124 AC. Possible short?
 

I am sure the answer is in this forum somewhere but either I missed it or I am using the wrong key words to search.

My wife's 1995 E300 D is having an A/C problem. Seems when she drives through a puddle or goes through a car wash the AC stops blowing cold and blows hot. After the car dries out it all works normal. I am assuming it is an electrical short somewhere. Any suggestions on where to start looking and what to do when I find it?

Thanks

These cars have a sensor that detects belt slippage. If detected the compressor is switched off until the car is shut down and re-started. So could be that the belt tensioner is not set correctly, or it is wearing out.

The easy way is to stop by a MB shop and have them adjust and/or check the adjustment.

Steve

Water is splashing up onto the clutch for the A/C compressor and its slipping - as Steve says when the system detects the belt slipping it cuts out the compressor until the next restart cycle.

You could have can excessive gap on the clutch contact plate. Are the underbody noise panels installed on the car? Unless she is driving through puddles that are 8-10 inches deep I'd expect the panels to keep the water off the A/C compressor clutch.

Steve is right on that, I bet.

Your wife must go through some big puddles!

The belt is probably getting wet and slipping.

the first time this happened to me, I freaked.... it only happened one time.

she must be hitting some puddles pretty hard.

Let us know about the under belly cover. This is a rather large plastic pan that literally covers the underside from the bottom of the radiator to the back of the engine. Seems like it must be missing, otherwise, how could the carwash get to the A/C clutch. Spray must be coming up from underneath, as the hood closes down on rubber seals to keep water out of the engine compartment.

Steve

The belly pan is on (at least it was 2 days when I changed the oil). I washed (by hand) the car that same day and when I went to pick my wife up I had the same problem. I think I remember shutting down the engine and restarting thinking it was a cycle problem like indicated above. I have a 16v that had the belt problem. I stopped to get fuel and still had no AC. Drove to the airport and parked for an hour or so and on the drive home we had AC. That is why I thinking electric.

I do hear a chipring sound on cold start up and idle like a slipping belt so I guess that will be a cheap theory to test.

At a certain point MB changed the belt tensioner design. I suspect you have the older style which is adjustable. Do a search on 300E Belt Tension. There are some good descriptions available. Should tell you how to adjust the tension. If the tensioner has never been replaced, then it is probably just worn out and needs to be replaced. Be aware that adjusting a tensioner that is toast can result in not being able to get back to the tension level you had before trying to adjust, i.e. you are done until you replace it. Happened to me twice on two different 300E's.

Steve

Ignore what I said about belt tensioner, different on a diesel. Missed the diesel fact.

Steve

If you have a set of feeler guages (as for valve adjustments) check the clutch gap on the compressor. The spec is 0.50mm, plus or minus 0.15mm. In my limited experience, once the gap reaches 0.80-0.90mm the engagement becomes flaky. Excess gap is particularly suspect if it works fine when the car is started cold, but then stops after a period of time.

Grease/oil on the clutch surfaces can cause enough slip to trigger the cutout. An easy/cheap fix is to degrease it. Use anything from brake cleaner to simple grean. Just soak the area of the clutch gap, wait, rinse with water if necessary. Some folks have had this treatment cure their ills.

- JimY

Update.

I d not have any feelers but I took a look and the clutch plate seem to very close to the main unit. I am guessing 3 pieces of paper, maybe only 2.

I did notice that there is a hole in the inner fender well about 5 inches or so from the dryer. The hole is about 2 inches in diameter and has a twin on the other fender. That one has what looks like a rubber drain plug on it, the one by the dryer does not. I can see the tire through the hole. Could water have come through the hole and shorted out some of the connections at the dryer? There is a bit of oil/dirt on the compressor. I’ll try and clean that out next weekend when I have more time.

Any other ideas?

Thanks

Sure seems like you found the problem. Go to the dealer and order the rubber plug.

Steve