'82 300 TD. When I bought this car a few years ago it had the pictured vacuum tube (green w/ yellow stripe) disconnected and the fitting attached to the green piece (check valve?) plugged by an RTV silicone cap. It's shameful that it's taken this long for me to try to work out what it does. I stuck the mighty vac on the green w/ yellow tube and it solidly holds vacuum. Maybe I'm being overly simplistic, but should it just be plugged into that check valve connection? What does that green/yellow tube actuate?

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Your climate control?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

^ I believe so.

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83 SD

84 CD