Hello all. I have a 2003 Dodge 1500 conversion van. I'm having a problem where all air goes to defrost vents when the vehicle is under the slightest load whatsoever. Could there be a vacuum leak somewhere? I know that in the past this type of issue was commonly caused by a check valve. Could that still be the case? If so, where could I find that valve... would I have to take doghouse off? Also, just out of curiosity, does that valve control vacuum to anything else? Your help is greatly appreciated.

 

Yes it's the check valve or a broken vacuum hose going to or coming from the reservoir. The reservoir is a round black ball looking thing behind and under the passenger headlight.

As for the check valve, remove the doghouse and look for it on the hose coming out of the passenger side of the intake manifold. Pay attention to it's direction before removing it because it only works one way.

 

Thanks for your help. I found the check valve. Wasn't sure how to check it's operation, but I figured that since it's a one-way check valve that you shouldn't be able to blow through it in both directions, which I could not. So, does that mean the valve is OK? Also, all lines appear to be in pristine condition. I should also mention that along with this my cruise control has trouble maintaining speed under the slightest of loads as well... could these two issues be related?

 

Yes, if you can only blow through the valve in one direction then the valve is okay. This thing with the CC along with the other problem indicates a significant loss of vacuum. Check the rest of the vacuum lines and double check the reservoir for any leaks.

 

Well, here's the latest. I checked all vacuum lines and did find a hard vacuum line coming off the throttle body that was cracked, so I replaced that one. After all was said and done fired it up and noticed that the problem with the air still exists, under load pops over to defrost vents. Also, I've now noticed that I only get air from either the floor vents, or the defrost vents, no matter what the setting.

 

Then you still have a leak somewhere. The fact that you're having a problem getting the air to blow out of the vents sounds like the vacuum actuator under the dash might have a ruptured diaphragm. I can't tell you exactly where to look for it, but if you remove the engine cover and the glove box, you'll get to see a lot more of underneath the dash.

 

Any idea what this vacuum actuator looks like? I'd like to know that I see it when I'm looking. Thanks again for all of your help

 

See the thing at the bottom of this (generic) picture that looks like a tilted flying saucer with the vacuum hose connected to it...it'll look like that or very similar.

 

OK, I think I know what part you are talking about now... hopefully it's not as difficult to get out of there as it looks

 

OK, here's the latest. I actually stumbled upon the fix for all of these issues.

First, about only having air through the defrost or floor vents I was checking the oil the other day and happened to notice a vacuum line that I must have accidentally disconnected when messing around under there. Reconnected and problem solved.

Now, as for air popping over to defrost when under load I think I've fixed that problem as well. Oddly enough I think it had to do with the cracked vacuum line between the throttle body and evap canister. When I replaced that line I did not use exactly the same thing. What I used to replace it with was much larger in terms of diameter, instead of a small diameter line with larger diameter connections on each end. What I had done clearly wasn't holding vacuum properly as I go a check engine code that pointed to a vacuum leak somewhere between the engine and evap canister. So, today I decided to head to the salvage yard and pick up exactly what it what that I'd replaced. So, got it home, popped it on and took the van out for a test drive and not once did the air pop over to the defrost vents when under heavy acceleration, and believe me I went WOT as often as possible just to make sure.

I guess the lesson here is that it's very important how you replace some of these vacuum lines. And, that in the future I will remove that particular line when replacing my spark plugs because that's how I think I broke it in the first place.

Again, thanks alot for all of your help alloro!