So i have this 2003 Tahoe, Ive been a mechanic my self since i was a kid i grew up in a shop building small block chevys and watching my dad work on cars, i spent 10 years as one my self after high school and got bord and went in to Air conditioning and refrigeration. Last summer i put a new compressor, dryer accumulator and orfice tube, all new parts. Holds 3 lbs with rear a/c. System runs at 45-50 low side and 200-225 high side. but if it sits at a light and idles, the thing will start making the tensioner smack its stop extending its self as far as it can go. like a rattler its so fast, and its a horrid noise to. i have to keep it under 1500rpm to keep it from flying apart. or turn system off before I get moving, i thought clutch fan was bad so i replaced it. no luck same crap.  Its like liquid is making its way back to compressor and is locking it up momentarily ive snapped belts. Ive put like 3 belt tensioners on it now. Broke one clean off. Ive also under charged it. Just to see results. so ive been driving arond with a half ass working a/c system and it still break shit up. Im going to take it all out again an weigh in the 3 lb one more time to make sure there wasnt some mistake ive over looked but have you ever had this sorta thing happen to you. I always get the crasy stuff. Is there a over pressure switch i dont know about, i thought there were only low pressure switches. im stuck man