How do you charge ac?

If the system is empty you probably have a leak so charging it back up will be like throwing money out the window plus you are discharging freon into the atmosphere. Take it to a qualified garage for testing and repair.
If the system is empty you probably have a leak so charging it back up will be like throwing money out the window plus you are discharging freon into the atmosphere. Take it to a qualified garage for testing and repair.