Matt5112 supercharges our Volvo S80 turbocharger knowledge by answering a S80 Forum question on the TCV and related vacuum line routing — and in a larger scope — how turbocharging works on Volvo S80s. For those who benefit from photos, there are a bunch in this topic.
Blue/fresh air goes on the bottom of the tube right after the MAF on the fitting closest to the engine. There should be two more fittings there. Large one for the diverter valve/compressor bypass valve dumped air flow. Medium sized for the evap.
The Red/turbo pressure line goes to the two tubes that merge into one on the top centre of the engine.
The pressure from the outlet of the turbo presses on the wastegate diaphragm to keep it closed. When the ECU decides there is enough boost, it stops allowing the air from the turbo outlet from going to the wastegate actuator and allows it to go to the compressor inlet tube. The system is a pulse width modulated system meaning it is never “always on”, but instead cycled on for longer periods of time to increase boost, and shorter to decrease boost. When the TCV is off, air from the compressor is dumped to the compressor inlet, and the spring pressure in the wastegate is what regulates compressor outlet pressure.
This connects the manifold vacuum/pressure to the compressor bypass valve/diverter valve. This means when the engine is in boost, it holds the valve shut, keeping air flowing to the engine. When the engine manifold is in vacuum just after the throttle blade shuts, the vacuum pulls on the diaphragm in the CBV to allow the pressurized air to return to the inlet side of the turbo. This prevents turbo surge.