How do I diagnose/fix my AC...Is a system flush required? Door blend actuator? on 2002 Ford Explorer

My AC won't stay charged after jump starting the AC fan clutch with the relay switch. 2 cans of refrigerant later, it only stayed cool for 5 days. The rear vents blow HOT air when the AC is on, suggesting that I need to replace the rear door blend actuator...this however, is not the problem under the hood :(

Asked by for the 2002 Ford Explorer
Find and repair the leak, if you had to add Freon, then it is leaking somewhere.