I connected up the wiring from the thermostat and powered up the furnace. Taped interlock switch for the front panel. After studying the wiring diagram I realized that part of the LP conversion kit there is pressure switch added to the furnace so it won't turn on with no gas pressure. I connected up my 20lb gas tank to the furnace to see if it would start and it did.
I only momentarily let the furnace run not knowing if the gas pressure from a 20 lb gas tank would have enough gas pressure (or to little) to fire the furnace.
Question: For testing purposes-- can I run the furnace on a 20lb tank? Should I have a regulator on it?
I think (but am not sure) that you can or maybe already have damaged things in the furnace without having a pressure regulator in line. Now, the furnace itself may have a secondary one and you may be lucky. Typically, there's a regulator on the LP tank before it feeds anything. WIth a bare 20# tank, that is missing.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013