CLK320 Strange Air Conditioning Problem
 

2001 CLK320 107000 miles

When the air is turned on, it blows cold air for a few minutes, then the compressor shuts off and it blows ambient air.

I took it to my technician who suspected the system was low on Freon. He evacuated the system and re-charged it. The symptoms didn't change at all. He checked for error codes in the computer - there were none. He said to go back in a week, and if no errors show up, there is 90% likelihood that the compressor clutch is defective.

1. The clutch works fine when it gets juice. Could it still cause this problem?

2. Could the problem be caused by the pressure switch (on the receiver drier) that is not sensing the pressure in the system and is shutting off the compressor?

3. There is second sensor on the receiver drier. What does it do?


Thanks

1. clutch sounds like its okay, something is cutting power to the clutch

I know some of the newer systems like yours have a sensor somewhere which will cut off the compressor if it detects that the compressor is slipping on the belt. Could be a possibility.

It could also be shutting down due to incorrect system pressures, cause by to much or to little freon, a expansion valve that is acting up, fans on condenser not running causing pressures to go up...

You need to put gauges on the system and monitor pressure until the system starts to show problems like you are explaining.

I am assuming the "EC" light comes on when it quits?

I will check on the EC light this evening and post back.

Responding to '79Mercy', the belt is not loose. The tech who replaced the Freon said the amount evacuated was about half of what it should have been, but even then it was blowing freezing cold.

If I unplug the harness from the pressure switch to check for continuity, will it throw an error code?

Thanks

I believe it'll throw a code, yes.
What I was going to mention, and you might have to research this a bit, should be info online:
There was originally a sensor in the system, trying to remember what it monitors, moisture in the freon possibly? Ach, all getting a bit foggy now. But anyways, there was a bulletin out about going in to the AC control system and disabling this monitor as they were acting up and turning off the AC system.
If this were ther case, a tech with an MB shop computer would access the controller and disable the monitoring of......again foggy on what it was, but it could be changed so the system didn't monitor for it any more.
The EC light being on would be "normal" in that if the AC clutch is being commanded off, the EC light should come on, irregardless of the reason. And it seems to me that 2000-2001 was about when this was taking place, especilaly in the 210s and I think the 208 as well. Saw a lot of 210s with this.
Another common problem is one of the temp sensors going bad, in your case I'd suspect possibly the evap temp sensor reading might be found to be implausible.

OK, I found online what I was (sort of) looking for.
The monitoring that is taking place is actually for freon LEVEL or quantity. On some models, this has to be set to "inactive" due to a software problem, again IIRC this was right arounf MY 2000-2001, I am thinking if no other faults can be found that this might do it. I'd be sure to check the actual values of the different temp sensors first.
Here is a link to what I stumbled on:
http://forums.mercedesclub.org.uk/showpost.php?p=247445&postcount=9
Beware though, this post makes it sound like monitoring of the PRESSURES is not taking place and you are screwed if the system loses pressure, which is NOT the cas,e the compressor will still shut off if it needs to. This "quantity" measuring thing I don't think ever really served a real purpose than to cause techs headaches.

The most common problem is the evaporator temp sensor! 210-830-07-72

At any time you can see actual values thru the a/c pushbutton, either try searching here for that procedure OR send me a e-mail & I will get you that info.

Is that in about the same position as the 210 chassis? Kind of above the throttle?