I am not a professional. Just documenting how i repaired my friends condensing unit.
This AC stop working and blows hot air. The condensing unit fan was running but the condenser didnt run because the run capacitor was bad. The run capacitor stores up charge to kick start the compressor and fan.

Many asked where to buy a run start capacitor? Search "HVAC supply" in google maps and a local AC supply store sells it. Or go to online stores like Amazon. The following link goes to Amazon's capacitor section:
http://goo.gl/4Xgwb