I replaced the a\c compressor on a couple trucks, after I pulled a vaccum on it I recharged it to almost the right amount. Got up 80 psi in the low side. But the compressor would not kick on. Do I need to reset the computer or something?

 

no.

make, model, engine year is...

turn on the system and briefly, jumper the low pressure switch. if the compressor runs...you have a pressure problem or switch circuit problem.

if the compressor does not run...check the compressor fuse, relay.

 

I don't see how it would be the pressure switch. They both worked fine until they broke. The one ( 2004 Mack semi) the bearing locked up the other ( 2006 f250) the clutch material itself broke. I read a couple places that you had to unhook the battery to clear the low pressure code, but that didn't work

 

your at the wrong site then as this is a gm forum. I cannot speak to the specifics of a mack truck.

I was trying to give you a suggestion based on the limited information you provided.

gm vehicles, and every other brand of car and light duty truck i have filled; as soon as the system is filled enough to close the low pressure switch, the system works.