Compressor pulley bearings that keep the A/C drive smooth.
These bearings support the compressor clutch and pulley. Wear can cause a whine or rumble that changes with A/C load. Match the bearing by its inner and outer diameter and width, or cross reference the compressor model. Inspect the pulley face while the belt is off. Press the new bearing in using steady, even pressure so the housing is not damaged. A correct bearing helps the belt run quietly and reduces the risk of seizure during hot weather.
A whine or rumble at the front of the engine that changes with A/C load.
Many pulleys allow bearing replacement without changing the full compressor.
Most pulley services can be done with the system sealed, depending on the vehicle.