You could have a bad blend door actuator but I'd bring it to a shop who can hook up an AC machine and read pressures. You may also have a leak and moisture in the system.Use this link to find a good shop near you.https://repairpal.com/repair-shops
Alex
RepairPal Certified shops can diagnose and repair your 2001 Toyota Avalon. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.