Road junk killed my air conditioner condenser...

It can be difficult. Of course, anything with obvious damage is out. Look inside the connectors for corrosion. If the A/C system was left open in the junk yard for very long, it is suspect. Try and blow air through it. I don't know if anybody does a pressure test. But with a bicycle tube you can test it up to 15psi for leaks. Operating pressure are considerably higher than that, but it's a start.

Thanks; I'll be sure and check that out first.

voice from the past

Some parts should just be replaced with new parts. This is one of them. I wouldn't trust one from a junk yard. If you got a bad one, the savings would quickly be eaten up with the time & expense of redoing the job.