If it's not the rear A/C lines, then it's probably that little Schrader valve on the low pressure port where you add the refrigerant. Best to do the job right with replacing the little valve, then drawing a vacuum for 45 minutes and adding the correct amount of refrigerant, by weight. Otherwise you're asking for trouble with the low-slung compressor on these rigs.Also when I went to lunch today I am seeing my AC compressor won't kick on and the light is blinking.
Those little cans you get at Autozone with the gauge are $hit. Troubleshooting A/C stuff is one of the things I'm willing to go to a pro for.