Furnace troubleshooting

[davidmurphy02]

I've been through several problems with the furnace in our 2019 5.0TA and in the process have learned a lot about how the furnace works, troubleshooting steps, and found some good resource information so I thought I'd share that here for others who may have furnace problems down the road.

Sometime in 2018 Escape started using a furnace with a large exterior door that allows easy access to most of the components. Prior to that many repairs required removing the furnace from inside the trailer, so if you have a later model trailer with the outside door consider yourself lucky.

If your furnace doesn't work - runs briefly and then stops - the first thing to do is to check the flashing light on the circuit board. That means removing the four screws holding the exterior door in place. The circuit board will be visible and will have an LED flashing - either repeating one, two or three flashes or staying on constantly. Nearby on the black plastic blower motor housing there will be a sticker with the trouble codes that tells you what the different flashes mean, and that will give you an indication of what the problem is.

When the furnace is activated by the thermostat, first the blower turns on. The circuit board gets a signal from both the sail switch and high limit switch that all is well, this takes about 15 seconds. Then it opens the gas valve and activates the igniter to light the burner. If the burner doesn't light within 5 seconds it stops and the blower will continue to run to blow out any unburned propane. 15 seconds later it will try the ignition process again. It will make three attempts at ignition, and if all three fail it will shut down.

The easiest way to quickly identify the nature of a furnace problem is to turn on the furnace and then run outside and listen at the exhaust vent. If there is a sail switch problem the blower will run for 30 seconds or so then stop and you won't hear the igniter fire. If the sail switch is OK, you'll hear a rapid clicking noise as the igniter fires. When the burner lights it makes a noticiable whooshing sound and you'll feel hot air coming out the exhaust. If the burner doesn't light, it will make two more attempts at ignition when you'll hear the clicking sound of the igniter.

If your blower only runs 30 seconds or so and the igniter never clicks and fires, you probably have a sail switch problem. The sail switch has a spring loaded arm with a small flat metal "sail". When the blower is running, it moves the sail switch and closes a contact point which tells the circuit board that the air flow is OK. Without that signal the furnace will not attempt to ignite. People have often reported finding hair, fuzz, and other debris in the sail switch that may have prevented it from closing and that by removing it and blowing it off and cleaning it, it began working again. However, it's common when that happens to have that recur and you can wind up cleaning the sail switch frequently. My opinion, based only on my own experience, is that the sail switch is a poorly manufactured component that is subject to a high failure rate. After cleaning mine several times I replaced it with a new one which has worked flawlessly without intervention for almost two years now. So my recommendation is to purchase and carry a spare sail switch. If your sail switch malfunctions while on the road, it's worth removing and cleaning it, often that will get it working again for a while.

In the photo below the screwdriver is pointing at the sail switch. It mounts on a black plastic block and the long part of the switch goes inside the blower motor housing in the airflow. Above the sail switch is the circuit board - you can see the LED sticking up near the lower right corner, this is what will flash repeatedly with an error code if you have a problem. And directly below the sail switch is the sticker that tells you what the error codes indicate.