Got a service call on a Carrier condenser that wasn't working. Found the suction meltaway relief valve open, and the entire charge gone.

Condenser fans seem to be working, and everything else control wise seems to be working. Not sure how this let go, and never seen a suction one let loose before. No one was soldering near this thing or anything like that.

Wondering if any of you guys have seen the same, and what the apparent cause may be.

It's about a 20-ton condenser with a recrip compressor.