A sight glass is placed on the line that comes from the outside condensing unit. 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.
When looking at a sight glass it is important to look for bubbles as they may be an indicator of an issue like low freon levels.If the outdoor coil is dirty or the outdoor fan is not moving enough air, you will also see gas in the sight glass. It is important to contact a licensed HVAC contractor to diagnose your system if you think that it is low on refrigerant. The EPA has guidelines for servicing and maintaining HVAC equipment and it is important to follow those guidelines. If you are in need of a technician we are available 24/7: 239-596-5855.