compressor knocking-how much time?

[RG5384]

how much time do i have on a knocking compressor on an 83 300SD? I know it's the compressor, but dont know anything else. It isn't rythmic at all, and is inherintly only on with the a/c, if i push the button to EC the knocking stops. It's slightly noticable inside the car, and very noticable outside. Other strange thing is, it only happens sometimes, it's not a guaranteed thing. Of course, everytime i take it to my local indy to check out it stops I remember this problem last summer as well, and it's lasted one year so far(with minimal usage, i actually like to be able to accelerate!) thanks
Ryan

[jbaj007]

I would disconnect the two prong elect. connector to the compressor clutch now before the compressor fries. If the A/C compressor (even the Harrison R4) seizes it can give the whole system "Black Death" (small particles throughout all the components in the sytem). This means a full system flush, replace expansion valve (a risky job at best) plus the compressor and dryer (which you'd do anyway). A knocking R4 means it is or was at one time very low on mineral oil (assuming R12 refrigerant) usually from a leak that was just "topped off" over the years without an oil charge. I'd check the clutch to make sure it's the compressor and not the clutch, but it's usually the compressor. R4 rebuilts are relatively cheap, but get one from an A/C parts supplier or FastLane/MercedesShop; not from Autozone or Pep Boys (they don't call their rebuilts "Four Seizens" for nothing. Good luck.

[RG5384]

ooooh man! thats not what i wanted to hear AT ALL. crap. That sucks. thanks for the reply
Ryan

[RG5384]

well no luck on rebuilt on fastlane or performance products, i forgot to mention i had them add oil last time it was charged, and it is R34(or whatever the updated one is, ends in 34, maybe W34?)
thanks again
Ryan

[RG5384]

crap, i wish i would remember all this stuff at once, i'm wasting so much bandwidth here..... Anyway, the car also only does this at idle, or at least that i've noticed. It goes away with speed. I'm kind of leaning towards the clutch. If it was the actuall compressor wouldn't it do it all the time reguardless of RPM etc? The clutch i can see knocking intermittantly, pullys etc are very annoying at times. How do i tell the differance?
thanks
Ryan

[jbaj007]

If you disconnect the elect. connection and the sound goes away, it's probably the comp. Since it's only on with the A/C (clutch intermittantly engaged according to pressure) I'd expect this. If the sound is still there I'd think otherwise.

Might just be the clutch, clutch/pulley bearing assy. Might try freeing the belt from the pulley (loosen 3 bolts in rear of comp. & then loosen adi nut on top left) and seeing if the pulley assy. rocks when you shake it.

R134a conversions require different oil (PAG/ ester) than I mentioned in first post. Sorry, didn't know you'd gone 134a.

[jcyuhn]

I put a cheap remanufactured R4 compressor in my old 300D in, uh, 1994 I think. It started knocking in about 1997. I just turned up the radio. In 1999 I sold the car to a friend, telling him the A/C was probably going to go out. It finally did - in the summer of 2001. So my experience is these things can last a long time while making a pretty good racket.

BTW, try tightening the mounting bolts for the compressor to the bracket. If they are even a little bit loose, the compressor will rattle like crazy. I had this happen and couldn't tell it wasn't an internal problem - found it by accident.

[Gary F.]

Are you sure they added oil at last recharge.??. I guess you will never know. Any way go buy some oil compatible to 134a coolant and add it to you system, it comes in 2 oz containers. Cant hurt and may save your compressor.



Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a life time.

[RG5384]

posotive, i MADE them add more oil, it was knocking right after they did it and i MADE them add oil even though they were grumbling bout it the entire way. SOmethign about old oil doesn't come out or something, it did make it much quiter, but it's coming back. I guess i could try more oil again
R

[Gary F.]

If you have a leak in your system you will lose oil. Generally you can find where your system is leaking by looking for oil spots on your coolant hoses, generally at connections. Make sure the connections are tight, but do not over tighten. Use two wrenches so you don't twist the lines.