There is no maximum that an air conditioner can have of refrigerant.
The charge would have to do with the length of line set.
The minimum charge is listed on the condenser.
It is illegal to keep charging a system that is leaking.
That technician needs to find the leak.
The technician can use a few different ways to find the leak.
As a last resort, the coil can be removed and pressure tested.
The technician can also use an electric refrigerant leak detector as well.
It is not okay that the system has been charged multiple times without finding the leak.
It is against the rules that anyone with a refrigeration license must follow.
Depending on the efficiency of your condenser you can just replace the evaporator coil.