doesnt cool properly
will a dirty air filter affect the ac? on 2000 Toyota Sienna
A restricted "Cabin Air Filter/Pollen Filter" would definitely affect the ventilation inside the passenger compartment if that's what you had been told or heard but the 2000 Sienna does not have provision for a cabin air filter.
No, a dirty air filter will not cause the A/C system to operate inefficently. Pressure readings will have to be performed to determine if the root cause of the A/C system issue. I suspect it may be low on refrigerant from a small leak.