328i noise when engaging AC

[bluefish7]

I'm wondering if anyone else has ever had a whining noise after turning on AC, sound is similar to a failing power steering pump when turning, but seems to ramp up and down with the rpms. Something going with the AC clutch? Seems to be charged correctly as cold enough. Thanks

[megastihl]

I too have a noisy A/C compressor, but mine doesn't whine but sounds like scraping metal when engaged. But it's still cooling and running fine for years now so unless it goes bad I won't replace it. Could be a bearing in your case.

[MarcoZandrini]

AC compressors need a specific amount of special compressor oil. Has the AC system in either of your cars ever been recharged? If it has then the system is low on compressor oil. The fix is to take the car to a professional AC shop. Here’s what needs to be done:
- evacuate the system
- replace the dryer (the desiccant bags inside the dryer break)
- perform a 30 minute vacuum test
- refill with the correct amount of R134a (these AC systems are finicky about the amount of refrigerant)
- add the proper amount of compressor oil
- test.

[bluefish7]

Thanks, I am EPA certified and trained in refrigerant, just have only recharged cars and never taken the compressor apart. Is this a reasonable DIY job?

[MarcoZandrini]

The compressor is a relatively simple device. Basically there are several (the number 6 sticks in my mind) pistons that are pushed into their respective cylinder by a rotating plate. The plate rotates as its driven by the engine via the AC compressor belt. Of course, there are bearings. You might be better off buying a rebuilt compressor.