Thank God most window units are "sealed" system. Keeps most people from screwing with them, and screwing them up!!
Some idiots insist on installing mechanical "tap valves" which INVARIABLY leak, even if the unit did not do so before! If you must "tap" one (avoid if possible) get someone smart enough to silver solder access valves to the process stubs!!!!
What DrFridge said is most important!!!! Good water flush of condenser (outdoor coil) is a necessity as well. They get ignored and bake on an unbelievable array of crud. Result is poor cooling, high operating costs and ultimately destruction of the unit. Give it a bath!!!
Dave, I can see how we came to disagree. Cars, window units, residential central units and refrigeration are all very different branches of the HVAC/R trade. The theory is the same but the technology and it's application are far different. Had a few beers here and just felt the need to clear up some misinformation. And yes, I do this for a living!