No heat all of a sudden

I have a 2001 Sebring convertible and she suddenly stopped putting out warm air. I don't think it is a thermostat or heater core problem, because the temperature guage still goes to the same reading it always has, and takes the same time to get there. I had more heat than I could use one one day, and the next there was no heat at all, so I don't think its the heater core, either. she will switch from floor to vent to defrost ok, and the blower motor works. Any suggestions on where to start checking?

Most common issue of "no heat" is low coolant level. How is yours? You may have a leak if low.....

Coolant level is topped up.