A solution to the prevention of w124 evaporator issues

[POS]

I'm 37, and I've known my MB mechanic Hans since the late 70s when my father drove a 280SL Pagoda and 280SE 3.5. Since the 70s, he only worked on MBs, and he's seen and fixed them all. For thirty years this excellent man has been my family's mechanic, and I completely trust what he says.

His advice for preventing evaporator issues: (1) Keep the pine needles and crap out of the vents in front of the windsheild, and (2) replace the R12/R134 once a year. When moisture and air get into the system, the evaporator corrodes, so vacuum out all the air and put in new freon once a year and the evaporator will go on forever.

I thought it might help some of you with really cherry w124s to keep them cherry.

[brewtoo]

That could work.

I don't know if it would be effective against the aluminum-eating mites that Mercedes-Benz blames this on, though. They go from the outside in.

[OldPokey]

Or road salt.

[david s poole]

when a refrigeration system is working properly[correct pressures and temps]there is no air or moisture in it.so how do the above recomendations help anyone except the tech doing the work and selling the refrigerants.sort of like telling your customers that changing oil every 500 miles will improve your gas mileage and keep the car running an extra 100,000 miles.

[atikovi]

replace the R12/R134 once a year. When moisture and air get into the system, the evaporator corrodes

The a/c system is always under pressure so additional moisture and air can't get into the system unless it's been completly discharged.

[dpetryk]

I don't buy it.

Originally Posted by POS

I'm 37, and I've known my MB mechanic Hans since the late 70s when my father drove a 280SL Pagoda and 280SE 3.5. Since the 70s, he only worked on MBs, and he's seen and fixed them all. For thirty years this excellent man has been my family's mechanic, and I completely trust what he says.

His advice for preventing evaporator issues: (1) Keep the pine needles and crap out of the vents in front of the windsheild, and (2) replace the R12/R134 once a year. When moisture and air get into the system, the evaporator corrodes, so vacuum out all the air and put in new freon once a year and the evaporator will go on forever.

I thought it might help some of you with really cherry w124s to keep them cherry.

Your technician sounds like a great guy and an experienced, savvy tech, but I TOTALLY disagree with him on this one.

I will go along with his advice for keeping the cowl vent clean, but the rest of it WILL not work to prevent the 124 evaporator failure issue and if carried out incorrectly could cause other problems.

To begin with, the 124 evaporator problem has LITTLE to do with corrosion. The problem is that the evaporator is bimetallic. That is, the coils and ends are of two different metals with two different expansion/contraction rates. This is where the designers made the big goof. After a certain number of heat cycles of differing expansion/contraction a tube will sometimes pull loose. Unlike some folks believe, these evaporators are NOT destined to failure. My 88 300E still has the factory evaporator and it is still as tight as a drum.

With any automotive item a failure rate of 10% is astronomical, and can make it appear that ALL components on ALL cars like it, will fail, but it is perception, not reality. I have no idea what the failure rate is on this component, but it falls way short of 100%.

Additionally, Hans is correct that moisture combined with refrigerant makes acid, but changing the refrigerant once a year is the WRONG way to prevent this. In fact, it could exacerbate the problem if it does not get a THOROUGH evacuation when the refrigerant is changed. If there IS a leak in the system, there is pressure in the system, so moisture will not get in unless the charge leaks out to a point that there is a vacuum being pulled on the low side and the leak is on the low side.

Personally I believe Hans is trying to promote some easy, annual business from his customers. I also believe that to do the best you can to care for your 124, or any auto a/c, keep everything clean and watch for lower a/c performance. If it does fall off, put on the guages and check the charge. If there is a significant leak that requires chargin annually or more often, then find the leak, wherever it is, fix the leak, change the r/d, PROPERLY evacuate and recharge.

You DO NOT change refrigerant like you change oil.

My $0.02,

[brewtoo]

Originally Posted by LarryBible

With any automotive item a failure rate of 10% is astronomical, and can make it appear that ALL components on ALL cars like it, will fail, but it is perception, not reality. I have no idea what the failure rate is on this component, but it falls way short of 100%.

I bet it approaches or exceeds 50%, at least here in the southeast. I have a number of friends with these cars. ALL have had to replace the evaporator, with the only exceptions being my 1991 W124 and a friend's 1995 W124 (so far).

Originally Posted by brewtoo

I bet it approaches or exceeds 50%, at least here in the southeast. I have a number of friends with these cars. ALL have had to replace the evaporator, with the only exceptions being my 1991 W124 and a friend's 1995 W124 (so far).

Yes you would expect more failures in the South because the heat cycles would be more drastic due to the harder work that the system must perform. My point was that it is not 100%. I do believe that it is very high, but when people consider it inevitable, they get themselves in a tizzy and possibly even crack open the system unnecessarily.

[langpfeife]

Originally Posted by LarryBible

Your technician sounds like a great guy and an experienced, savvy tech, but I TOTALLY disagree with him on this one.

