The lower line is a "manifold" line that connects to the compressor and is connected to the low pressure line.

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=2D11A53C82D719FUFA&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1985&product=R1020-11584&application=000037515

First it is expensive. Make sure the hydraulic shop can do the job. If they can't I recommend a OEM hose not the after market ones. The quality is not to good on the after market hoses.

All lines on the AC system are SAE not mertric.

Get the large Harbor Freight open end wrench set.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=39488

Second. Are you 609 Certified? If not then opening the system is not allowed. I would suggest you get 609 certified. Going through the program will teach you what you need to know to work on your system. It's not hard.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car