Leaks can be found anywhere in a refrigeration system including sight glasses. In this video we have a leak on our semi-hermetic compressor sight glass. The sight glass here in particular shows us the amount of oil (and its condition ) inside our compressor. As you can see when I squirt some big blue on it bubbles start forming. These bubbles mean that a leak is present. Now, in this video I use a long flat head screw driver and a hammer to tighten the sight glass but there is a tool out there in the market that is strictly for tightening sight glasses. The link to purchase that tool is —> https://m.johnstonesupply.com/storefront/product-view.ep?pID=H28-016.