2001 peterbilt 379 Detroit 12.7 60 series fan won't stop running.

The AC system is all brand new and the AC clutch is not engaging when I hit the switch in the cab. Could that be the high pressure switch which is also causing my fan to run?

 

Yea I've had a couple people telling me to just say screw it and throw a fan clutch in it but parts are never cheap I'd like to narrow it down and not just throw thousands of dollars at it with parts that were still good. I checked all wires coming from ECM also knowing that those can be a problem. I checked all grounds on frame and firewall thinking it's a electronic issue and I still think it is.

 

I'm not sure it was done before I bought it a couple years ago at a shop. I guess maybe I need to go get a gauge and see if it's way to high. I run local in North Idaho therefore the AC doesn't get a whole lot of use.

 

No access right now but maybe that is the best route when I get home.

 

No it just started running all the time. Before it was working perfect! I parked this truck for a few months as a backup and I noticed it when I went out to start for awhile the other day.

 

Also the fan doesn't spin by hand when the truck is not running....I know on my cat it does.