You shouldn't need to recharge the A/C unit at all unless there is damage to the unit that allowed freon to leak out.
There is some care that needs to be done to A/C units.
- cleaning the filters on the return air system.
- get up on the roof and look at the back of the a/c unit. The fins need to be kept undamaged. Some times tree branches will rub against them and bend them. If you are very careful you can straighten them out.
Also, if you have a heat strip, make sure you don't have the setting on for heat. This will sometimes cause you to think something is wrong, when there's not.
Give the air a head start on the heat of the day. To offset heat gain:
- Close windows and blinds.
- Limit use of entrance doors.
- Use awnings.
- Avoid heat-producing appliances.
Make sure outside power supply is not below 108 volts.