My 760 turbo quit blowing air out the vents when the turbo was neutral or in boost. I replaced the check valves with aftermarket ones and checked all hoses. No luck. Abe and others thought it was a blown diaphram in a vacuum actuator.

I took it to Carl Duke in Ft. Collins Colorado expecting to pay for several hours labor to replace these actuators. An hour or so later they called that they had replaced the check valve with Volvo check valves and all worked well.

Carl said that if the check valves are bad and the turbo goes into high boost that is what blows the vacuum diaphrams. So check those check valves. They are only a few dollars each. Make sure you point them the correct way.

Don Willson