I replaced the older Sears HVAC thermostat the other evening. It's wired up as a 4-wire, with a jumper between Rc and Rh. The sheath containing the 'stat wires is labeled "Type 5", so I'm assuming it used to be a 5-wire; I've found a 5th blue wire that someone cut off, and it's not connected to anything in the old thermostat.
I installed a new Honeywell programmable model, and wired it up with the wires going to the same terminals. I turned the A/C on, and the blower unit and the compressor outside kicked on. It ran for a few minutes, then stopped, but the icon on the 'stat showed that the AC was still running. I checked, and the compressor outside was still running, the blower motor had stopped though.
I turned it back off, waited, turned it back on, same thing; blower not coming on. I turned it back off, and turned the fan from Auto to On, and the blower didn't kick on then, either. I tried re-seating the wires in the terminals to make sure they had good contact, but nothing changed. I'm pretty sure this is a good thermostat, I used it in my apartment for over a year, and took it with me to the house (not to mention that it worked for a few minutes before the blower motor shut off and wouldn't come back on).
I've re-installed the old Sears 'stat, and everything works correctly again. Anyone have any ideas of things I can check/try before purchasing a new thermostat?