240 DA Air Conditioning retrofit

[Sorrento 25]

In your vintage 240 there is no provision built into the boat to isolate the A/C unit from the hull liner. For a proper installation an isolation divider needs to be constructed and installed to prevent air from the hull liner from being pulled into the return air for the A/C unit. If this is not done you will have a very stinky cabin on your hands.

This is not clear to me. Isn't there a dedicated return duct anyway? What do you mean by "hull liner?"