Serpentine belt woes

[lhul5ley]

I have a 1993 GMC Sierra 1500 pickup. We've rebuilt the motor (less than 20k on it) have a relatively new alternator, replaced every pulley there is to replace, and there is a new compressor for the A/C that is about 2 weeks old. We've ran the truck about a week and we are still getting the same problem that we've had for quite a while with the belt. It keeps riding up/ back on the pulley for the compressor and is cutting the plug to the compressor. The best mechanic down at the dealership here believed it was a spacer that was missing on the bottom of the compressor mount (Part 16 on my diagram). My dad said the spacer was removed by the last mechanic that attempted to line the belt up properly, hoping this spacer not being present would result in the compressor tilting slightly forward and preventing the belt from walking back. Would the GMC mechanic's theory not be inaccurate? If the spacer is at the bottom it seems as if it would only make the alignment worse for the problem we are having and result in the belt walking back easier. Any solutions or ideas would be welcome. Thanks in advance

[Jsdirt]

That makes no sense to me - tilting the compressor forward is obviously going to make the belt go backward (towards rear of vehicle).

 

The mechanic must've lost it & figured he'd make up a story ... ?? Who knows.

 

The spacer was there for a reason. Put it back.