I have asked this before and I can't solve it. When going up hills or under hard acceleration I loose the air flow throught the upper dash vents (1989 740 8 valve non turbo) I have been led to believe that it is a vacuum check valve under the hood but I do not seem to have one. I have a t fitting near the brake booster that has a small line going through the firewall but no valve in this fitting. The local Volvo dealer doesn;t seem to know the answer either. I hope it is not the repair involving chopping holes in the heater thingy and laying upside down for most of the weekend though

The image is of an 88 744 Turbo. Circled in red is the check valve. Maybe the 89's is located there as well, then again....

Randy

Find the vacuum canister up by the radiator. Replace the hose from it to wherever. It is difficult to see and is often bad with your age of vehicle. Fixed my 740 AC right up. My 740 does not have the check valve whereas my 940 does.

The test by fixit 2003 should help point you in the right direction.

My '89 has a T connection in the engine compartment under the intake manifold back near the firewall. Can't see any checkvalve either. The heater vacuum line goes from there through the firewall and the other branch is a large stiff tube that goes forward to a vacuum resevoir cannister up near the radiator. Maybe your resevoir is not connected or broken leaking vacuum. After the engine is shut off you should be able to move the heater control back and forth and hear a slight vacuum hissing sound as the valves actuate. No hiss no reserve vacuum.

Like Rob sez, no check valve = your symptoms.

Manifold vacuum drops when the engine load goes up, as in climbing a hill. The check valve retains vacuum so the little valves in the ductwork stay as set.

Seems to me that having two check valves would work OK, so if you cannot find the one that's supposed to be there, put in another one.

Good Luck,

Bob

:>)

No, it should be under the hood. Maybe it broke, someone didn't fix it right, stuck a bolt in the broken off part, and just connected up any old vacuum lines with a T. Have a look at another engine if you can, to see what you're missing. I can take a pic of our 90 engine tomorrow for you. Should be a plastic disc in line with one of the hoses from the manifold. It's two layers, usually white and black or white and grey.

If it's missing, that would explain it.
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Rob Bareiss, New London CT ::: 92 244-M47-207K ::: 90 745GL-M47-268K ::: 88 245DL-AW70-230K ::: 88 244 SOLD! 87 244 SOLD! Still looking for a bright red or black 244 with sunroof...

I was at the pick-a-part yesterday and only one 700 series this time, I looked under the hood and they had the same set-up I did on an 87- although I did snag a new alternator for $20.00 so it wasn't a lost trip.