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  #1  
Old 05-08-2008, 04:00 PM
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triggering A/C compressor 1995 C280 W202

Does anyone know if the A/C compressor on a 1995 C280 (W202) is triggered 100% "on" via the proper voltage & polarity signal (like the W124's), or is it one of those "new" types of A/C compressors that use a modulated signal to vary it's pumping strength ?

Thanks,
:-) neil

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  #2  
Old 05-08-2008, 05:21 PM
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The a/c controller (pushbutton) sends 12V to the compressor directly & watches for compressor speed input.
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  #3  
Old 05-08-2008, 05:50 PM
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Quote:
Originally Posted by M.B.DOC View Post
The a/c controller (pushbutton) sends 12V to the compressor directly & watches for compressor speed input.
My understanding is that the A/C compressor sends out a passive speed signal and it is upto the climate-control brain to compare the A/C compressor speed signal against RPM, and if the delta is too great the climate-control brain will disengage the clutch.

Which also means, if you don't have "brain" watching, the A/C compressor will just keep on pumping.

Please confirm.

BTW: if my understanding is correct, does this also mean that the pump when "on " is always 100% and doesn't use the speed-signal to vary pumping ?

Thanks,
:-) neil
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  #4  
Old 05-08-2008, 08:46 PM
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Quote:
Originally Posted by ke6dcj View Post
My understanding is that the A/C compressor sends out a passive speed signal and it is upto the climate-control brain to compare the A/C compressor speed signal against RPM, and if the delta is too great the climate-control brain will disengage the clutch.

Which also means, if you don't have "brain" watching, the A/C compressor will just keep on pumping.
As long as your substitute for the "brain" continues to supply a +12 signal the compressor will stay engaged.

Quote:
Originally Posted by ke6dcj
BTW: if my understanding is correct, does this also mean that the pump when "on " is always 100% and doesn't use the speed-signal to vary pumping ?

Thanks,
:-) neil
The variable displacement A/C compressors that I've seen do not rely on electrical signals to modulate pump displacement. The compressors respond to pressure changes in the suction side of the system, low pressure (like 20-25 PSI) reduces displacement and higher pressures (like anything > 40 PSI) increases displacement. This is typically done via a swash plate with mechanical linkages.

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  #5  
Old 05-08-2008, 09:57 PM
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Quote:
Originally Posted by TimFreeh View Post

The variable displacement A/C compressors that I've seen do not rely on electrical signals to modulate pump displacement. The compressors respond to pressure changes in the suction side of the system, low pressure (like 20-25 PSI) reduces displacement and higher pressures (like anything > 40 PSI) increases displacement. This is typically done via a swash plate with mechanical linkages.

No electrons required.
Tim,
according to the linked article, starting in 2001 Denso started using "electrons" to change compressor displacement:

http://www.search-autoparts.com/searchautoparts/Teardown/ArticleStandard/Article/detail/156230

Since I'm looking at a 1995 compressor, the "old" mechanical method applies to me.

:-) neil
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