1991 XJ AC issue

I put a used, replacement compressor in my XJ. Mechanic evacuated the lines, charged it up, etc. Everything worked as it should, then the compressor stopped. And then it started working correctly again the next morning. And then stopped again. If I “jump” the relay connections, it runs fine, air is cool, etc. what’s throwing me off a bit is that the ac control on the dash still switches the compressor off and on even when the relay is bypassed. Is this right? I thought bypassing the relay was a “constant on” as long as the ignition was on.