LaMonte,
"Kneejerk" reaction is a faulty t'stat, switching to fan only. Not sure how yours is wired but if you have a fan output on the t'stat, disconnect it when unit is acting up. If fan stops, almost has to be the stat. Better yet, take voltage readings on t'stat outputs when unit is operating normally, then again when it is acting up. If reading are the same t'stat is probably OK.
Steve