Do I need to level the outdoor AC cooling unit?
It should be as level as possible. The previous posts make good mention of rubber mat 6x6" squares and careful approach to only tip the unit as little as possible not to kink any lines. If you don't hire a professional and aren't confident by yourself to address the issue, having a second person watch the lines while you tip can save much potential trouble. Previous information from these posts also generate ambiguity over the importance of having the unit level in regards to the compressor. Leveling the unit will terminate any ambiguity. An additional concern not previously adressed is the compressor and/or fan bearings. An off level unit will put additional unintended mechanical stress/strain on these rotating components long-term. Therefore for best performance and longevity of your unit, level it and take special precautions in the process.