RV Repair: Suburban Limit Switch repacement, lp gas furnace, limit switch

Question
Bill,
We have a 1994 Winnebago motorhome that has a Suburban SF-42 LP Gas furnace. We started having trouble with it last fall. It wouldn't light. The fan would run but there was no ignition. Early this year after doing some research and some troubleshooting I decided that the igniter board was bad. I got one of the late igniter boards (Fan 50 Plus) and replaced it. It worked fine every time I tested it until we took a trip with it the last week of March. I had the same trouble sometimes. I tested some of the wires for voltage and discovered that there was very low voltage on the wire that came from the limit switch. I know it probably wasn't the best thing to do but I jumpered the wires that ran to it! The furnace worked and we used it for the remainder of our trip. But now I think I should replace the limit switch. I know it might just be a bad connection but the switch is only a few bucks. I assume I have to remove the furnace to get at it! My question is about getting the furnace out to do the job. As you probably know this furnace has a cover on the outside and will slide out. I know I have to disconnect the wires and the gas line but how do the ducts connect? Do I have to disconnect them or do I just slide it away from them? Thanks for your advice! David

Answer
Hi David:
Have seen poor limit switch voltage often. The limit switch sits at the rear of the furnace and should be accessible by taking the rear furnace cover off if you can get to it. If you have to take the furnace out the ducts just twist off conterclockwise. What comes off the furnace body is the round cover that the duct slips over. They come off easy but putting them back on is a pain. The furnace must have been replaced at some point as the "Fan 50 Plus" boards are only a few years old. Be carefull, bad things can happen if you run the furnace with the limit switch is bypassed.
Bill