A solution to the prevention of w124 evaporator issues
 

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.

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.

Or road salt.

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.

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.

I don't buy it.

The evaporators more likely fail due to corrosion from the outside. They get wet and then the vehicle is parked and they don't get a chance to dry out. Benz also uses foam to seal around the edges of the evaporator. This is like a sponge that would take a long time to dry. Replacement evaporators from Benz (at least for the 124 bodies) use a hard plastic strip to seal around the edge which may help.
Probably a better way of extending the life would be to go to economy mode a few blocks before you park the vehicle for the night to help dry it out.
General Motors had a kit a few years back that you could wire in so that the blower would stay on for a while after the car was stopped. This was to help reduce the possibility of mold growth and the odors that resulted. As a bonus the evaporator life would probably be extended.

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,

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.

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.

I bought R12 year before last. It was $400 for 30 pounds which was down quite a bit. Since the vehicles requiring it are hitting the wrecking yards in record number now, the demand is rapidly declining, thus the price is continuing to fall.

The price is artificially inflating by $.50/lb a year due to taxes.

Last price I heard, if you can find it, was around $1200/bottle.:eek: