The ac has been inop quite some time in this truck, and I didn't really miss it much in the upper half of New Mexico, however I am cruising to Chicago in a couple of weeks...so I began troubleshooting, and have determined the leak is in the evap cooler. While charging the system, frosty smoke exits from the firewall at the connector block, so it may simply be a cracked solder joint on the tubing from the firewall block to the evaporator core. I do have the GM factory shop manual, and their process calls for completely stripping out the dash, more or less, to get to the AC module removal...:-( With an important trip looming on the horizon, I am somewhat reluctant to begin this chore. This appears to be a solid 8-hr job, with a lot of possibilities of creating intermittent harness connections, and other areas where Murphy would love to play!! Any words of encouragement or caution from anyone who's been there -- done this? Thanks! Tom in NM 2003 2500HD Duramax mountain goat.