Weak cooling can have more than one cause. Share whether airflow, temperature or unusual noises have changed; inspection should come before any refrigerant decision.
Tell us if the AC cools only while driving, if the fan speed has changed, or if cooling has faded gradually. These details help distinguish a control, airflow or refrigerant concern.
What can be completed at the vehicle depends on the condition and job. Any different arrangement should be discussed before work is agreed.