a/c compressor burned out?

My a/c quit working, no cool air. About a year ago a repairman did something
with a switch in the attic that he said would normally be replaced at a cost
of $150 or so but that it really wasn't necessary. He has a good rep and no
reason to have me spend less.

Nos the A/C quit working. I called another company as I couldn't locate the
other guy. The tech came out, took a look at the unit and said the
compressor was probably frozen but that he couldn't tell until he put a
booser on it to see if he could get it running. He said it was turning off
because it was overheating and was getting a signal to turn on. He didn't
look in the attic or mention anything about a disabled switch.

It's a carrier. I don't have the BTUs.

Any suggestions? What should it cost to replace the compressor it that's
what turns out to be bad? The A/C is 10 years old. Should I replace the
whole unit, if the compressor is bad?

: -)