What he said, The belt contact area on the alt pulley, is marginal with AC, which makes having good belts with proper tension a must with the big alt.
Originally Posted by JeepWrencher
Not to speak for MDill as I'm sure he can do that but I think he is talking about how the belts don't wrap very far around the alternator pully if you have AC.
With AC you have to wrap from the Crank, Alt, AC, Water Pump. This means the actual ammount of Alt pully that is in contact with the belt is pretty small due to it having to go up the block and drive the AC instead of wrapping around the pully and going straight back to the WP. Even when the AC isn't being driven just the fact that it is there means there is less contact patch for the belt to drive the Alt.
If you removed the AC as you say then you have a better situation for your belts to live in. Personally since I still have my AC and have to tension my Alt from the bottom and can't get a good angle on it, I have to tighten it as much as I can, then make it a little tighter, then pull a muscle getting it a little tighter before I snug it down.