Definitely not the case on euro S/V40's like my 2.0T.

The reason it only needs to run a little while is that the variable valve system used by Volvo that causes the reduced vacuum only operates on a cold engine and is only used to reduce emissions (and not for power gains like VTEC, VVTi and other such systems). Once the engine warms up it returns to 'normal' operation and enough vacuum is produced for the brake booster.

You can hear the pump start when you discharge the stored vacuum in the brake booster by repeatedly pressing and releasing the brake pedal until it goes 'hard' and then start the engine. (You need to do this as the pump won't even start if there is enough residual vacuum in the system.)

The pump makes a low booming/buzzing noise (not to be confused with the fuel pump, which can be noisy too) and it switches off after a while.

Because of this it will usually only run at the first start in the morning. This is also what causes the problem as it 'sucks in' a lot of cool/cold air that's often loaded with water vapour. Once the pump shuts off the vapour condenses inside the pump.

This can then cause the pump to either seize up after a while or generate a short. In both cases it will first blow the fuse and after a while it often needs replacement.

It's a bit like old EGR and air-pump systems that also suffer from similar problems with water collecting in the valves/pumps.

Bye, Arno.