a/c problem

I have a 1998 379 pete 3406e cat. My a/c won't turn on. I checked the fuses. and the relays and everything is ok. The relay that says a/c I pulled out. I get power out of two terminals from the relay. I replaced the a/c low and high pressure switches. On the low side pressure switch I get power from one side. On the High side I get power from both sides. I have freon in the system. I jumped the a/c compressor and it goes on. The switch that turns the a/c on in the cab, i get power out of two terminals. when it's off I get power out of one. When it's on I get power of of two. I appreciate any help. Thanks

 

With the key on and the truck not running should you have 12 volts from the wire on the compressor?? Or does the truck have to be running.

 

I did further testing and this is what I found out.

Low pressure sensor - power on both sides

Jumped the low pressure sensor - compressor did not go on

High pressure sensor - power on both sides

Engine fan pressure sensor by radiator - power on both sides

Fuse box with a/c relay out - power on 86 and 30
ground on 87
nothing on 85

Fuse box with a/c relay in - power on 86 30 and 85
ground on 87

Took cover off a/c relay and put it back in fuse box - I pressed the contacts and the compressor went ON
when I release the contacts the compressor goes OFF

A/C on/off switch - when I turn the a/c switch OFF I get power to one terminal
when I turn the switch ON I get power from another terminal

Any help will be appreciated thanks.

 

Thanks I really appreciate the help. I tried grounding the 86 and all it does is spark. I have the wire diagram and it is showing power going to the 86 and 30. I really don't understand where the ground is at, it really doesn't show it. The wiring schemadic I have is SK25756.