Performed diagnostic on a 2018 Coleman furnace. Upon arrival found system was non operational, plugged pressure switch hoses, unclogged all hoses. Test heater system and has a 13 degrees temperature rise. Adjusted blower speed from high to med, temperature rise improve to 18 degrees. Gas pressure at 12 coming in and 10 out. Found incorrect orrifices size at 54, tech support confirm it should be 55. Suggest replacing propane kit at this point to diagnose further. Give estimate for repair.