There is a sticker on the inside of the lower panel that will describe what each of the flashing lights (whether green, amber, or red) means. Green is good. Amber and red will likely require a heating professional to address the problem.
U.S.A.C.D
This is the same as the limit switch, just a second one it is still a normally closed circuit that opens at whatever predetermined set point
yes they are. they both made by york international. luxaire would be considered a premium line. york of course is there ultimate premiere line. guardian and a line called evcon were considered to be more of a builder model.....i never sold too many of the evcon or guardian myself.