When I changed my serpentine belt, I went ahead and tested, spun them by hand, all the accessory pulleys to determine the condition of the bearings.

Vehicle is a 99 ML 320 with 117K miles.

I found all were ok except the idler pulley which felt and sounded like it had no grease in it at all and the bearing in the A/C pulley for the clutch, which made a rumbling sound.

I put in a new idler pulley, they are cheap and very simple to change.

As far as the A/C clutch goes. I removed the spring plate, snap ring that retains pulley and pulley. I then removed bearing from pulley. The coil is not removed. My bearing is a Koyo part# DAC355222RR9D, it measured 35mm x 52mm x 22mm. That size is commercially available.

Below is a picture of what I removed. This is done with compressor mounted in vehicle.

I’m thinking that by changing the bearing before it fails will help extend the life of the compressor. The MSRP on the clutch from dealer is $730. with the MSRP for the compressor being $945.

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