Fan always on with A/C

Hello forum brothers... I am looking to troubleshoot an a/c issue i have. The truck is an 2001 379 with a C12 and when i turn the a/c on the fan comes on and stays on.

This is obviously robbing me of both fuel and power and need to get it fixed. Aside from taking it to the dealer i wanted to see if it was anything that I could do myself and save the labor cost.

What could the cause of this be? i appreciate your help and hopefully can get this taken care of soon.

thanks

 

Your trinary-binary switch goofing up or did someone wire it into fan switch?

 

Is your condensor clean? If its plugged up the fan will run to try and bring the high side A/C pressure down.