We bought our house this past summer, it was built in 2003 - typical builders grade AC (actually undersized for our house so it works overtime), 80% efficient propane furnace. We have a new EPA wood stove which we use to reduce our propane use in the winter significantly. So...our AC is on it's last legs, but both systems are 14 years old. Our options are:
1. Just replace the AC unit with as efficient of a unit that our furnace can accommodate (no 2-stage or variable stage units will work with our furnace - which happen to be the most energy efficient) Cost ~6300
2. Replace both the propane heater and the AC unit, upgrading both to more efficient 2-stage systems and we'll be set for the next 15 or so years Cost ~11-13k depending on the exact units we choose (also includes putting 2 heat vent drops in our unheated basement)
I'll kick myself if we just replace the AC and the furnace goes shortly thereafter, but monetarily it's a bill pill to swallow.