I've got similar problems with the Klima on the SDL. I traced it down to the compressor speed sensor. The sensor should provide a reading of .3V at idle. It provides less than .2V. It should have a resistance of 550 to 650 ohms. It has 1000 ohms.

It appears that this speed sensor is on the back of the compressor on the shaft centerline.

There is some mention made of an air gap. But, I'm thinking that it's not applicable to this unit?

Can anyone, maybe Arthur, comment on how the speed sensor would be setup on this compressor and how to remove it??


Edited:

After making up the bypass ice cube relay and installing it, the problem is identical:

The compressor runs for about four minutes and shuts down. No change in symptoms.

So, the low pressure switch is ruled out, the Klima is ruled out. What else can possibly shut the compressor down and leave it shut down?

I started another thread on it. I'm at a loss.

300 SDL A/C electronic controls

Brain,

I had a similar problem. Compressor sensor resistance was not correct. Replaced the 3 wire connector on the compressor, AC works fine!

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Zafar
94 E320 58000 Miles

Yes, I thought that was the case with this one, as well. But, removing the Klima from the system and running it with the ice cube relay confirmed the problem remained. So, the sensor on the compressor was doing the proper job.

If you bridge pins 5 & 7 on the Compressor Relay Socket, does the compressor continue to run?

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Zafar
94 E320 58000 Miles

Yes, it did.

Looks like you have already ran the 6-7 tests for the Compressor Clutch Relay.

You may want to run the AC Control Unit Diagnostics. alldatadiy lists all the tests.

The compressor engagement on my car was intermitent. Then it would engage at startup but disengage shortly. Bridging pins 5 & 7, the compressor stayed engaged. Repalced the Compressor relay. Did not fix the problem. Took it to the MB dealer, that is another story! I have yet to find a satisfactory MB dealer. End result, I was overcharged and problem not fixed. I declined the $675 speed sensor repair. For that price, one can get a new compressor!

Ran my own checks, all 6 of them for the compressor relay. Ordered the ICe Cube Relay from ebay. Meanwhile, found power connector at compressor loose. Replaced connector, around $5. Everything working fine. Temperature at the vent 38F.

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Zafar
94 E320 58000 Miles

Bridging pins 5 and 7 eliminate the Klima and the PBU from the system. So, you really don't know anything, at that point, other than the compressor clutch works properly. The problem can then be any of the signals to the Klima, the Klima itself, the PBU, or any of the signals to the PBU.

In my case, using pin #10, the ground from the PBU, the problem remained. So, this now effectively rules out the Klima and all inputs to the Klima.

A second PBU eliminated the problem, however, it's more likely that the evap temp sensor is out of limits (2.2K resistance) and causing a default in one of the PBU's. They are not exactly identical........one of them is a newer version and must have slightly different internal circuitry.

I hear you regarding the dealers. You take the vehicle there thinking that they have better knowledge and troubleshooting skills than you do. In reality, you get a parts changer with his head up his ass.