If light is not coming on, then first thing you should check is fuses related to air conditioning system. Check these fuses in 2nd generation Toyota Avalon (XX20; 2000-2004):
29. ECU−B (7.5 A): Air conditioning system, theft deterrent system, power seats, meters, power windows (for driver and front passenger), multiplex communication system.
34. HTR (10 A): Air conditioning system
37. A/C (10 A): Air conditioning system
39. PANEL (5 A): Gauges and meters, audio system, cigarette lighter, air conditioning system, emergency flasher...
59. HTR (50 A): Air conditioning system
