A must or just a good idea?

[gtblum]

Do ac units have to be installed on pads? It's been there for eight yrs.

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[davidlord]

Around here they do. M1403.2 Foundations and supports.

Supports and foundations for the outdoor unit of a heat pump shall be raised at least 3 inches (76 mm) above the ground to permit free drainage of defrost water, and shall conform to the manufacturer’s installation instructions.

[msteger]

I always see compressors either sitting on a pad or wooden platform. I don't recall ever seeing one without one, although I have seen ones that aren't level and need attention.