My 2000 has approx 32k miles and is now on the 3rd compressor. A/C temp kept going up and when I took it in they said bad comp on the first 2. I have had A/C systems replaced out of warranty and they always said they wouldn't warrant it unless comp, evap etc were all replaced. So why just the comp when it's under warranty?

 

Third compressor? There is obviously some condition with the system that's causing the failures. Sounds like the dealer doesn't know what's causing them to fail.

 

When they change compressor are they also changing the piston? Sometimes called a strainer. This is what regulates amount of refrigerant going through the line. It is simply a measuring device instead of a expansion valve that use to be used. Many times when the compressor goes out it scrambles the inside of the comp. , small metal shavings go through the system.
They will all collect in the piston (strainer) and the accumulator. The system must be clean or you will loose another comp. Installer can also install a filter which will catch the metal but it too can become stopped up. The best thing to do is replace the accumulator, piston (strainer), and add a filter drier. Recharge system, monitor pressures with manifold gauges, to make sure there is no more restrictions, after system runs for a while remove filter drier , it catches metal particles, and either replace with another filter drier or run system without filter drier.
I have seen a hand full or metal shavings come out of a a/c system. Hope this helps.