Hi everyone. Does anyone know what this hose is? (image taken from Haynes 123 manual)

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1984 300TD Turbo 156Kmi
"He who seeks knowledge begins with humbleness" - Buju Banton

As far as I know its the Low pressure Pipe from AC compressor. This is th pipe on which you have the AC charging port. Its right in the front slightly to the left. And like Bill said its the foam cover on it that makes it look like a hose. You can trace that pipe down to the compressor. Hayes has shown same pipe but only a section of it.
Hope this helps.
MVK
I can send you e-mail of a nice picture that will clarify further, if you want.

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles

Thanks for the info. On my car, some of the foam insulation started crumbling, so I thought I'd order a new one. The Haynes never labeled it or mentioned it. (At least the Haynes was good for a photo.)

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1984 300TD Turbo 156Kmi
"He who seeks knowledge begins with humbleness" - Buju Banton

You can pick some up from home depot. Buy a slightly oversize diameter. Split it along the length and then slide it over the pipe. Make sure you remove the old one or you might have the sponge crums all over in your engine compartment.
Once you slide it over the pipe, wrap it nicely( That the reason for slighlty larger diameter) and use wide width plastic ties( like the yellow ones you get with the garbage bags)and hold it in place.
Thats it. Thsi way you avoid taking out the whole pipe fitting. And you thats an expensive affair.
MVK

__________________
One penny saved is three penny earned.

1985 300D Turbo 179,000miles