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FIXED AC vents don't blow going up hill[700/1989] posted by Don Willson on
Wednesday, 30 June 1999, at 11:10 p.m.
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
--'86 744 ZF xmission 120K miles, '89 760TI AW xmission 140K miles.
Re: FIXED AC vents don't blow going up hill[700/1989] posted by abe crombie on
Thursday, 1 July 1999, at 12:25 a.m.
Your solution brings up an interesting point.
If the check valves leak and allow pressure to enter the ECC's servos the Floor/Defrost and Recirc that have the rods sealed with boots would be very susceptible to the boots being dislodged or ruptured. Maybe replacing those on turbos at 75K miles would be wise money spent.
This doesn't explain the same failures on non-turbos where there would never be pressure available to be back fed into vac circuits.