Where is the low side of the air conditioner on a Chevy half ton pickup truck?

Depends. What Year ? On Most Of 1996 And Later It Is On Top Of The Compressor. These Use R134A. If Your Isn`t That Design And Uses R12 Follow The Large Line This Is The Low Side. You Should Locate It That Way. Best To Let A Good Garrage Service Your A/C You Most Likely Will Be Better Off. GOOD LUCK