i don't know what that tube is you refer to.
the expansion valve on mine is just above the throttle petal, yes a pain to work up there but not impossible. i used a 22mm on the big nuts and a 19 on the others i think. used a cresent to hold the valve and slightly position it when needed.
i removed it to do the proper flush of the evaporator. lots of gunk came out.
i don't have everything back together yet, but just work a little everyday.
i can see up there that if you take the instrument cluster out you could reach the valve but, yeah, the air tube would be in the way.
good luck, i hope you get it cooling soon.
r

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1985 300SD
1998 Jetta TDI
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