Why does your air conditioning quit in your 1991 190e Mercedes Benz?

Answer 1

This is taken from my MB page at www.cacavas.com. There are several reasons why a compressor might not turn on. To test, select the top button (max AC) and then the button with the two boxes on it, meaning the center and side vents. The system must pass several internal tests before the compressor comes on. Recently my compressor stopped working, but I noticed that it coincided with the failure of my tachometer. One of the internal tests is that the compressor must be spinning at the same rate as the engine. If anything prevents this, then no cold. This includes oil on the belt, or belt slippage of any kind, or in my case, a faulty engine RPM sensor. The system was told that the engine is not spinning, but the compressor is, and it failed the test. If you have a diesel and your tachometer is not working, take a look at the RPM sensor. It is mounted on the engine bell housing, on the same side as the oil level sensor, just a bit farther back. You can get to it by removing the front lower panel, as you would do when changing your oil. Look a bit farther back than the oil pan, on the bell housing, and it is a little black thing with a wire on it which points straight up. In my case, the wire was broken, and I was able to take it out, cut away about a quarter inch of the black plastic housing, and then solder some new leads onto the wire stubs. I taped it up and now the tach works fine, and once again the air conditioner works as it should. If yours is bad and you can't fix it, they can be had for about sixty dollars. The other end of the wire terminates in a small connector located behind the battery, under the leaf trap. Sometimes the KLIMA relay (N6) can go bad. I've never had this happen, but be aware that it can. It controls the air conditioner function. Pull out the relay, and jumper pins 5 and 7. If your compressor has gas, then it should quickly cool down your car. If the evaporator temperature sensor opens, then the air conditioner will not kick on either. If the clutch slips on the compressor, due to either dirt or a bad electrical connection, then the compressor will shut off. If your car has an overload relay, and the fuse is bad or the contacts are dirty, it may not function properly. If you find that the gas has leaked out of your system, and you need a recharge, ask the shop to recharge the system and add their special yellow/green dye. Then run the car with the A/C on for a few minutes, and then have them take a look under the car with their black light. If there is a leak, it will show up in a very obvious way. My recent leaks have been on the back side of the compressor, and there are three o-rings which can cause the leak: two are on the hose manifold, and there is a third under the snap ring on the very center. I believe this is the speed sensor. The compressor comes out easily. The shop may be tempted to do only the two most visible ones, but insist they do the third as well. You don't want to have to pull the compressor any more than you have to. You may also have bad hoses on the manifold. You can either buy a whole new manifold with hoses, or have new hoses put onto your old manifold. I cover my hoses with plastic tubing to keep oil from dripping on them and ruining them prematurely. If your compressor comes on but makes a huge amount of noise, or locks up, it is most likely shot. John Cacavas jcacavas@gmail.com www.cacavas.com