Mercedes-Benz Forum banner

1 - 20 of 51 Posts

·
Registered
MB SL600, MB 380SE, Suzuki Grand Vitara, 38' Chris-Craft, Volvo V70XC, and my own two feet...
Joined
·
4,131 Posts
What were the symptoms that necessitated replacement?
 

·
Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
Joined
·
8,759 Posts
Where can we get the slowed down DVD version :rolleyes:

Is the green area on the evaporator the site of the leak or had it dripped down from the corroded looking headers?

What do you think caused that problem to happen in the first place?
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,371 Posts
Did you ever thought of building a vacuum pump, from an old refrigerator pot?

I have two of them on the side. ;)

Regards.
aam.
 

·
Registered
1995 SL 500 2017 AMG GLC 43
Joined
·
935 Posts
Where can we get the slowed down DVD version :rolleyes:

Is the green area on the evaporator the site of the leak or had it dripped down from the corroded looking headers?

What do you think caused that problem to happen in the first place?
Not changing the filter and receiver dryer on a regular basis.
 

·
Registered
2012 350ML
Joined
·
383 Posts
Discussion Starter #6 (Edited)
What were the symptoms that necessitated replacement?
I bought the car in June of '07 and everything worked fine. Sometime in late June of '08 I noticed the A/C wasn't cooling very well and the R134 was low - but not empty. I charged it up with a shot of dye and we went on vacation - some 100 degree days in Tennessee and everything was working fine but a few days after I returned home I noticed she was kaput again. I had been poking around the A/C lines with the UV but didn't see dye anywhere. I added enough gas to get the system working again and ran it for 15 minutes or so on a hot, humid night. Move the car and inspect the puddles from the evaporator drains for dye and sure enough, it looked like a doom game under there. That was all the evidence I needed to start planning the change. The A/C had also developed a terrible, foul odor from the vents that was a result of the refrigerant oil providing a wonderful place for bacteria to grow. You've seen the pics of the evaporator - the mold is clearly visible there too.

All the green stuff you see here is dye that is in the oil.
 

Attachments

·
Registered
2012 350ML
Joined
·
383 Posts
Where can we get the slowed down DVD version :rolleyes:

Is the green area on the evaporator the site of the leak or had it dripped down from the corroded looking headers?

What do you think caused that problem to happen in the first place?
Everything you see that is green is dye that has leaked from the system. As you can see, its everywhere.

Here is what my research leads me to believe happened...

Mercedes has had a bad reputation with evaporator cores since the change to R-134A. Since Mercedes is usually the leader in adopting new technologies for their cars, this has been going on since 1989 or so. In fact, the 1989 R129 was the first ever production automobile to use the new R-134A refrigerant. Most American automakers didn't adopt it until 1994.

R-134A has some of the blame as its molecule is much smaller than an R-12 molecule. This means that it will leak out of a much smaller fault that will R-12.

Also, oils that were compatible with R-12 are not compatible with R-134A. A whole new set of PAG (Polyalkylene Glycol) oils had to be developed for use with R-134A. These oils have the characteristic of being extremely hygroscopic (which means that they have an affinity for water). Brake fluid has similar properties which is why you should discard unused portions and always buy a fresh, sealed bottle when you need it. The killer is that components of the PAG oil combine with water to form a compound that is extremely corrosive to aluminum and more so to the epoxy that Mercedes OEMs used to connect the tubes together with on evaporators made up through the end of the 90s. Any moisture that gets into the system provides a sure recipe for this corrosion to happen. Essentially, the aluminum becomes porous to the point the smaller R-134A molecule can leak out.

Some evaporators use a combination of copper and aluminum and these are problematic for a couple of reasons... First, ever tried to weld copper to aluminum? The joints in the evaporator are epoxied together not welded. This epoxy can fail over time or be attacked by the corrosive oil. Second, copper and aluminum have different rates of expansion and contraction. This puts additional stress on the joints causing premature failure.

