So today I had my Air Con serviced. Nice and Cold! However, it brought to light the vacuum leaks which I had suspected for some time. Upon acceleration (and increased vacuum) the air velocity slows to a veritable dribble.
Where to start?
The vac one way valve in the engine bay
After that its stuff under the dash
Haven't had too much time to check things out, however, what I have noticed is that after driving when I turn the engine off, there is a distinctive hiss come from the passenger side front bumbper/ wheel well area. Is this where the vacuum reservois is located?
Very common fault on 700/900 series, both my S90's does it too. Vacuum leak can be anywhere but most likely culprit is the air recirculation bellow under dash behind glovebox which unfortunately is NLA for RHD models. LHD part still available and I've seen a friend of mine modify one to fit his RHD car.
Even with recirc off it still looses flow under throttle?
Possibly, the friend I was referring to is on his 4th recirculation bellow (94 model 960) so I'm guessing it's very likely causing the system to leak. But start with the check valve in the engine bay first, it's easy to get to & cheap to replace.
I can hear a his in the passengers footwell too.
Mine hises after I turn the car off. It's a VERY common thing to happen as the KM's go up I reckon.
There is definately a leak in the recirculation system. Will and I changed over the alarm system to the UK variety on Saturday. We had the lower dash apart and could feel the air leak in the passengers footwell with recirc on. I think there is another vacuum leak in the carbon canister as it also hisses from that area afyter shut down.