The Plus4 can sometimes suffer from Heat Creep in certain conditions. This duct/plenum attempts to better route the air from the intake fan over the heatsink to minimise the risk of heat creep for parts with many fine retractions, or at certain filament temperatures.

By default, there's about a 10mm gap between the outlet of the fan, and the surface of the heatsink, and there's many paths of lesser resistance for the air to flow, instead of through the heatsink. This design is intended to be a snap-in-place piece that minimises the air-flow loss and better cools the heatsink.

Installation

First unplug the hotend cable plug from the print head board, and release from the sliding clamp that holds the cables in place (ie. about mid-way along the cable length)

Now, very gently, move the cables out of the way, and install the duct as per the photographs. Push the duct in place until it seats firmly against the extruder. It may help to hold the fan cable to the side (left) of the long tip of the duct such that it is not bending the fan cable excessively.

Now slide the hot end cables back onto the clamp, and re-plug back into the print head board.