Copper evaporator cores do have a benefit over aluminum cores in that they are resistant to the corrosive effects of the PAG oils and they are soldered or welded easily. My research indicated that it would be best to find an all copper core but I couldn't find one that didn't contain any aluminum. There were many recommendations for the ACM brand core which is solid aluminum but does not contain epoxy. They supposedly have a superior welding method to join the tubes. The only place I could find one was from Russ at b u y m b parts.com .

Some of the pics I took, especially the ones under UV exposure seem to substantiate the porous metal claim as you can see below. It looks to me like the original core (notice the date stamped on it?) was a solid aluminum core.
 

Attachments

·
Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
Joined
·
8,759 Posts
Thanks for the report and your findings Matt. If this is the case we all have this potential problem lurking in the wings :(

Re. the foul smell, you were lucky not to have got Legionnaires disease !
 

·
Registered
300SL-24 1992 White;BMW X3-3.0 E83 2005 Blue;190E-2.6 1992(sold); BMW 316-1.8 E30 1983(sold)
Joined
·
227 Posts
By the way, dose anyone have the idea of how is the interval of replacing the dryer of the AC system?
 

·
Registered
97 SL500
Joined
·
1,259 Posts
Benz is the leader. Has been using R134A since 1989 (way before americans), your benz is an '08 and still had a problem with R134A. Benz had 10 years to come up with a fix and they hadn't. I guess my wife's 07 will eventually have the problem.
 

·
Registered
300SL-24 1992 White;BMW X3-3.0 E83 2005 Blue;190E-2.6 1992(sold); BMW 316-1.8 E30 1983(sold)
Joined
·
227 Posts
...These oils have the characteristic of being extremely hygroscopic (which means that they have an affinity for water)... The killer is that components of the PAG oil combine with water to form a compound that is extremely corrosive to aluminum... Any moisture that gets into the system provides a sure recipe for this corrosion to happen...
That is the reason why I ask for the interval of replacing dryer. The dryer can contribute to absorb moisture.
Mine has not been replaced from new.
regards,
morris
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,371 Posts
Ehehe.
The real question is how do you get moisture in, in the first place.
The other is when you convert from r12 to r134 how do you get all the oil out?
Is the system leak proof.
See in a refrigerator the system is almost leak free.
Is it possible to build a similar system in the car?

Regards.
aam.
 

·
Registered
2012 350ML
Joined
·
383 Posts
That is the reason why I ask for the interval of replacing dryer. The dryer can contribute to absorb moisture.
Mine has not been replaced from new.
regards,
morris
Well, I disagree with Lee Wireless' earlier statement. Driers are not a maintenance item and I don't think you will find a service interval on them in the manual. There is no good reason to open a perfectly working A/C system just to change a drier. To do so only increases the risk of contamination.

You should, however, change the drier EVERY time you have the system open or whenever it has leaked off its pressure. The drier does three things... it filters the refrigerant coming through the system, it contains a desiccant to absorb any moisture present in the system, and it is a reservoir for oil. There is no way for any moisture to get inside a sealed, properly operating system and if it was evacuated properly and held for the recommended period of time prior to charging then there will be no moisture present or a minute amount that can be captured by the desiccant.
 

·
Registered
2012 350ML
Joined
·
383 Posts
Discussion Starter #14
Ehehe.
The real question is how do you get moisture in, in the first place.
The other is when you convert from r12 to r134 how do you get all the oil out?
Is the system leak proof.
See in a refrigerator the system is almost leak free.
Is it possible to build a similar system in the car?

Regards.
aam.
aam, did you know that propane is a nearly perfect retrofit for R-12? The molecule is also big and resists leaks. DOT has banned the substance from use as an automotive refrigerant because it is flammable. Doesn't seem to make sense when a tank full of gasoline is just a few feet away. I believe propane is also known as R-290. Look it up.
 

