Inspect Evaporator And Fittings For Leakage Of Refrigerant
WARNING: This page is about a different car, the 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
Using a gas leak detector, check for leakage of refrigerant.
If there is leakage, check the tightening torque at the joints or check the evaporator.