Clunking noise from AC compressor
 

I completed an AC overhaul this week but now the compressor is making clunking noises. When I leave the air running but put it in the EC mode the clunking noise stops.

I had the dealer put in a new receiver-dryer and I put in a push button control and then the dealer pulled old refrig out and put new in. It has never made this noise before now.

Looks like compressor was replaced in 1994. It is the cheaper one.

compressor never runs on the e/c mode so you wont hear the noise while on e/c, I would check on the high side pressure to make sure it is not overcharged. also check everything around the compressor to make sure the noise is actually coming from it. Sometimes people charge liquid refrigerant through the low side of the system and allow too much liquid into the system, that liquid refrigerant has to boil before it gets to the compressor otherwise it could have devastating effects on the comp since liquid doesn't compress. I'm not sure this is your problem but liquid in the comp can bend the valves and cause other problems without necesarily detroying the compressor. Hope is something simpler!

". Sometimes people charge liquid refrigerant through the low side of the system and allow too much liquid into the system,"

Any liquid refrigerant into the low side of the system is too much....The first thing it hits are the reed valves...and they go Kaput.....

There is no mechanism to allow for the boiling once it moves downsteam of the evaporator. Liquid refrigerant is always installed in the high side.

Yes, it could be overcharged, but if any bolts are loose it could cause the noise. Check the bolts for tightness.

Good luck,

Although I dont do it, if done carefully it is possible to charge liquid through the low side depending on the system and wether it has a liquid expansion reservoir before the compressor and you charge it in small burst, what I meant was that people just open the valve and let a rush of liquid in and that's it for the comp. I do agree that any liquid in the low side is too much but in practice that's not what happens :D

This is a Mercedes Diesel forum.... do any of our cars have that ?

I suspect not... and we have enough trouble getting people to believe that the rules should be carefully followed anyway.... people accuse us of trying to make it ' mysterious' when we are just trying to emphasis how important the rules are to longivity in a very harsh enviornment ( inside the system)....

And if you knew that a " liquid expansion reservoir " was needed to make the statement correct and safe for lay readers it should have been included in that post..

"but in practice that's not what happens " --- how about describing where you see this happening... and tell what the advantage is... compared to sticking it into the high side as the books suggest ?

It very much depends on the particular compressor. Some make and model compressors are very tolerant of this and some, such as the old York and Techumsehs will break a valve at the least little introduction of liquid.

As a general rule, just don't take the chance. If the system won't take gas, then warm the cannister, or if using cans, lower the can into a bucket of lukewarm water.

Good luck,

Maybe a loose belt. This may sound too simple, but best to eliminate the simple ones first. My compressor sounded like marbles rolling around in a coffee can. It cooled great, but at idle I could hear it above the engine noise. Thanks to a suggestion on the ShopForum, I tightened the loose V-belt and solved the noise problem. Be aware that my belt was not extremely loose, but just enough to cause the noise. Hope this works for you.

Hmmm
 

They recovered the system, replaced the dryer and recharged refrigerant.

Point #1. If they did a fast recovery = system oil loss.
Point #2. When you replace the receiver dryer = system oil loss.
Point #3. It is possible the oil loss was not replaced.
Point #4. It is also possible the oil loss was replaced with too much oil.
Even if the system pressure looks right, if the oil loss volume was filled by extra charge = lubrication loss + system over charge = added stress and wear on the compressor + system cooling capacity loss.
Excess oil = compressor noise + cooling capacity loss.

This is all guess work without further data.

This is how we do it in the OEM climate control laboratories.
#A. Recover the system slow.
#B. Remove and drain compressor.
#C. Remove receiver dryer.
#D. Flush the system.
#E. Fill compressor with correct oil charge.
#F. Install compressor.
#G. Install new receiver dryer.
#H. Charge system with 110 psi nitrogen for thirty minutes = leak check.
#I. Vent nitrogen charge and vacuum system for thirty minutes.
#J. Charge system with fresh refrigerant.
At this point you will know the oil and refrigerant charge are right.

Roy, how do you do a leak check on nitrogen? Do you simply look for the system to hold pressure? If it does not hold, how do you locate a tiny leak, if you are leaking nitrogen??

:GRIN: easy
 

Nitrogen is for gross leaks, but worst case for tough to find leaks = add half ounce of refrigerant to system for detection.

Most leaks are gross leaks.

Thanks, sounds like the ticket. :cool:

Hey all am saying is that people don't always do things the way they're supposed to and some systems do have "liquid expansion reservoirs" when I mentioned this I was referring to people in general and not diesel owners in particular.
"how about describing where you see this happening..."
I "see" it happening all the time when people hold the can of refrigerant sideways and start shaking it as opposed to holding it up where only gas will flow out.

The clunking can be as simple as a belt that lost a chunk out of it if its not new. My W116 did the very same thing...I though tthe compressor was about to self destruct and then I noticed the belt...then problem solved.

boy, that's a good thought. makes a lot of sense, because the noise is load related on the system. BTW, BHD you win the prize for most improved Avatar. That is simply beautiful and mesmerizing. :)

Well I was getting tired of the old one......... :D

Wasn't AC compressor
 

Sorry guys and gals,
It was not the AC compressor. The power steering pump failed today. The noise was coming from there it seems now. It got really loud and then stopped suddenly. PS went out immediately. It was a salvage yard pump that I rebuilt myself.

Lucky I still have the original and the new seals. They got dropped off at the local hydrolic shop today.

I think the dealer did leak test
 

The dealership did leak test because they added dye to the system. I never got a full explanation, but assumed the dye was to check for leaks.

Enlighten me. :confused:

THe dye they put in floresses under ultra-violet light....and you'll see it where it leaks..

we use nitrogen at diesel school, filled it up and spry everything down with soapy water...any leak will bubble up immediately