OK so chances are you broke an Idler pulley.. if your bus has only one serpentine for dual alternators and A/C, it likely has an aftermarket A/C system and a special belt...
there are 3 idlers.. my belt is below which is different as I only have 1 alternator and my AirCon is a separate belt...
on my diagram below.. off to the right is the air Compressor.. and my single alter is just off the left..
the most common idler to break is the one near the right just above the white filter..
all of your pulleys should spin freely without any wobble or heaby resistance. the air brake compressor (if you have one) will be somewhat hard to turn but you should be able to turn it by hand.. .. the belt tensioner is on a big spring and you use a 1/2 breaker bar to lift it.. there should be spring tension on it.. if it just flops around or its pulley is loose then the spring broke in the tensioner..
the outer rings on the A/C compressors should spin freely.. the engine pulley you cant turn by hand