Problem with an extended warranty is that (if it is like the ones I have serviced) it has a clause that says "repairs not covered if due to improper installation". I had one the other day that was a heat pump with an extended warranty that the original installer was no longer affiliated with. The power wire from the disconnect was to long and rub against the inside of the condenser. After several years of operation the insulation on the wire wore out causing a short that burnt the wire completely in two. Customer had to pay for the repair.