·
Registered
300SL-24 1992 White;BMW X3-3.0 E83 2005 Blue;190E-2.6 1992(sold); BMW 316-1.8 E30 1983(sold)
Joined
·
227 Posts
Thanks a lot, Matt.
In the last 5 year, I have done refrigerant make-up twice because of insufficient pressure. The workshop said it’s normal for A/C system to leak some after running a period of time, and he also recommended me to replace the drier next time of re-filling refrigerant.
Should I?
My A/C system has been running well except the re-fill, and I, like others, want the system to continue healthy through the time. Change to a totally new drier can last the A/C life, but has the risk of contamination, keep the old stock, could be another desiccant run-out risk.
That's my dilemma.

regards,
morris
 

·
Registered
1991 500SL
Joined
·
140 Posts
Great Job Matt. I don't mind saving some coin by DIY, but that's downright impressive! :bowdown:

So here's a question. My 1991 had R-12 right from new. The AC gave up not long before I parked it last fall & MB dealer had a look and said the system components are functioning OK, but will need conversion to R-134, so that is on the list for spring. I planned to have them do the job, but will they be able to remove the old oil and put in the new (proper) oil for R134? Or will converting the system just cause me corrosion problems in the next couple years?
 

·
Registered
2012 350ML
Joined
·
383 Posts
Discussion Starter #17 (Edited)
Great Job Matt. I don't mind saving some coin by DIY, but that's downright impressive! :bowdown:

So here's a question. My 1991 had R-12 right from new. The AC gave up not long before I parked it last fall & MB dealer had a look and said the system components are functioning OK, but will need conversion to R-134, so that is on the list for spring. I planned to have them do the job, but will they be able to remove the old oil and put in the new (proper) oil for R134? Or will converting the system just cause me corrosion problems in the next couple years?
I've read a lot of stories about guys who were completely disgusted with R-134 retrofits and guys who were completely happy with them. Your location probably would have a lot to do with it. A fellow in Canada (like yourself) would probably be more pleased than someone from say, Florida or Arizona.

That said, I believe the only real way to convert an R-12 system to R134 is to replace the entire system. Condenser, compressor, evaporator... everything. That's a lot of work and money and most owners would likely just let the A/C go on a convertible car.

The important thing to do when retrofitting is to get every trace of oil out of the system before you recharge. Not doing so would likely cause compressor problems - not corrosion problems. Most of your oil is in two places - the compressor, and the drier. The system has to be thoroughly flushed before recharging and the compressor be rotated or disassembled to make sure all the old oil is out. Every seal and o-ring should be replaced also. The older black rubber seals are incompatible with R-134.

There are a lot of guys with SECs and Es from the late 80s who have converted. You should look up some of their experiences here and on mercedesshop.com before you take the plunge.

Out of curiosity, do you know the reason why your A/C quit and needs conversion? It will likely need repair before it can be converted. Has the dealer outlined their procedure and what parts they will replace? Have they created any expectation of what vent temps you should expect after the conversion on a 80F day? Can you share the expected cost to have this done?

I knew there were a few R-12 R129s out there because the manual references them. Is your car imported from somewhere else or is it a normal North American car?

If you do retrofit, you will probably only see 55 degree (F) vent temps which would probably keep you cool on a 80F day. R-134 does not have the heat carrying capacity of R-12 and requires a larger evaporator to provide a similar cooling effect. My vent temps are in the 38-40F range with 35(F) common at the evaporator.

The corrosion you are worried about is a simple function of how much moisture is in the system after it is charged. Drawing the sealed system down to -29 in of vacuum causes all the water in the system to boil off and it should be held there for at least one half hour. I pumped mine for 2 hours.
 