I will go along with his advice for keeping the cowl vent clean, but the rest of it WILL not work to prevent the 124 evaporator failure issue and if carried out incorrectly could cause other problems.

To begin with, the 124 evaporator problem has LITTLE to do with corrosion. The problem is that the evaporator is bimetallic. That is, the coils and ends are of two different metals with two different expansion/contraction rates. This is where the designers made the big goof. After a certain number of heat cycles of differing expansion/contraction a tube will sometimes pull loose. Unlike some folks believe, these evaporators are NOT destined to failure. My 88 300E still has the factory evaporator and it is still as tight as a drum.

With any automotive item a failure rate of 10% is astronomical, and can make it appear that ALL components on ALL cars like it, will fail, but it is perception, not reality. I have no idea what the failure rate is on this component, but it falls way short of 100%.

Additionally, Hans is correct that moisture combined with refrigerant makes acid, but changing the refrigerant once a year is the WRONG way to prevent this. In fact, it could exacerbate the problem if it does not get a THOROUGH evacuation when the refrigerant is changed. If there IS a leak in the system, there is pressure in the system, so moisture will not get in unless the charge leaks out to a point that there is a vacuum being pulled on the low side and the leak is on the low side.

Personally I believe Hans is trying to promote some easy, annual business from his customers. I also believe that to do the best you can to care for your 124, or any auto a/c, keep everything clean and watch for lower a/c performance. If it does fall off, put on the guages and check the charge. If there is a significant leak that requires chargin annually or more often, then find the leak, wherever it is, fix the leak, change the r/d, PROPERLY evacuate and recharge.

You DO NOT change refrigerant like you change oil.

My $0.02,

Larry I have to agree. Interestingly enough, here in the dry desert (Nevada) I have yet to see ONE W124 with a leaking or severely corroded evaporator. In fact, I didn't even reaslise it was a relatively common issue until I saw this thread, LOL.


cheers

[brewtoo]

Originally Posted by langpfeife

Larry I have to agree. Interestingly enough, here in the dry desert (Nevada) I have yet to see ONE W124 with a leaking or severely corroded evaporator. In fact, I didn't even reaslise it was a relatively common issue until I saw this thread, LOL.


cheers

If the problem is one of thermal cycles causing problems because of the different expansion rates of the two metals, wouldn't you also have the problem in a dry climate? Maybe not since the AC does not have to work nearly as hard as in a humid climate.

When I removed my evaporator, I did not see any significant corrosion BTW. I live in the southeast and my car was up north the first seven years of its life. It was not clear to me why or exactly where it leaked, but it was a nasty oily mess.

[just-n-time]

The use of the dryer is to handle that tea spoon of moister,If you need to be even more sure of a dry system,Use a commercial dryer set up with shut off valves so you can change the dryer every year,and only lose a small amount of freon,The use of R12 is in my opinion, not any better than freez12,so why waist the money?

Originally Posted by just-n-time

The use of the dryer is to handle that tea spoon of moister,If you need to be even more sure of a dry system,Use a commercial dryer set up with shut off valves so you can change the dryer every year,and only lose a small amount of freon,The use of R12 is in my opinion, not any better than freez12,so why waist the money?

Freeze 12 WILL cool as well as R12, but the disadvantage is as psfred pointed out. ALL junk refrigerants fall into one or both of the following categories; blend or flammable. The disadvantages to a flammable are obvious and the disadvantage of a blend is as psfred pointed out.

If you have an R12 system use R12. If you have an R134a system, use R134a.

There are numerous downsides to using anything other than the above two refrigerants. To begin with, it is ILLEGAL to use one of the junk refrigerants without using the proper fittings for that refrigerant. There are ZILLIONS of systems with junk refrigerants and the wrong fittings. This causes those who are recovering refrigerants to easily contaminate an entire cylinder of recovered refrigerant. When contaminated, they are supposed to pay to have it destroyed.

For this reason, most shops have a refrigerant identifier and will check a system before servicing. If it has anything other than R12 or R134a, they will not service it. They are caught in a bad situation. They don't want to contaminate recovered refrigerant and they can go to jail for venting it.

Stay away from the junk refrigerants and you will be doing EVERYONE a favor, most of all yourself.

[POS]

Excellent response, Larry. Thanks. Since I own an auto parts store and have simple access to vacuums, gauge sets, and refrigerants, I don't think he was trying to sell me more refrigerant - now certainly he might be to his other customers and he just told me his normal sales pitch. I liked his idea because it made a lot of sense to me, but after reading your explanation, you sound much more correct. One of the things I chalked down as a big caveat was that if you screw up the yearly recharge, you might be letting moisture into the system inadvertently.

[hitwtom]

David and Larry, both excellent responses, as a licensed refrigeration tech there is no reason to chance the refrigerant. I do however still have a bottle of R-12 if anyone would like their system recharged has anyone priced R-12 lately?