ODIOUS

Im going to be replacing my AC components on my 11' 4matic this spring.
2 years ago the AC compressor went out and I replaced it myself.
The job was pretty straight forward and I took me a day at a leisurely pace to do it all.
Bcos the compressor simply stopped working (wouldnt engage when current applied) rather than seizing up I thought it did not meet the level of catastrophic failure.
So I replaced the compressor and drier leaving the expansion valve and radiator in place and did not bother to flush the system.
I vacuumed out the system, used the proper amount of refrigerant (knowing that there would be a little residual still left in the line) and filled it with the proper refrigerant as specified.
Everything worked very well for over 2 years. Then one day the compressor seized and tore the accessory belt apart in the process.

The compressor was manufactured or rebuilt but UAC and it came with a 2 year warranty.
When you turn the pulley it only rotates from 10-2 and stops.
Ive seen some videos of the internals of these pumps and i imagine of the the large ball bearings have popped out out place.
Bcos it was fall when this happened I simply got a shorter accessory belt and bypassed the AC compressor.
Its a matter of debate whether I did anything wrong other than using an inferior aftermarket part.

But now that the weather is warming up I'm going to go back in and redo the to the very best of my ability.
This includes changing and replacing the radiator/drier, both expansion valves and compressor with OEM parts.
Doing a full flush of the pipes and orifices with a AC system flush kit and maybe even looking into do a nitrogen gas flush/purge procedure when it comes time to evacuate the out the system.
All this will certainly not take a leisurely afternoon to do but I am hoping with some advice from anyone who has done this on these larger vehicles will help with the process.

Im in the process of ordering all the parts i will need for the operation.
Any help/advice you guys and send my way would be greatly appreciated!

ODIOUS

Would anyone happen to have the procedure for removing/replacing the AC condensor?

Thanks in advance!

ODIOUS

Another question for anyone who may know... where exactly would the 2nd expansion valve (for the rear AC system) be located?

Does anyone have experience with installing/using an AC Inline Filter Kit? I think I want to install on permanently on my system.

ODIOUS

So i began the overhaul today after getting the last of all the parts parts delivered last week,
This wont be a walk through but rather a few pointers and musings that I have come across.

First and foremost: I was relieved to find that the bumper did not have to come off in order to remove the AC condenser. Nor did I have to disconnect any lines or loose any fluid from the radiator. The radiator carriage allows for a remarkable amount of play once the front support is removed. You WILL, however, have to removed the 4 bolts holding the air baffle to the radiator assemble and the front central console. I circled their locations on the attached picture. The air baffle is a single large piece on the W251 unlike other models. If you have not seen the baffle before you will not know that the bottom two bolts are there. They are accessible from the bottom and having the vehicle elevated is mandatory. I had mine up on a set of Rhino ramps.
Once the baffle is free you can lean the top of the radiator forward almost touching the engine. Pulling the baffle back the opposite direction gives you just enough clearance to maneuver the condenser out of the assembly. Note there is a single bolt holding the AC line block to the side of the radiator assembly. This will have to be removed before the condenser will be totally free. Installing the new condenser is same steps in reverse. Be sure to lean the radiator forward as far as it will go. The AC lines of the dryer will not make it in or out otherwise.

Next up is the location of the main expansion valve (TXV). There is a removable shield on the engine bay wall that needs to be removed to have access to the TXV (you'll need to remove the engine air box as well). Its held together by 2 bolts and needs to be slid up to remove. Once removed you will have clear access to the TXV. The 2nd TXV is located within the cabin deep within a 2nd row console. I believe you would have access to it by taking the interior apart.

Im also taking the added step of adding a HIGH SIDE INLINE FILTER to protect the system from any debris that I might have missed. Using all new o-rings as well as planning on adding ACEP Lubricant Enhancer to the mix in the hopes that it will make things easier on the system.

Lioninstreet

I went thru this process with my rear AC R350. Turns out the compressor for the 3 zone system has been discontinued in the US and the PN supersedes to the two-zone compressor. It appeared to hold less oil so there must be some kind of difference. I went thru several days of hoop jumping, even calling Denso UK to find the correct PN both OE as well as new aftermarket.

