95 300D Air Conditioning Quit
 

I just had my 1995 300D into the shop for new V belt and they
replaced all the belt tensioner parts. Last weekend while I came
to a stop lite I heard some screetching of the belt. Subsequently,
the air conditioner became intermittent. Now it always blows warm
air and the belt vibration that was supposed to be fixed by replacing
the belt tensioner is back. Any ideas?

Brian

Best guess:
 

The compressor locked up.

Compress Lockup?
 

It seems to be intermittent. Some mornings it works and others it doesn't. New compressor needed or might there be some other possibility. If it does need a new compressor, is there a recommended Internet site to purchase one?

Brian

the problem might be related to the belt itself , in my 87 300d if theres slippage then the compressor cut off relay will cut out the compressor if the difference between eng speed and compressor speed is more than 30% for a certain amount of time (in seconds, dont remember how long) yours is probably the same or similar, this is done to protect the eng in case the compressor locks up. You mentioned the problem is intermitent so I dont think the comp is locked up otherwise you'll see the alt light come on the dash and lose power steering since that belt will definitely self destruct or jump the pulley if the compressor did lock up

mbonly is probably right on this. This is a subject that has been written about ALOT here on mshop. A search will give you more reading than you will have time to cover.

Good luck,

Have someone start the engine while you look at the AC compressor. If it turns on for 1 second or so and than immediately turns off than its most definitely shutting off because the speed sensor in the AC detected a mismatch between the speed of the AC compressor and the speed of the engine. The AC compressor will than not start again, unless you turn your engine off and on. The same cycle will likely than be repeated.

This, as other have said is most likely due to a slipping belt. Fix the belt and you should be OK.

Phil

Let's meet tonight..
 

I will be in Ann Arbor this evening to visit family. :)
You have PM.. :)

300D Compressor Intermittent
 

The saga continues. I took the 300D to both a local garage and
the dealership over the last couple of weeks. The local garage
looked at all the pressures (were fine) and suggested that the
dealership should see it because they could pull the codes and
be able to find the cause sooner.

I had the car at the dealership all day and the technician never
saw the compressor (clutch) shut off by itself. I went to pick
up the car, turned it on, and the compressor stayed off. I went
and got the technician who looked and looked and eventually
said it might be the RPM sensor on the compressor. He would
tear down the compressor and for $500 to $1000 would fix it.

I'm not so sure he's correct. The compressor does come on again
when you are driving. I noticed that when I was driving home.
All of sudden it got cool again. So.. I don't think it is the RPM
sensor because I didn't have to restart to reset the compressor.

One suggestion was the Klima module was faulty. I've been trying
to locate it in my 1995 300D. It isn't behind the battery. The
battery in my car is right up against the firewall. My sedan type
is 124.131 and the engine is a 606.910 (3L).

There's got to be a better way to diagnose the problem than
replacing a bunch of parts until you find it.

Brian

Brian,

I have the same car, and the KILMA relay is indeed located behind the Battery. Its behind the black plastic cover at the back of the battery. There are several other relays there as well.

You are right, the Mercedes manual does say that the AC compressor will not restart (after it has shut down because it sensed an RPM variance), until the engine is turned off and on again, BUT, it will restart on its own if the shutdown was caused by faulty wiring to the speed sensor. This can occur if the speed sensor wires are intermittently shorting, opening or grounding. In that case, the AC compressor will come back on as soon as the intermittent wiring fault fixes itself. Basically what I am saying is that the system seems to be capable of distinguishing between an RPM variance and a wiring malfunction. In the case of an RPM variance the compressor will not restart until you shut down the engine and restart it. In the case of a wiring fault the compressor will restart as soon as the wiring fault is removed.

I know this for a fact, as I had intermittent defective wiring between the AC speed sensor and the KILMA switch. These two particular wires carry a digital signal, and one of the two speed sensor wires was intermittently grounding, causing the digital signal to be attenuated. (The infamous wiring harness problem) the compressor would then go off and come on intermittently. This, without shutting down the engine. I fixed the problem by running two new wires.

There are several other possibilities. One being defective wiring to the auxiliary fan. This will cause the AC compressor to intermittently shut off as well.

Phil

95 300D Air Conditioning Quit
 

Thanks for setting me straight on the location of the Klima module. It looked
like the firewall until I touched it and found it to be fiber instead of metal.
Yes I do see the relays now. I keep looking at the AllData documents but
they don't show any protective shrouds. I'm still not exactly sure which
module it is. There is a tall module and then 2 shorter ones behind it.

At lunch time today I drove it home and was amazed to see the air
conditioner work 100% all the way home and back again. The outside
air temperature was about 68F. A far cry from the 90+ temperatures
that we were getting the last couple of weeks while the a/c was
failing.

Does that information help? Could it be something other than the Klima?

Brian

95 300D Air Conditioning Quit
 

I've been driving it around for the last while hoping it
would just plain fail. It seems to be humidty related.
On dryer days it works pretty well. When it gets
humid it starts acting up.

Today it was a dryer day and it worked flawlessly
until I took it through a car wash. While water was
spraying under the car it went off. As soon as the
attendent finished wiping it down, it came back on
(engine was running all the time) and worked flawlessly
the rest of the day.