At idle and cruise, whether in "Normal" or "Max" mode, I've got adequate air coming from the vents. Under moderate to heavy load, however all air comes out of the bottom. Based on how manifold vacuum behaves in an engine depending on RPM, what's going on makes sense. However, in Phoenix in June, it's annoying as h#ll. I replaced the vacuum ball under the hood last year and I could find no vacuum leaks from the lines under the dash. I was thinking of adding a little electric vacuum motor to help maintain as much vacuum as possible, but if there is a problem, I'd rather fix it than compensate for a problem.

Anyone else have/had this problem?


Thanks in advance!

 

Sounds like you have your vacuum hooked direct to the motor. And don't
have a vacuum canister. DO YOU HAVE A CHECK VALVE BETWEEN THE BALL AND ENGINE

 

If the car in question is the 82 Delta in your avatar (next time, please specify the car) then yes, you have a vacuum leak problem. The default position of the flapper doors inside the HVAC box if there is no vacuum is floor and defrost vents. As noted above, it sounds like the check valve between the engine and the black vacuum storage ball is not working properly or is missing. The other option is there is a vacuum leak in the hoses or actuators somewhere that let the vacuum level drop too much at wide open throttle.

 

Thanks for the replies! I'm sorry I didn't specify the car, but it is in the signature. I'll try to remember in the future. In the case of the vacuum line from the engine to the ball, there is no check valve that I can see and I don't think there ever was. The vacuum line is a black plastic hard line with rubber ends. Where would the check valve go? I though the purpose of the vacuum ball was to be a reserve and check valve. Any part numbers or pictures?

 

I own a old school parts house. I can send you a pic of the valve. It keeps the vacuum in the ball so you can use the a/c right. Let me give you part no. In motormite. Tomorrow and you can pick one up they are cheap under 5 bucks
it will fix your problem.
Rich

 

Thank you so much!

 

I agree, on a stock engined 82' Delta 88, you should have plenty of vacuum availible. For cars running hot rod engines, with high overlap camshafts, this can be a problem though. Some have been known to use aux vacuum pumps or larger canisters in this case. My custom 455 car's running a secondary canister. Vacuum's always highest, when cruising with the carb throttle plates mostly closed. Sounds like "OLSMORAT" is helping you out here, but I'd at least temporarely install a vacuum guage, to help you diagnose the problem. A canister only stores the highest vacuum it see's, but does nothing to generate vacuum in any way.

 

I'm going thru the same thing on a 93 F150- for a while, under steady cruise it would still blow thru the dash vents and default to defrost under acceleration, so it's obviously vacuum related. Now it's consistently defaulted to the defrost vents. I figured vacuum storage ball or rotted hose, but I don't see a vacuum can anywhere on this truck unless it's behind the dash. There's a weird vacuum "splitter" (for lack of better word) valve in the underhood vacuum harness. Possibly a check valve?

All my daily drivers are Fords now, so I guess I need to learn how they work.

 

Fords us a in line check valve that can crack and separate. They are cheap, the hardest part is isolating which one is the culprit. They are usually black on one end and clear/white on the other. They are shaped like a funnel or a spinning top. You can check them by blowing through one end and then sucking through the same end. If it's working properly it will allow air in one way and not the other.

 

Vacuum leaks can be a real pain, and good idea getting a Mityvac hand pump tool w/gauge. These can be real time savers tracking down leaky HVAC vacuum motors and such. I also have an electric refrigeration vacuum pump, so I can run a hose from it inside the house, for a quiet test enviroment. A stethoscope's also a good idea. The Mityvac I have, is the Silverline kit with small canister for bleeding brakes. Nice tool, and also pumps pressure out of the top vent port.

 

The check valve is Dorman P/N 47150. The LH port in the photo goes to the manifold. The other two go one to the vacuum ball and one to the A/C vac feed hose.

 

Thanks for getting me on the right track so quickly. That's got to be the problem. I have a hazy recollection of testing all the A/C vacuum lines in the dash. All the ones that should hold vacuum (i.e. connected to actuators) did.

After looking at the part, I went over it in my head and I couldn't figure out how it would hook up. Is there a tee fitting missing somewhere? I drew a quickie diagram of how it's currently set up and another of where my confusion lies.

Based on what I came up with, wouldn't a check valve with one port on each side make more sense?

Thanks again!

 

Now I see the problem. All the 77-90 cars I've seen use a vacuum ball with a single port. The purple line hooks up to the third port on the valve I showed you. If your vacuum ball has two ports, it may already have a check valve built into one of them, in which case, you need to ensure that the manifold hose goes to the port with the valve. If you have a two-port vacuum ball with no check valve, then yes, the two-port check valve on the manifold hose is the one you want.

 

Many thanks to everyone and Joe, who has probably forgotten more about Oldsmobiles that most will ever know!

 

Just wanted to give an update.

Ok, so the plot thickens. I went underneath the dash last night and tested all the vacuum actuators with my Mityvac. It took a bit of pumping, but they all worked. They did NOT, however hold vacuum indefinitely. I pumped each one down to 20" hg and after two minutes, they had dropped to 17" hg. Either they are all good or all bad. I'm leaning towards all good. I also tested the vacuum lines going to the actuators, no leaks there either.

Sounds like the next step is to see how much vacuum this tired 307 is actually making! I'll also test the vacuum ball and lines going from the ball to the dash.

Have a great week!

 

Glad you're making some progress. You probably have some small vac leaks in the control head. I'm thinking 7-10" vac should be plenty to move those vacuum motors.

I got the F150 straightened out by replacing that "splitter" thing which was indeed its check valve. Natcherly the original p/n had been superseded and the one I got at the Ford store is similar to the Dorman piece Joe posted. 8 bux was cheap enough.

Also found where Ford put the vacuum storage tank. It is part of the evaporator box.

 

Sounds like you're HVAC vacuum motors are ok, as if really bad, wouldn't hold any vacuum at all. Loosing a few inches of vacuum over time, could be a test connection, or the diaphram just settling in a bit.

 

Sure your vac pump is not the leaker? I got one before and after a few uses, it will not hold a vacuum. I use my own vacuum source now.

 

Do you mean the mityvac pump? It's possible, but I'm confident that the actuators aren't the problem. I might have an issue in the control head. I'll check that out, too. The car doesn't have it's own vacuum pump. Now if you are referring to the tired 307 as the pump, then sure it's a leaker!

 

Yes, your handheld vacuum pump. The one I got was a POS. I am back to using my mouth - lots of vacuum there...

 

Well, quick update. I haven't check the overall vacuum the engine generates, but I used the mityvac to test the line going from the manifold to the vacuum ball. Connecting one end to the mityvac and holding the other end closed with my finger, it seemed to lose vacuum pretty fast. I took a new piece of rubber hose and tested that, it held vacuum much longer. I'm guessing the mityvac may have a slight leak. I replaced the black plastic hardline with a rubber hose between the manifold and the ball and it seems to be working a lot better now. At highway speeds and under load, the air flow doesn't drop to the floor vents. While I was at it, I also replaced the rubber connector from the purple hose to the ball. That seemed to further help.
When I'm running on MAX, I still feel a slight trickle of air from the bottom vents, but it's much better now. I'll have to check the control head to see if anything is leaking there, but thanks for everyone's help!

 

Great news!