Do I need to level the outdoor AC cooling unit?

Outside A/C compressors are typically supported on a concrete pad, concrete blocks, or a vinyl pad such as the one shown in the photo at page top. The air conditioner compressor support pad should be level and secure against movement.

Compressors which are badly out of level may fail to function properly and need adjustment. Tipping and moving compressors can also cause can cause leaks in refrigerant lines, leading to costly air conditioning service calls to evacuate and recharge the system after repairing the refrigerant leak.

Do not try to move your A/C compressor yourself as you might cause a refrigerant leak or may otherwise damage the equipment.

For slightly-tipped air conditioning compressors we generally leave them alone but we add support as needed to avoid further movement.

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For a professional appearance it should not appear to be set without a thought to anything but function as if a war time situation where getting online asap is the priority. The thought that an AC unit must be absolutely level or its wont work or work well is based on absorption type systems RV's used in the old days that used ammonia and a flame rather than a compressor. Technically speaking, no it matters not if its level or even close to it, it can be at a slant but will look weird.

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.

Check the installation specs for your unit to see if it is supposed to be level (most likely) or slightly pitched. There are some ACs (large Rheem units for example) that are supposed to be installed with a slight pitch towards the condensate drain. If you aren't having any trouble then leave it alone. If you are having trouble, then call a pro sooner than later. Routine maintenance on an AC is much cheaper than having to replace one.

Take a look at the installation guide for this Lennox condenser unit. It actually specifically points out that the slab should either be leveled or maintain a slope of 2 degrees.

Page 8 mentions, "PLACING UNIT ON SLAB When installing unit at grade level, the top of the slab should be high enough above grade so that water from higher ground will not collect around the unit. The slab should have a slope tolerance as described in figure 5, detail B"

https://resources.lennox.com/FileUploads/31c2ac16-919c-41a1-ad0c-515f8351eccbLennox_14ACX_IOM.pdf