Its an old beauty. Did Singer get out of the A/C business. I can't get any info(Wiring Diagrahm)on these hogs. All I can tell is its a 1978 Package unit. 2 1/2 ton AC and 100,000 btuh input nat gas.
Problem was a bad T-stat, but noticed power vent motor on all the time even in cooling mode.Looks like somebody replaced it recently. No power to W terminal.