Heater Control Boxes & Ductwork

 

The Heater Control Boxes (993.572.786.00) hang below the engine and are held in place by their inlet and outlet red neoprene ducts. I know from personal experience that if one of the ducts slips off a box, the box can hang down, drag on the ground, and get ripped off or damaged.  A damaged or missing box may allow exhaust fumes to enter the cabin, and so it should be addressed as a safety issue.

For these reasons, the Heater Control Box ducts should be inspected at each oil change for rips or misalignment. If they seem to be hanging low, it indicates a problem.
Getting to the boxes is easily done by putting the rear of the car on jack stands, removing the rear tires, and reaching under the car through the wheel wells, one of the easier DIY projects.

A new Heater Control Box costs $1,000 from the Porsche dealer,

Heater Control Box

or between $250 and $500 used on eBay. The 72mm inner diameter (ID) straight duct material (000.043.205.04) is only sold by Porsche dealers in bulk lengths at several hundred dollars each, and then a section is cut to the required working length. It can also be purchased in precut lengths of 45mm or 80mm on eBay for $25 to $30. Unlike the original Neoprene duct, the Porsche service replacement duct is very soft, thin-wall silicone rubber without fiber reinforcement, resulting in reduced tear resistance compared to the original installed at assembly.

A better alternative to the dealer-supplied rubber duct:

Amazon offers a 70mm ID thick-wall silicone hose with fiber-reinforced ply, like the reinforced duct supplied at Porsche assembly. It is clearly more rip-resistant than the Porsche-supplied service duct. When measured, it came in at 72mm ID, the same ID specified in the Porsche parts catalog. It is a more durable alternative.

Amazon 70mm (72mm)
reinforced silicone hose

 

Also, the original duct clamps may be misshapen and fail to adjust, so it may be advisable to replace both clamps per hose. They are inexpensive “European Style” hose clamps on eBay or Amazon. The hose clamps sold at a hardware store have wider bands and may not work as a direct replacement for the duct clamps.

Cutting the duct to a serviceable length:

Although the factory specified cut lengths are 45mm or

 80mm; depending on the application location, one can consider adding some additional length. For example, the specification of a 45mm duct (call out "7" in the illustration at the top of this page) actually provides a better grip margin for the clamps if it is cut to 64mm, better keeping the boxes in position.

Dealer Supplied 72mm 
Non-Reinforced Thin-Wall Duct

Avoiding drama when installing the duct:

During assembly, I find it best to leave the clamps loose and hanging from the metal ducts, tucked out of the way, for both the front and rear connections to the boxes, giving one freedom of movement to get the rubber duct around the metal duct edge and position them in the best place for the clamps. Once you are satisfied that the rubber ducts are correctly positioned, the band clamps can be slipped into place and tightened. 

I ended up using the thicker-walled black silicone duct from Amazon,

Heater Control Box
in position with the black silicone duct.

cut to a 64mm length. The stiffer duct material does a good job of keeping the boxes tight and out of the way, even before the clamps are attached.

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