1996 GMC Jimmy engine warms up

SO MY AC BLOWS ICE COLD ON THE HIGHWAY BUT WHEN I COME TO A TRAFFIC LIGHT THE TEMP GAUGE GOES TO HALF WAY OR A LITTLE HOTTER THE AC CUTS OUT THEN THE ENGINE ROARS LOUD AS IF A FAN IS KICKING ON AND COOLING IT OFF WHICH IT WILL COOL DOWN BUT ONLY WHEN I START DRIVING IF I DONT RUN THE AC IT RUNS PRETTY NORMAL IN BETWEEN COLD AND THE HALF MARK THAT ROARING NOISE ALSO HAPPENS IN THE MORNING THEN QUITS AND ENGINE SOUNDS NORMAL IT SEEMS LIKE A FAN CLUTCH OR A RELAY PERHAPS! WE JUST REPLACED THE AC COMPRESSOR AND CONDENSOR BUT IT STILL HAD THS PROBLEM BEFORE AND AFTER. PLEASE HELP ITS TOO HOT TO BE HAVING THSE PROBLEMS OR SHALL I JUST TRADE IT IN HAHA