We've lived in our house 11 years. Our air conditioning (condenser) unit, the big boxy thing sitting outside, is not sitting on a concrete slab. It's just sitting on the ground and we noticed this spring that water was pooling and it was actually sitting in several inches of water. Them more I think about it, the angrier I get that the inspector didn't catch this 11 years ago. I've read that mounting it on the house is the best solution but that's not an option. What do I need to do (get a concrete slab poured for it to sit on and check yearly that it's level?) and who do I call to help (an electrician?) I obviously don't know what I'm doing so any help is appreciated.

  • 1
    Have you looked up the manufacturer's installation instructions?
    – Jasper
    Sep 24, 2015 at 3:36
  • 2
    They make pads out of plastic and concrete, that are designed for condensing units to sit on. You might be able to lift the unit just enough, so you could slip one under it. It might not lift it out of the puddle, but it might allow you to keep it level.
    – Tester101
    Sep 24, 2015 at 4:00

1 Answer 1


Code requires outdoor condensers be installed on a reasonably level surface raised at least 3 inches above ground level. If water pools in the lower part of the unit during cold weather and then freezes, the condenser coils can be damaged by ice expansion and that will often end the life of the unit, although the outdoor condenser can sometimes be replaced.

As Tester101 said, there are prefab pads made for this and if you can raise your unit without damaging any lines that are connected then you may be able to do this without an A/C technician. Great care must be taken not to kink or break the refrigerant lines if you attempt this. Otherwise, you will need an A/C contractor to recover the old refrigerant and disconnect and temporarily cap the lines; and then after you install an acceptable pad the A/C contractor will need to install a new refrigerant dryer, reconnect the lines, purge the lines with nitrogen, evacuate the system to a deep vacuum, and correctly recharge the system with new refrigerant. If everything goes well this is around a half-day of work (not including installation of a new pad).

By Request:

2009 Uniform Mechanical Code 1106.2 "Supports and Anchorage" last paragraph:

A compressor or portion of a condensing unit supported from the ground shall rest on a concrete or other approved base extending not less than three (3) inches (76mm) above the adjoining ground level.

Admittedly, this language does not use the phrase "reasonably level" and it is not the most current version.

  • Also, certain states, have "hurricane" provisions requiring 'concrete' slabs.
    – Ruut
    Oct 7, 2015 at 16:38

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