Just installed a AC compressor and dryer on my Cummins, went to add freon to it ,but didn't hear the clutch come on and could not add freon, any help

 

When the system is empty, the compressor won't run. Need to feed refrigerant to the low pressure side, and once there is enough in there, the compressor will start cycling, and will draw in more.

What are you driving?

 

What vehicle please so this can be moved to the appropriate tech section.