96 Lumina LS AC problems

I have a 96 lumina ls with 75000 miles on it. I replaced the intake and head gaskets last fall. Ever since I did that The ac quit working. The only thing I did was unbolt the ac compresser from the block for access to the engine mount. There is no power getting to the compressor switch on the side. I do know that. If I ground the switch in the underhood fuse block the compress will run but not cool. If I jump the terminals on the low pressure swith the compresser will not run but I can get both fans to run. I dont see how I could have lost the freon because I did not unhook anything. The ac worked great before the intake and head gasket repair was done. Please help !