Finally replaced the heater valve. The hissing noise was there before so I thought I would find a hose disconnected but couldn't find it as I crawled around under the dash. Can someone think of a way to duplicate vacuum from the engine while the engine is not running? If I can do that I think I can track down where a vacuum hose for the heater controls is off.

Thanks,

Kris

I've found the HVAC flap vacuum chamber, that holds vacuum for all the under dash flap motors, when you press the Floor- Windshield Demist- Reciculate, can leak at either end with out much bother.

The three square flap control buttons:


Or at the switch itself:


See #34 in the image, that vacuum chamber, with the vac line connection at either end:


I used some sort of 3M or other adhesive sealant to secure the lines on my 240s as over time, the bac line connection ends, like they do in teh engine bay, sort of lose their grip, and, if enuff slack, a nip, a clean with 91% isopropyl alcohol, let dry, and some adhesive sealant, and let dry, makes for a good seal on the hvac vac motor flap control control line under the dash.

One clue, is that when you are highway speed motoring, and only have fresh air come in, that when you floor it, intake manifold vacuum decreases, and you lose fresh air intake, only to have fresh air come back instantly the second you take your foot off the gas pedal.

Though also ensure the one-way vac line check valve at the intake manifold (black and whit check valve at 3 of the clock in this email here:



Allows the engine vacuum to suck in atmosphere into the air intake manifold, yet not the other way. (I have two of these one-way check valves on a Volvo 240 or two. These check valves do like a good clean sometimes with isopropyl alcohol so they seal well.) Mine keep vacuum overnight.

And follow what the other respondents say to your original post.

Sorry to go on so long.

Questions?

Hope that hep-kats (helps) you and your mighty 1989 Volvo 240!!!!!

Buttermilk MacDuffy's Tavern (Fresh cultured buttermilk, and other fermented dairy products served since 1977! We have a cheese problem!)
--
Jonathan Harshman Winters III: The Mightiest, Greatest, & Most Powerful North American Comedian & Comedic Actor in Perpetuity

I like your shifter!
Dan

Ok. Thanks to all the responses! The diagram is especially helpful!

And it is a mighty car! My wife and daughter both bought newer cars and I have driven them somewhat. However there is just some intangible positive feeling I have when driving my Volvo wagon.

Once I fix the vacuum leak I will continue the search for a set of Virgos.

With appreciation ,

Kris

I had this very problem in my now-deceased '89 wagon. The culprit was the check valve on the intake manifold. It is the half black/half white cylindrical object with a vacuum hose coming out of each end. You can see it in the last photo in the earlier post.

Pull it off and see if you can blow in both ends. If you can, then it needs replacing.

Solved! It was the check valve! Thanks to all your help.

Yup. I was going to chime in and mention the Check Valve. Glad I read your last post. It sure does sound like it's under the dash and not under the hood, doesn't it?
--
'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

The noise you hear from under the dash is the vacuum released from the reservoir located there. Normally the check valve holds the vacuum when you shut off the engine. The small tube on the check valve goes directly to the vacuum reservoir under the dash.

If the hissing sound was continuous when driving, I would suspect a leak but since it only made the noise when shutting the engine off or hard acceleration, the check valve is usually the culprit.

OK. Thanks jstraw, will do!

Are you sure it's not the brake booster leaking?
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Hmmmm, vacuum pump? I would get a used one off CL and resell it for what I paid.

That said, have you tried all the combinations on the air director to see if the hissing goes away from one of them.