Professionally converted to R134a approx 5 years ago: Pressure good, freon good, no leaks. MB shop was going to replace compressor but when I drove it in next morning it was working.

Here's how it goes, car cold: crank A/C works fine. Don't turn car off drive forever A/C works fine. Turn off car at any point to go in store whatever, compressor will not turn back on. Any suggestions? Thanks in advance.............Nate