The refrigerant (freon) in any air conditioner should last the life of the unit. If not, you have a leak.
10 years
It would take 30 min. average time to add this charge to the system.
after twelve thousand years, so don't worry
If the system does not have any leaks, it will last forever.
The shelf life of clean, dry refrigerant is indefinite. As long the the system is free of contaminants, the freon will be good.
It sometimes depends on the temperature difference between the condensing unit and the air handler. I would say normally no more than an hour.
Possible freon leak in the coil of the unit and the fan is circulating it into the air. As we know freon is toxic to the environment imagine what it can do to a human body.
When well-maintained it can last for ten years.
You can add a tapping valve(which almost always leak after a long time) or braze in a schrader valve.
Until a leak develops which allows the refrigerant to escape.
Yes, a central air conditioner can be installed in a house that currently uses room air conditioners as long as there is a place to put the fan outdoors.
"Overcharged" with freon,, just like a credit card, ..overcharge and it stops working.