Ports 1 and 2 operate the recirculate flap on the vacuum switchover solenoid block. One of them is the "short stroke", the other is the "long stroke". I don't remember which is which. The solenoid block is known for having bad/broken solder joints internally. You have to cut the back off to get in there to resolder it or buy a new one. Use a Mightyvac to test the lines connected to 1 and 2 and see if they hold vacuum. If they do, you know the issue is probably in the solenoid block. If they don't, it's a bad fitting somewhere, broken vacuum line, or a leaking vacuum pod.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]