John,

My 90 765 has the same set up. The check valve with white hose goes to firewall passenger side. Other check valve has black hose (same size as white one) and goes into firewall next to white one. I'll look under dash to see where it goes. I suspect to a vacumn canister.

There are check valves because with a turbo there is not always vacumn. When in boost conditions there is actually pressure in intake not vacumn.

Joe

John
your setup looks like my 89 745gl, the hoses you have upfront there, the one with the T is the vacuum system, you should be able to find the vac canaster in the front bumper guarded by a plastic casing which you have to rip out and even see it, they may have moved it to the inside of the car on the 90 760 model, the T should branch off to the canaster and should have large hose which will then have a connection to a very small hose which since when i looked i couldnt see but it headed towards the back of the block area, the other hose with the check valve looks like someone added that in when trying to chage hoses, since that it a typical volvo hose that they used on the Cruise Control, that should be pugged in with a adapter J shaped to the very bottom connection on the manifold there cloest to the front. this is how mine is setup anyways and it looks like yours would be set up the same even though its a turbo, my center vac connections are blocked off, yours wouldnt be because you have a turbo. i hoped this might have helped you in some way.

Looking at wife's 940 SE, there are two check valves and the whole mess is on a T. with only one manifold attatchment. No vac pump that I see and the car is a 91, so should be similar. If you want I can shoot at pic and email it.

dick