting an electric heater in front of the inside vent yesterday, today with outside temp of 20 degrees, the furnace started right up with no problem. No electric heater needed this time. Yes, it will start up after it initially get it running. It is an Atwood hydro flame furnace, 8900-III series. The owners manual does not have any trouble shooting information in it. Thanks for all the information from everyone. Bill. Share this post Link to post Share on other sites
dickandlois Report post Posted January 2, 2013 Bill, This information may fill in some of the gaps in your information. Link. http://www.atwoodmobile.com/manuals/furnaces/MPD%2032046%20E%2011.27.06.pdf Rich. Share this post Link to post Share on other sites
WJS822 Report post Posted January 3, 2013 I have a related issue, 06 H/R Endeavor, 5 button thermostat, when trying to run the front furnace it doesn't show on the thermostat. The back one shows up as you are scrolling through the menu. Would it be a bad connection the reason it is not showing on the thermostat? Share this post Link to post Share on other sites
baynhambecky Report post Posted November 30, 2013 Atwood 8500 Hydro Flame Furnace. Fan comes on, cycles and goes off. Replaced electronic board as suggested. Still the same symtom, fan on, cycles, fan off. Any suggestions or help out there. Thanks so much Ed Share this post Link to post Share on other sites
wolfe10 Report post Posted November 30, 2013 Ed, Welcome to the FMCA Forum. Actually the board would NOT be one if the first things I would suspect with your symptoms. You have a SAIL SWITCH that closes when it senses adequate air flow. If that doesn't happen, there will be no gas valve opening or ignition sparking. Causes of sail switch not closing: Low voltage at the furnace causing the fan speed to be too low. Restriction in air return causing restricted air flow. Restriction from crushed air duct and/or closed heater vents. Share this post Link to post Share on other sites
tbutler Report post Posted November 30, 2013 Or the sail switch itself could be faulty. We had one quit several years ago. Replacing it solved the problem. On our furnace the switch is easily located on the fan housing and it is an easy replacement. Try Brett's list and it that doesn't get it, order a new switch. Share this post Link to post Share on other sites
wolfe10 Report post Posted November 30, 2013 Tom is absolutely correct. But a lot of PC boards and sail switch have been replaced that were perfectly good. Go through all the diagnostics rather than throwing parts at it. A loose or corroded connection where 12 VDC does into the furnace or a duct in the basement crushed by a box can cause the same symptoms as a PC board. Share this post Link to post Share on other sites
baynhambecky Report post Posted December 3, 2013 Brett and Tbutler, thanks for the info. Trying not to throw parts at it but the board was bad when it was taken out and tested, so replaced it. Now I know what to do next. Thanks. Thanks Share this post Link to post Share on other sites
