Rattling sound coming from PS pump/AC Compressor area
 

I just noticed last night that there's a distinct rattling sound audible through the open sunroof, almost like marbles rattling in a can. So far, all I know is that this sound is coming from the driver side front of the engine compartment, almost as if from either the power steering pump or the AC compressor. I'll probably do more troubleshooting tonight, but thought I'd pick the wise minds on this board before I start. The only thing I have planned is just to check the PS fluid level. Any suggestions on what else?

Probably going to have to narrow it down with the hood up and engine running before anyone will be able to help. Which car (Model & Year)?

More details...
 

83 300TD

I checked briefly last night with the hood open and engine running. I'm 90% sure it's coming from the vicinity of the PS pump and AC compressor. What are symptoms of either failing? My first thought was that one of the bearings on either component was heading to the grave.

Also checked for loose parts vibrating against each other, or the fan brushing against something - didn't find anything. AC has been out for some time now- my suspicion is that it just needs a freon charge (there's been a known leak for a while- compressor will still engage if you jumper across the freon pressure switch).

Don't forget to check the AC bracket mounting bolts. There are three of them. Two of mine broke and rattled in the bracket making a noise similar to your description.
Richard

Check your A/C belt. See if it hasn't dropped some chunks. Mine made the very same noise when that happened. Does it quiet down when A/C is off and get bad when its engaged?

AC pulley bearing at the clutch will usually rattle most when the compressor is not engaged and less when the compressor engages. Worth checking the bearing there as it is not an uncommon failure.

Thanks guys...
 

I'll be sure to check the belts and mounting bolts. The compressor hasn't been engaged in over a year because of low freon, so I can't compare the sound with the AC on and off.

Invest $10 in a mechanic's stethoscope. DON'T touch any moving parts with the probe or your ears will ring for an hour.

If you've never used one before. You will be amazed.

One thing you can do to isolate the source of noise is to use a long 3/8 extension bar (or similar item). Put on end of the bar on the suspected component. Put the other end in your better ear. The bar will transmit the sound like a stethoscope. Just watch out for moving parts like belts, pulleys and fans.

Or better yet, if you know any nurses, invite one over ask her to bring her stethoscope.

What about the vacuum pump?

Well if you have a R4 compressor, my bets on it. After 2 rebuilts that had the same marbles in a can sound within a year of installation, no more rebuilts for me.

you need to isolate the sound. The vaccum pump can also make a rattle but it is more like a regular loud ticking like a loose lifter.

My 300CD has an inoperative AC system. The compressor is shot and the belt is disconnected. Shortly after I bought it I noticed the same kind of sound.

The compressor had worked loose in its bracket. Made a heck of a racket. I'd check that first. If you idle the engine and shine a bright light down on the AC compressor you'll be able to see if its loose.

I had a sound just like that on my SD, the compressor/A/C don't work anymore, but it still had a belt (in poor shape) and whenever the engine was at around 1,200-1,300 rpm I'd get this rattling noise, it happens to be the rpm at 25-30mph so it was quite annoying in the city. I checked and checked and finally figured out it was the clutch plate on the front of the A/C compressor vibrating at that particular speed. I cut the belt off, and the sound is gone!! :D Someday I hope to have A/C......thats a day a looong ways away.

I finally traced the rattling sound- it's coming from a plate on the front of the AC compressor clutch. There's what looks like a ring on the clutch facing the front of the car, rattles pretty bad at around 2,000rpm.

So, who knows what this rattling plate is, and how it can be fixed?