There should be a metal tag with the identification number and all details stamped and riveted to the back, sides or even underside. But usually on the back of the unit. But whatever is written on it is meaningless if your unit is not cooling to your satisfaction, plus it may have lost the refrigerant over the years and become less efficient. So depending on the room size you can buy a new unit. Or depending on which county you are in you may be able to have it recharged with the refrigerant.
it depends the temperature,never is the same time,depends how hot or cold is the weather.depends the thermostat regulation by the user.
colder sets get more time running at hot weather