This is the 2nd summer that my 04 Forester (145,000 mi.) has had this AC problem, and the third mechanic look-see, this time at the dealership. Works fine most of the year (use it to dehumidify), until it gets hot - 83 degrees or so. Then it cuts out. The fan still works, but no cool air. Sometimes stopping the car (like at a stop sign) and then starting up again will kick it back on. Occasionally will start up again with no apparent ambient changes. Always suddenly off and on. Every time I've taken it in, they've all noted that it's "slightly low on refrigerant," but either reproduce the problem, when it happens, they can't tell where the problem is. Two have recharged the system but couldn't find leaks. (Also said the amount it was down would affect the temp of the cooled air, but not this problem.) The dealership is speculating on an evaporator temp thermistor, but says they can't test it - that it would be a leap of faith, and $650. They said they checked the electrical system. We're driving through South Dakota in this thing in a couple of weeks - it was miserable last year. Help!