ODIOUS

Thank you VERY much for this comment. I didnt realize there was a switch from 3 to 2 zone compressors. I didnt take note of the part number of the compressor when i took it out the first time.
i just picked a compressor that was listed as compatible. Your heads up on the varying oil quantity is an eye openner and i will do my due diligence on what is supposed to be in there. I know these compressors come prefilled with the appropriate amount of oil but i better find out what exactly that is.
Ill check my VIN for the part number of my original compressor and work my way backwards. I was planning on installing the compressor tomorrow as i had done some flushing today.

Lioninstreet

Maybe I can save you some time. Give me a day or so to dig out my research and I'll post it. I was never really able to discover the internal differences, but I do remember when I started looking into finding the replacement compressor that the two zone and the three-zone compressor held a different amount of fluid. From there I went OCD on it.

ODIOUS

Thanks again. Look forward to hearing about what you can dig up.
i started looking at old notes of my own and found itemized estimate an independent shop quoted me for the AC work. I changed everything out myself but im noticing I didn't use the BF Frigi-Quiet that they were going to use. Im womdering if its just like the enhancer additive i plan on using...

I was looking at the compressor i bought (Mahle Behr ACP354000S) and in the fitment notes it says its for R1234yf refrigerant. Makes no mention of r134a. Not sure what that is about but id like to assume i can use it as intended by MB for this application.

Lioninstreet

Here is some of what I dug up on the tri-zone vs the dual-zone AC compressors when I had to change mine:

1) Per the sticker on the OE compressor that was on my tri-zone '11, the Merc p/n for it is 002-230-55-11. There is also a Denso sticker showing it was manufactured in Germany. While attempting to source it from Denso, I found that Denso USA has discontinued the tri-zone compressor, but Denso EU has not.

2) When searching for the same using a Merc on-line parts catalog and the VIN for both an '11 & '12 tri-zone (I've owned both) the below us what currently pulls up:
002-230-52-11 - Without rear ac. Gl450. Ml500, ml350. All. Gl550. Exc.Auxiliary A/C. Ml550. R350. R500. 3.5l.
002-230-55-11 - Shows discontinued.

3) Denso - (note these are the European part numbers but are used to illustrate there is a different pn# for the tri-zone compressor).
a) Per the '21 & '14 Denso EU catalog the pn's for the tri-zone compressor is DCP-17055 / 471-7055
b) Per the '21 & '14 Denso EU catalog the pn's for the remaining R-Class Compressors are different pn's (DCP-17058. 17059, 17062, 17063, 17065)
c) Per the current Denso US on-line catalog, the only Denso p/n for the R-Class compressor is 471-1594 (which replaces 471-1436). I was unable to cross reference to the EU pn#.
d) The current Denso EU catalog shows 3 compressors available. The specified 17055 tri-zone compressor has a 140 ml capacity vs the 100 ml capacity for the other 17058 & 17059.

4) Aftermarket Compressors - Only one company was found that specifically specified a different p/n for a tri-zone system
a) GPD - Linky to 2011 R350 A/C parts PN# 6512217 & I contacted them to confirm application.
b) 4 Seasons has two pn#'s but no one there was able to confirm differing applications.



I ultimately went with the GPD as it turned out to be crazy expensive to have one shipped stateside by a euro Denso Distributor.

Also, If you plan to keep the R for a while don"t forget to also replace the serpentine belt, belt tensioner, and idler pullies while you have everything apart. I actually had an idler pully go bad on me on a different model Merc in under 50k miles.

Lioninstreet

I believe the second expansion valve is behind the driver's side rear AC vents. Never used a filter kit.

ODIOUS

You went above and beyond the call of duty on this one @Lioninstreet
plethora of information here. From what you have gathered i think the differences in the compressors were simply their capabilities. The 3-zone variant had an oil capacity of 140 ml where the 2-zone ones were 110 meaning internally it had more 'horsepower' if you will to accommodate the extra load of the added zones. Everything else from the spec sheet were the same. Somewhere along the line MB decided that the 2-zone could handle the load of 3-zones. At least they thought the failure rate would be equal or less than the current rate.

