A common culprit to an improperly functioning Suburban furnace is your sail switch. In order to determine if your sail switch is getting the proper power, let's run through how to bench test it.
1. Make sure you have proper voltage coming into your furnace. Use a multimeter to determine that you are getting the appropriate DC flow.
2. Next, ground your negative on your multimeter to a negative batter line and then connect the positive on your multimeter to the positive line entering your gas valve.
3. Now using a test light, attach your ground to the grounding block on the furnace itself and attach the light to the red wire going into the sail switch.
4. Turn your furnace on.
Voila! If your light turns on, your sail switch is functioning. If not, this is likely your issue if your furnace is not operating properly.