Because of the evaporator temp regulator preventing evaporator freeze-up. Not the same as a cycling system.

If it does not turn off the compressor.. how does it control it....to keep the evaporator from getting below 32 degrees.. thus freezing moisture content of the ambient air... on the outside of the evaporator.... causing the air to not be able to flow past the fins...
when it showed a TxValve..which is typically a combo block valve in our cars...
I assumed a cycling system ...
A non cycling system usually has an orifice instead of Txvalve....and an accumulator instead of reciver/dryer...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html