Volvo's ECC system controls air distribution via vacuum. When the engine is loaded (acceleration), intake manifold vacuum drops. If the system has a leak, vacuum is insufficient to hold the flap in position, and spring force returns the air to the default position, which is usually the footwell.

Dual-function vacuum bell: Located inside/on the side of the heater housing. The membrane ruptures over time. Heater control valve: A valve in the engine bay can leak vacuum or its hose may have worn through. Check valve: A small valve near the engine fan, whose purpose is to prevent vacuum from escaping into the intake manifold during load.

Bell replacement is a labor-intensive operation requiring disassembly of the center console and lower dashboard sections. Disassembly Steps: Footwells: Remove protective covers on both sides. Center console: Remove the handbrake trim and storage pockets. Dashboard: Remove the stereo, glove compartment (to access the side panel), and fuse cover. Side panels: Remove both side panels (fastened with bolts near the seat, interior edge, and upholstery). Electrics: Remove the relay/fuse box from its mounts (2 bolts, 1 nut) to make room.

Once you've disassembled the air ducts and small air box (fastened with one Torx), the vacuum bell is revealed. The bell is fastened with two 10 mm bolts on the inside. Disconnect old vacuum hoses and mark their positions. Install new bell and ensure its rod engages correctly with the air flap mechanism.

If obtaining a new original part is difficult (delivery times can be long), some enthusiasts have successfully patched a torn membrane with flexible adhesive or rubber coating, but this is usually only a temporary solution. Another option is to find an intact bell from a junkyard car, but they are often equally fragile.

You can test the system by "puffing": disconnect the vacuum hose from the engine side (which goes into the cabin) and use a manual pump to suck or blow into it. If pressure doesn't hold, there's a leak in the system. Usually a hissing sound can be heard clearly from inside the dashboard when using a manual vacuum pump.