How cool is the air coming out of the dash vents? Test conditions:
About 20 degrees ambient and no sun
Engine warm and idling
Doors and windows closed
CCU settings: Min temp, max fan, Resirc on, upper slider to leftmost position. (or big snowflake button pressed)
Measure at dashboard centre vents, you should read 7-9 degrees C.
Is the A/C compressor cycling on and off at engine idle? If so, pressure is OK in the cooling system, and you do not have a leak.
As mentioned above, the most common failing part in the A/C cooling system is the evaporator. This is easily checked by a A/C technician using a electronic sniffer. They can poke the instrument through the resirculation flap under the dashboard, right onto the evap radiator.
The most common fault in the ventilation system is failing servo motors. One or both of the mixer servos may have given up the ghost, and may have stopped in the open position. Heated air from the engine will then overshadow any A/C cooled air.
Servo testing is easy, see my DIY pages.
Cheers,
Tore