Am I correct that the A/C clutch will not engage unless the system has a full charge of refrigerant?

I just replaced my A/C compressor, drier and expansion valve along with all of the o-rings under the hood and want to make sure everything is hooked up right before I get it charged with R-134. But the A/C clutch won't engage unless I direct feed 12 volts to it (jumpers from the battery).

 

Low pressure switch will not allow it to run,,, DON"T force it to run, The R134 carries the oil without you will damage the compressor.

 

Thanks Gorn. I was just trying to make sure it would engage and that all of the wiring was still good. I did a bench test before I installed the compressor, so I know the clutch works.

I'll take her over to the local shop and have the system evac'd and refilled with the correct amount of R-134.