I just acquired a 600SEL and noticed on the service records that the AC evaporator was replaced/fixed last year. Now, I hear horror stories about this systemic maintenance problem.

Question: Because the evaporator problem was fixed by an authorized MB dealer, will the same problem (leakage) recur down the road or did the "repair" improve upon the original design such that the problem with the evaporator will likely not occur in the future? In other words, are we doomed to repeat the same evaporator failure down the road?

Your car was just unlucky. The odds of lightening striking in the same place twice are not high.

We read such horror stories and it's easy to get the idea that every one of these will fail. In reality when there is a weak spot such as this, it means that 15% or 20% of production are failing.

Odds are the system will be fine from now on. If it does leak, it will probably be something else. ANYTHING else that could leak would be a small problem compared to the evaporator.

Enjoy your a/c, be happy and sleep well.

Have a great day,

I'm going through AC woes right now with two different cars. I'm finding out that one need to do some preventative matinance. I'm hearing that one should vaccuum the system anywhere from 30-60K intervals. One also needs to replace the dryer (60k?) on occasion as well. It seems that leaks in the evaporator are caused by contaminants getting into the system and eating away the evaporator.

NEGATIVE on what you "heard."

Evacuating a perfectly good working system on a regular basis introduces a much greater chance of contamination and problems than just leaving it alone.

If the system is tight and was properly evacuated and charged, there is no way that any contaminants can get into the system. Even if there is a leak, there is no way contaminants can enter unless it is on the low side and gets so low on refrigerant or has a restriction that causes it to go into a vacuum.

The evaporator leaks can occur due to two basic causes. The first and the one that makes these evaps fail more than others is the fact that there is copper and aluminum that expand and contract at different rates. Contaminants or moisture have nothing to do with this type failure.

The second cause of evap failure is moisture in the system due to poor service. Poor service would mean a lack of drier replacement when the system is open and/or improper or inadequate evacuation. The moisture combines with the refrigerant to form an acid that will eat up the system from the inside out.

Soooo... If the system is leak free and has been properly evacuated you will NOT have moisture in the system, but opening it up for "preventive" evacuation and recharge introduces the possibility of moisture introduction and contamination.

That said, if the system was NOT properly evacuated, then it should indeed have the charge recovered, filter/drier replaced and PROPERLY evacuated and charged.

This is the epitome of "if it ain't broke don't fix it!"

Have a great day,

A corallary to that saying is ......
"If It Ain't Broke, It Hasn't Been Fixed Enough"

Sometimes, performing maintenance on something that does not require it only introduces problems. As stated, this is definitely the case here.

LarryBible - thanks for your input. I'm sure I'll know what your opinion is when it comes to AC "stop leak" type products. I did hook up with an AC technician who does use these products from time to time with good results. I told him of all opinions/stories I've heard about why this is a bad idea and that these products can actually damage the AC charging equipment. He told me he's had no such problem and that he wouldn't use them if it would wreck his machinery. He seems very sincere/trustworthy. He was the only AC shop that suggested testing my system with both a sniffer and UV lamp (after recharging with dye and driving around for a week).

tkd_M119:

If the tech who uses "stop leak" is the same tech who told you to vacuum the a/c system as part of some sort of maint. regimen, I would find another tech.

Use the search facility here. You'll find more than one negative post regarding a/c "stop leak" products from people here who do this for a living.

a/c "stop leak" products are nothing more than snake oil. Not only will they damage a/c service equipment, but eventually, this stuff will deep-6 your a/c system.

Back to my original thread. . . . I spoke with a service rep. at a NoVA Mercedes dealer's service shop, and he said that the "fix" for the W140's evaporator problems made the a/c system "better" than the original design. He said that in all of his years, he has never seen a W140 come in for a 2nd evaporator replacement service.

FYI.