My ac slowly stopped working ( never worked great )

So i decided to re-fill the freon, when i filled it it worked for a few minutes then a whining came from under the passager dash. Does this part need to be replaced or could there just be air in the system

 

Maybe you have a leak.

 

Air and moisture don't mix well with refrigerant in an A/C system. If the system was completely empty of refrigerant due to a major leak, then you must first fix the leak, evacuate the system, and then recharge the system to achieve the proper refrigerant pressures on the low and high sides.