Do you have a sigh glass on the liquid line of your air conditioning system at the condensing unit? It should look the photo in this video post. It is a small glass window in the small copper line near the outside portion of your air conditioning unit. This is a little window on the performance of your air conditioning unit refrigerant.
Look at the glass when the unit has been running for a while. The glass should be clear. If there are bubbles in it then your system is likely low on refrigeration or you have some other problem. In this video you can see the green center. There is a color chart shown around the perimeter of the glass to indicate what changes in color mean. This color dot is intended to indicate if you have excessive moisture in the refrigerant which can get into the system during charging. In this case green is good. If it shows that the refrigerant is wet then the system may not cool well and you may need a new filter dryer.
If the glass is clean and clear it does NOT mean you are also in the clear. It just means the system is not low enough to show up in the glass. You should still have yearly evaluations of the system normally in the spring for cooling and in the fall for heating. The glass will not show a system which performing near proper performance and thus you may be losing energy. A checkup should be done by a licensed HVAC contractor. This will insure the system is running safely and efficiently.