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  #1  
Old 05-11-2016, 12:13 PM
BamaMB's Avatar
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Location: Birmingham AL
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W140 A/C compressor turning but no pressure

Last three years each summer I have had to add a small amount of freon to get the A/C to blow cold and it would last all summer. I just attempted to add some freon, the compressor is turning, clutch engaged but it is not building any pressure. I have gauges and the hi side equals the low side. Beside the obvious, failed compressor, is there anything else I should check before I get a new compressor?

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2001 E320 wagon
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  #2  
Old 05-11-2016, 07:53 PM
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If clutch engages and is visually seen as turning and there is no pressure difference between high and low sides (the ratio would likely be 6-7 or so), then it must be the compressor. To confirm that the clutch is totally engaged, you could energize the clutch directly from the battery.
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  #3  
Old 05-12-2016, 08:14 AM
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I have the same problem,I put sealer in mine,as they leak in the car.My controller inside has buttons that don't work,so I can't reset the code.I need to buy keys to pull unit out,and carefully glue buttons back on.I saw where one guy used rubber parts to repair where tabs touch buttons.
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  #4  
Old 05-12-2016, 10:49 AM
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If you have a late model W140 it would be having the variable stroke compressor like used in the W210, W202, W163 and even on some GM products. This compressor has a unit that adjusts the pressure between the low and high side to keep at lowest load level and optimum performance depending on the refrigerant pressure its seeing.

If the system gets flooded with oil or if you accidentaly put sealant in there the variable unit stops working and the compressor basically bypasses everythign as it considers there is no refrigerant in the unit.

There is also another catch, the early model compressors have a failure point, its reed valves break internally and cause the same symptom, this was updated by Denso (maker of the system) later on.

The partial good news is that you can get this compressor from a laundry list of benz models and even some BMWs from a scrapyard Or you can get a new one (of chinese origin) for about 200 and then redo the system. A benz boxed part is about 500, an OES part would be between 250-300.
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  #5  
Old 05-12-2016, 12:22 PM
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I have a 99 S320 and have never put any sealant in the system, just 1/2 can of 134 when needed. With the engine off and clutch disengaged, I can turn the compressor shaft and it has no resistance. Is there a shear key or pin in the clutch in the event of a frozen compressor shaft?
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  #6  
Old 05-12-2016, 03:48 PM
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Quote:
Originally Posted by BamaMB View Post
I have a 99 S320 and have never put any sealant in the system, just 1/2 can of 134 when needed. With the engine off and clutch disengaged, I can turn the compressor shaft and it has no resistance. Is there a shear key or pin in the clutch in the event of a frozen compressor shaft?
the volume metering device in the compressor has failed, or the valve plate has broken and the compressor is just bypassing.

In both cases you need a replacement compressor as the variable device is not easily available and if its the original factory compressor install then better buy the updated one to prevent this.
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1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
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  #7  
Old 05-12-2016, 05:11 PM
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Thanks for the help. I figured that the compressor is shot, just wanted to make sure there wasn't any other likely issue or failure.

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