My central AC compressor unit is outdoor resting on a concrete pad. The pad
is 48"x48" in size and 4" thick and it is reinforced with steel rod. I
believe the pad is original so that will put it back to 1980 when the house
was built.

Recently the concrete pad started to fail. First a crack started about 8
inches from one edge, then more cracks along the outside edges, chunks of
concrete started to fall off exposing the rusted steel rods inside. The
compressor has four legs and it's bolted to the pad with concrete screws.
Of course with the pad failing two of the compressor legs will no longer be
resting on anything solid real soon.

Obviously I need to remedy this situation. But I have two questions:

(1) Is it normal for a pad to fail like this after 20 years? Why did it not
fail after 8 years or 12 years? If it waited 20 years, does it mean there
is some other factor involved? Like perhaps the soil below is yielding due
to a sink hole (house is in coastal south Florida sandy soil high water
table) or sewer line leak?

(2) If I replace the pad how would I go about doing it? I cannot just lift
and move the compressor aside which is very heavy and has very rigid
connections into the house's attic. A new pad will take a day have the form
done and the concrete poured, then a few more days at least to cure. I will
have to wait a while to put the compressor on again...do I get a concrete
repair place to fix this or the AC place to fix this?

Thanks,

MC