·
Registered
2012 350ML
Joined
·
383 Posts
Discussion Starter #18
Thanks a lot, Matt.
In the last 5 year, I have done refrigerant make-up twice because of insufficient pressure. The workshop said it’s normal for A/C system to leak some after running a period of time, and he also recommended me to replace the drier next time of re-filling refrigerant.
Should I?
My A/C system has been running well except the re-fill, and I, like others, want the system to continue healthy through the time. Change to a totally new drier can last the A/C life, but has the risk of contamination, keep the old stock, could be another desiccant run-out risk.
That's my dilemma.

regards,
morris
Morris, the bottom line here is that your system has a leak. Would you be satisfied if you had a flat tire every month or so and a shop told you it was normal and you should just fill it up? (actually, they do kind of work that way but most tires will hold pressure for many years) I don't agree that its normal for a system to lose any of its refrigerant over any period of time.

Its probably impossible for you to know but if your system bled down to outside atmospheric pressure, you should change the drier. Every temperature change and pressure change moved air and moisture in and out of your system.

My wife's explorer had a nasty habit of bleeding down to about 2 bar pressure and would quit leaking. I finally found the leak (pressure switch) and got it fixed. I never vacuumed the system because it was never open to the air and was never discharged to atmospheric pressure.

So I guess my final advice would be to change the drier, but also have the system leak tested and fix that leak before recharging again.
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,371 Posts
aam, did you know that propane is a nearly perfect retrofit for R-12? The molecule is also big and resists leaks. DOT has banned the substance from use as an automotive refrigerant because it is flammable. Doesn't seem to make sense when a tank full of gasoline is just a few feet away. I believe propane is also known as R-290. Look it up.
Yes I am very much aware of propane.
Not the one used in bbq, a cleaner more dry propane.
And there is no need to replace the oil etc. ;)
And is dirt cheap.

But us you know for legal and political reasons, prefer to be quite, sometimes. ;)
Many years a go the transportation companies were flushing R12 in trains, and trucks to keep things
frozen with out recirculation just (Venting it out. )
It was cheaper to dump it in the atmosphere then running equipment.
Many manufacturers it starts with a letter D and making billions of profits.
Factories were getting old,,,, people were getting accidentally killed.
OK Albert, Shut up all ready.

Most leaks are at the compressor shaft seal.
You were the unlucky one to have it at the evaporator, s*t happens.
As far as replacing O rings, hoses on converting from R12 to R134A.
You don't have to, the weathering builds a coat on the inside so it safe for a while.
You noticed I said a while.
All systems will leak.............................

Regards.
aam.
 

·
Registered
1991 500SL
Joined
·
140 Posts
Out of curiosity, do you know the reason why your A/C quit and needs conversion? It will likely need repair before it can be converted. Has the dealer outlined their procedure and what parts they will replace? Have they created any expectation of what vent temps you should expect after the conversion on a 80F day? Can you share the expected cost to have this done?

I knew there were a few R-12 R129s out there because the manual references them. Is your car imported from somewhere else or is it a normal North American car?
The pressure in the system is down (I think to around 35 psi???) and with it being a 1991, I guessed it is just due for a re-charge. Problem is you cannot get R-12 in Canada anymore so garages are changing over to R134A. I know that it is not as effective as the R-12 in cooling, but what choice do I have? I do occasionally make runs south to areas with 90 -100 F temperatures so I would like to keep the AC working. There is a refrigerant out there that is supposed to be an alternative to R-12 or 134, but I don't know much about it. Here is a picture of the refill kit you can buy here for about 50 bucks, but I'm a bit nervous of using it. The one pictured is a brand called Red Tek, but ther are others. A/C systems are not exactly my strong point and I don't want to save a couple dollars on one side and screw something else up in the end. (MB quoted $550.00 for the conversion, but I will have a lot more questions for them from your previous post).

As for the car, the info that I can find from the VIN lists it as a US sold car, (dealer 705) however I bought it couple years ago from a dealership who imported it from Japan. From what I have found it is 98% US parts, with a couple Japan specific features ie: headlights, side 1/4 panel blinkers.
 

Attachments

1 - 20 of 51 Posts
Top