Homeowner with a 1991 split system heat-pump now. A/C Contractor friend says it's time to upgrade to a 13-seer R22 unit. Says that I should not wait until later because of the R22 phaseout. Says R-410a not good choice in the desert because R-410a loses significant efficiency (like 40%) at 130-140 degrees, which is likely in a desert attic in the summer. Says he has clients who's R-410a units run continuously in the summer, doesn't cool their house, pay higher electric bills. Also says the new units come with two-speed motors and that they are very expensive to replace. Says warranties also not as good on the R-410a units. The proposed R22 system has a 10-year warranty. Obvious drawback to the R22 system is that R22 freon will get harder to get and will be pricier over time. Any advice or thoughts?