Serpentine belt

I have a 95 Riviera, a few weeks ago my idler pulley froze and broke the belt, and broke another pulley. Had a shop install new pulleys, drove it for about 20 miles and the belt slipped off. The shop towed it and couldnt figure out why it came off, the chalked it off to maybe missing a chunk of the old belt.
Drove the car for about 10 miles and the belt came off again, seems to happen as Im getting onto the highway.
Shop towed again, and found my cooling system not working, replaced the computer, fans now work fine.
Drove for about 10 miles again and the belt came off, shop said supercharger was making noise, which i agree it was, 150,000 miles ;), had the supercharger rebuilt.
Drove AGAIN for about 10 miles and the belt slipped off again! Shop says they suspect the A/C compressor, but I have never heard of this causing a belt to come off, unless of course it is making a ton of noise because the bearings are completely shot.

Please does anyone have any ideas? I really like this car and would like to get it running again.

Thanks

what belt are they using? the 95's had different belts than the 96+ rivs. there should only be 1 belt on the 95' where the 96+ had 2. you should get a second oppinion from another mechanic shop that you trust. 150k miles isnt bad for a 95 riv. the engines last a long time and the supercharger last even longer. good luck
Matthew

Just got back from the shop, believe it or not, the A/C is causing it to walk off the water pump pulley :uhoh: . Runs fine as long as I dont ujse my A/C or defrosters. Thanks for the reply. btw my 95 has 2 belts. One for the Alt and power steering, and another for the SC, AC, and waterpump.