Originally posted by Hroper Blow the fuse before you replaced the T-stat?
Yes, actually. The unit is for the daylight basement, and as such, used infrequently (never gets too hot down there). We went to run it for a while to give it some exercise and noticed it wouldn't come on. That's when we discovered the blown 3A fuse.
From there it was trial and error, and today I think I'll order the replacement contactor from McMaster-Carr based on the help I've received here.
EDIT: I got the replacement contactor today and installed it. A/C runs like a champ, thanks to all who helped out.