a/c question

[99yukon350]

i have a 1999 yukon with rear a/c and i have recharged it twice. it had die put in it before i bought it and i have gone over everything with the black light and yellow glasses. i could not find any leaks except for a valve core at the ports on top of the compressor and i replaced that and recharged it. it worked for a little while but now there is no freon in it and it wont turn on. do you know if there are any common places that leak that i might have missed.

 

[roadrageror]

there are lines that run along the frame near the back tires on the pass side that are prone to getting hit by rocks and getting cracked..this could be the problem.i dont know if you can just plug the lines for the rear..and there like $600!! or close to it.