The replacement pump i ordered is a Mahle Behr ACP 354 000S with 110ml oil capacity.


I spoke with Mahle tech support today and they gave me a good bit of information. Most importantly while the compressor comes prefilled with some amount of oil it is NOT prefilled to any vehicle's specifications. Rather the oil that they add to the pump is merely to prevent rust and corrosion. You are to empty the oil out and refill the compressor with the right amount of fresh compressor oil for your vehicle (dont mix oil with new). For future reference 1 oz of PAG46 = 30ml =30 grams. This should make measuring the right amount easier for ppl. They also suggest checking ALLDATA.com for your specs like capacities and filling volumes as other sources (even their own) can often be wrong or missing vital details and distinctions. For instance... he told me that ALLDATA specifies 120 cm3 (ml) rather than 110. Removing the prefilled oil was a long drawn out processes. Not as simple was tilting the compressor and letting it drain out. Several turns of the pulled (i used a drill with a socket to speed up the process) and tilting the body back and forth was required. Just when you thought you were done... more oil would come out. In all i removed 60 ml from the pump.

They recommend not to use any additives like the enhancer i wanted to add or even the BG Frigi-Quiet. They classify them as 'contaminants' and they believe it will ultimately do more harm to the compressor than good in terms of its longevity.

The 2nd TXV is located in the rear AC unit in the center console between the two front bucket seats. Its connected directly to the rear AC condenser. Labelled #50 below.

But whats interesting is this TXV has a built-in solenoid which (i believe) closes the valve completely when not in use. This actually prevents you from flushing that condenser without its complete removal. The supply lines that runs to this rear unit is tee'd off from both the high and low side inside the engine bay. The diagrams in the EPC do not show this. I have a better appreciation for the work involved for shops to do this job if they were to do 100% by the book.

The inline filter I'm adding should catch any large debris that i missed by not being able to clean out the rear condenser.

ODIOUS

Installation of the compressor this week went well and without incident. System is blowing nice and cool in all 3 zones and the compressor seems to be working well. I installed a new serpentine belt, pulley and tensioner as recommended earlier. I did end up using the Enhancer additive against Mahle's recommendations however. The promised benefits of improved efficiency for this setup (which seems to use a 2-zone compressor or a 3-zone system) was too enticing to pass up.

I would like to do a DIY refrigerant recovery some day down the line and check the inline filter i installed for debris but this is for my own edification actually not necessary as the filter is designed to be left alone. If i never see have an issue with the system i'll consider it cheap insurance that paid off.

Im looking to take the old compressor apart to try to determine the cause of death. I was surprised to hear something metalic rattling inside. From my initial research there seems to be half moon shaped bearings in these compressors and they are known to pop out of their seats. If this is the case it would be nice to know what the cause was (poor quality parts, low oil, contaminants, etc). The system was was fully snd properly charged with refrigerant and blowing cold air when it died.

ODIOUS

I took a few minutes to teardown the locked up compresssor and I found a few interesting things:

1) just as i suspected i found that one or more of the bearings had come out of its slot(s). This is what was physically preventing the pulley from rotating.



2) In additiin to that the plate (race?) which ithese bearings ride on was heavilily worn in a few places (copper colored marks where steel used to be).


3) the pistons suffered the most. Deep gouges on some where the bearings ripped off or ripped past them (L+R is bad; center is good) and the surprising appearance of bubbling on a majority of the piston's coating.



4) everything was covered in an fine oily soot which i have read is called black death. This is the stuff we aim hard to flush out with solvent. I did not see or feel any large debris, particles or metal shavings however.

ODIOUS

Last thing i want to mention for anyone doing this repair is to be sure to check you high pressure hose for defects. Mine had a bulge on both ends near the .metal crimp points. I dont know if this is normal wear and tear for a 200k mile vehicle but there was no good reason for me not to replace it. I was able to get an OE used replacment for $20. New aftermarkets can be had for around the same price but i prefer to go used originals rather than new from a manufacturer i do not know.

Good luck and hope this helps.

Lioninstreet

Very nice @ODIOUS Good tip on the hose check. It's easy to overlook the little details that nail a foot to the floor when you miss them