1998 Chevy Lumina AC COMPRESSOR CLUTCH WONT ENGAGE

Air Conditioning problem
1998 Chevy Lumina 4 cyl Two Wheel Drive Automatic

Freon level is correct, all fusue are OK. When I ground post 4 on the AC clutch relay the ac clutch engeges. I'm thinking that the problem is a bad low pressure cycling switch, but I cant locate the switch so I can bypass it to see if the ac compressor engages. Do you agree or do you know of another problem I've missed. If so can you tell me the location of this switch on a 1998 lumina with a 3.1 a/t? Thank you