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,