ChuckinTucson

My sister-in-law has a '05 C230K. She has a habit of shutting off the A/C when she parks the car overnight. in the morning she starts the car. Everything normal. She turns on the A/C everything normal. She shift to reverse to back out of the driveway and there is a squealing noise coming from the engine compartment. She shifts to drive, no more noise. Only happens in reverse on warm mornings with the A/C on. I'm thinking compressor pulley. Any other thoughts.

Jhartmann3

Before replacing AC pulley, make sure serpentine belts are good and belt tensioner is good. AC compressors aren't cheap, just had to replace mine.

VVF

No-no-no, that's definitely the alternator overrun pulley
I had the same exact issue with the noise etc. Scared the crap out of me.

The problem is, with the extra load on the engine the idle is somewhat unstable.
However the alternator is large and inertial, it tends to keep spinning at whatever high speed the engine fluctuated to. With the overrun pulley seized, this makes the serpentine belt skip and slide, hence the noise.

If she doesn't get it fixed, the AC pulley will break and she will have to replace the AC compressor.
Car probably has about 100-120k miles?

LILBENZ230

The C230K cars are all very rough in reverse.. I'm inclined to agree here with VVF, if the alternator pulley bearing goes out it is adios, sayonara A/C compressor. The compressor is also a swash plate design, always spinning so get it into the shop ASAP.

Carsy

Please explain to an old bloke why the air-conditioner will be damaged if alternator overrun pulley fails ? Thank you.

greenv

If the alternator overrun pulley fail a big vibration was observed in the pulley. Due to this vibration the air-conditioner compressor clutch gone.

VVF

Solid pulley == seized alternator pulley