a/c question

[kittom]

having a problem with my a/c. 1999 gmc Yukon with rear air. its never been nearly as cold as it should be but it did cool somewhat. Now sometimes when you start it up it gets somewhat cool but if you stop and turn it back on its no longer cold? any ideas. I was thinking of replacing the compressor,condenser,dryer and cap tubes? what do you think?

thanks, tom