Hello,

I have an '84 since new with AC.  The AC has about as much impact as you'd 
expect it to, but the bus still goes 70 with it on.

The loss in leaving the belt on is tiny.  However, if you never ever plan 
to use the AC, why take chance in having the compressor clutch bearings 
seize and cause all sorts of other irritating problems?  And, the next 
owner may want to use the AC and those bearings will be like new for him if 
you leave the belt off.

I use the AC about 4 months a year here in Phoenix, and of course, the belt 
stays on year around.

Mike