Or did they on some models???? Just curious....

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Are you referring to the AC system?

Orifice tube systems are pretty coarse control compared to expansion valve systems and likely why Mercedes didn't use it.

GM developed the CCOT ( Clutch Cycling Orifice Tube ) strategy of AC control along with the R4 compressor in the mid 70's. It offered a cost reduction over the prior VIR ( Valve in Receiver ) and A6 compressor.

CCOT uses a pressure switch on the low side and a orifice at the entrance of the evaporator. As the compressor runs, it pumps the freon into the condenser but only so much can flow through he orifice tube, as the freon backs up the low side pressure drops. Once the low pressure drops the compressor shuts off, system continues to bleed off, low pressure rises and compressor turns back on.

The system is pretty coarse compared to a ( TXV ) Thermal Expansion Valve . A TXV looks at gas temp exiting the evaporator and varies the flow into the evaporator as needed. There is also a low pressure switch on the low side to shut the compressor off in case the system is run on a cold day and the TXV is staying closed.

I have worked on a lot of A/C systems, and although 'course' as you say, I can tune a CCOT system so much easier than I can a TXV system...

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership