I've read somewhere that the outdoor AC unit needs to be leveled. My outdoor unit is a bit slanted due to the floor not being completely flat (pic below). However, I don't see any obvious structural issues. Is this something I need to correct? Perhaps by sticking a small piece of wood on one side?

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    Not an AC guy, but when I had one installed at my house, my AC guy was very careful to level the slab. Shims should fix it; you might even go for plastic ones for rot avoidance. Jul 15, 2015 at 1:52
  • Thanks. Plastic is a good idea. By the way, did your AC guy explain to you why it had to be leveled?
    – Zoomzoom
    Jul 15, 2015 at 1:55
  • He probably did, but I'm afraid I've since forgotten... maybe someone will pipe up with a worthy answer. Jul 15, 2015 at 2:28
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    The compressor shock mounts would really appreciate having an even loading by having the compressor sit as near plumb as possible. That thing thrashes about a bit on motor start and stop. As would the oil sump at the bottom of the compressor. Jul 15, 2015 at 4:53
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    The wood or plastic would be fine, the bottom of the outdoor unit is a pressed metal frame that the shock mounts attach to. Leveling the base is all that's necessary. If you're worried about contact area, just use a wider wedge. The shock mounts isolate the hermetically sealed compressor unit from the base for noise reduction and absorbing the startup kick. Jul 18, 2015 at 16:57

6 Answers 6


Refrigerant needs to flow through the coils evenly without too much interference from the slope of the unit. A level concrete slab with rubber pads between the unit and the concrete is what the manufacturers recommend. "Mostly level" is probably okay for a residential unit. Get a half-inch thick outdoor rubber mat and cut it into 6"x6" squares. Put single pieces on the high side and stack several pieces under the low side to bring the unit closer to level. Be careful not to kink or damage the refrigerant piping to the unit when you do that. If you damage the lines when you raise the unit to insert the pads, you will wish you had left it alone.

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    "Probably okay", is right. OP thinks that's unlevel? If only I had some pictures... "Wish you hadn't touched it", is also correct.
    – Mazura
    Jul 18, 2015 at 19:37
  • Not being level can cause the oil for the compressor to not lubricate correctly. Over time it will cause the compressor to burn out costing you lots of $ in the long run.
    – Brandon
    Jun 5, 2016 at 0:48

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.


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.

Slope Tolerance

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"



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.



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.


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.

  • Well, this unit came with the house when I bougt it, and is 17 years old. So unfortunately I don't have the specs/manuals for it.
    – Zoomzoom
    Mar 28, 2017 at 20:38

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