When I replaced the wiring harness on my 760 a few months ago, I noticed I had a leftover vacuum hose with a little strap with a hole attached to it. Well I finally figured out where it goes (don't know why I didn't look under the hood of my 740 earlier). It is the vacuum supply hose for the heater control valve. But SURPRISE!!! no heater valve. The PO removed it and plumbed it straight with a small length of copper pipe.

My question is what would be the symptoms of the missing valve and open vacuum line? Car has ACC.

Replys are greatly appreciated.

My best guess is that the old heater control valve broke, and the PO just plumbed matters straight through as a temporary repair until he got a new valve. Then he decided to just trade the car and never got around to replacing the valve. The straight through plumbing is a common "first aid" kind of repair. For winter driving, I doubt you would tell much difference with or without the valve, but I would get a replacement soon. They are cheap from IPD, and easy to install.

The heater valve is a pretty common failure part on all 700/900 cars and you should simply replace it to restore everything to proper operation. They aren't too expensive and the new ones are superior to the originals. Typically they fail right after an overheating event of any kind.

Good luck with it.
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Rob Bareiss, New London, CT 86 244, 87 244, 88 744

The PO on one of my 700 series did the same thing --- discovered why. He had a leaking heater core and decided to bypass rather than replace. So, if and when you replace the valve and hoses, watch for water leaks.

dick
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93-940T + 91-940SE + 87-740GLE = One Happy Volvo Garage!

Symptoms: slightly lean mixture from the vacuum leak, and the heater is controlled only by the air mix door. In the summer your car must be hot on startup. The airconditioning will work overtime to cool it down.