Alex wrote:
Hello everyone,

Monday night our AC unit (electric central air and heat) started
making a strange squeeling sound (like a loose belt on a car) then
acted like it was loosing power... going normal then slowing down
then normal again, etc. I turned it off and called a local repair
shop which I've used in the past.

They came out today, and after turning the break back on, the repair
guy touched the outside of the unit to get a shock which threw him
back a few feet -- he touched the outside of the unit, nothing
internal. After turning the power back off he did more digging and
said the compressor was grounding and either the compressor needed to
be replaced or the entire outside unit needed replacing.

Huh?

There are two moving parts - that could cause a screeching noise - in the
outside unit: the compressor and the fan.

My bet is on the fan (a $300 item).

I'd have someone else have a look. It's customary, when a repairman doesn't
know what's wrong, to replace the whole thing.

You may just have a burnt wire...