Hello!

I noticed that ever since I bought my Monte about 2 months ago, when you go WOT or even a good 3/4ths of the throttle, my heat/ac/vent will change from going through the dash vents, down to the feet position. I see this is directly tied to the loss of vacuum as I'm accelerating. I did notice that in my engine bay there's a vacuum line, getting vacuum from somewhere on the UIM and going down to a little check valve, where one exit of the check valve goes into a wiring harness through the firewall, and the other exit of that check valve, has a short piece of hose and a screw jammed in the end.

This is certainly not factory, and I'm not sure where that plugged off exit on the bottom of that check valve is supposed to go. I think this may be the cause for my air position to change when I loose vacuum (and also possibly this tiny leak causes my very hard to notice, tiny, occasional missfire).

After finding this little check valve I looked for check valves online and found out that the one I'm talking about is refered to as the "Heat/AC Check Valve" so I really think I'm on to something here.

Here's a picture of the valve I'm talking about, it's normally located under the intake piping, between the battery and engine.


To clarify, I refer to both openings of the clear part of this valve as exits. It is the exit that goes down in this picture that is capped off.

If someone knows what else is supposed to be hooked up to this check valve where mine is plugged off, please do let me know. Any help is appreciated!

 

IIRC...one side goes to firewall, the other goes to a vacuum ball in the driver side fenderwell/bumper area, the last port goes to the engine.

 

Well so far we're both exactly right. I got a new check valve and put it in and immediately the problem with the direction of air changing has almost completely gone away. I suspect it'll be like brand new once I find the vacuum reservoir (I'm lazy).

Anyways, thanks a lot for confirming my suspicions with the check valve, and giving me somewhere to start with the reservoir.

 

Yeah, I lost my vacuum ball when installing the front kit... Just capped the line with a screw, and my blower works fine on all settings... Other people have said otherwise, guess I got lucky.