a/c clutch will not engage on its own

I have replaced the thermistor, relay and dual pressure switch. I have changed over to 134 and we added dye and the a/c worked for about a week. Took it back to my biddy's shop and it had lost about half the charge we could find no leaks what so ever even in the cab behind the glove box no leaks. Then after the truck had been running for a bit the clutch stopped. We can manually get the clutch to engage but it will not on its own. Right now the system is empty because I was planning on installing a new compressor at the house but I really don't want to buy another part I don't need. Thanks