A squeaking air conditioner is alerting you to a problem in the system. There are several possible causes:
Low on refrigerant
The compressor must work harder when the refrigerant level drops. This leads to overheating, which causes a squeaking noise.
Only a licensed tech should install refrigerant, which is toxic.
Overheating, incidentally, also can occur when the bearings begin to wear down. Again, the squeak is a warning sign.
Over time a blade can begin to wobble due to wear and tear. This creates a squeak, which often can be rectified by tightening the blade.
Dust and debris can accumulate on the fan blades and other components, slowing the system and triggering a squeaking noise.
Premier HVAC techs are both experienced and well-trained, attending seminars to stay updated on the latest technology.