[FrEaK_aCcIdEnT]

I didn't notice this until a couple weeks ago. I usually leave the recirculate button pressed in. One day I had the fan setting on 0 (off). I was cruising at hwy speed. I could feel air coming from the vents. I looked at the controls to confirm it was off. I noticed the recirculate button was off. I dressed it and the air stopped coming in the cab through the vents.

What would be malfunctioning to let air in when the HVAC is off but stop the flow when the recirculate is activated with the HVAC off?

I just leave the recirculate on to keep unwanted air from coming in when the system is off. Just a nuisance right now...

 

[cart7881]

I don't know if this excerpt from the 2011 Service Manual has any bearing on what you are experiencing: "The recirculation operation can function with the blower motor in either the ON or OFF position. Recirculation is not available in Defrost and Mix-Blend mode".

 

[FrEaK_aCcIdEnT]

I don't know if this excerpt from the 2011 Service Manual has any bearing on what you are experiencing: "The recirculation operation can function with the blower motor in either the ON or OFF position. Recirculation is not available in Defrost and Mix-Blend mode".

Appreciate the response. I understand not having recirculation on blend and defrost. It keeps letting air pass through the system when the system is off and the recirculation is also off. If the system is off and I have the recirculation on then the air is blocked from freely entering the cab as it should be when the system is off.

It isn't a pressing issue, just one I would like to figure out.

 

[Z71 4x4]

If I understand your question correctly. When recirc is on the blend door behind the glove box is closed to the cowl inlet . When it is not on recirc. you are getting fresh air from the cowl . So basically with no fan on you felt ram air coming from the cowl.
Open your glove box past the stop pins with the key on and operate the recirc button . You will see what I mean. We have no cabin air filter to slow it down.
True there should be another door for say mix that I can't confirm for ya.

 

[cart7881]

The recirc door is referred to in the Service manual as the "inlet valve". If the recirc button is out, the motor drives the door open and you will get some airflow anytime the vehicle is in motion. The only way to block the airflow is to keep the recirc button in. It doesn't matter whether the fan is on or off or if the A/C is on or off. Turning the fan or A/C off does not change the position of the recirc door.

 

[FrEaK_aCcIdEnT]

Oh, wow. Thanks for the clarification! The nuisance is normal functionality.

 

[Z71 4x4]

Right that the point I was trying to make. I just wasn't sure if the mix (hot or cool) lever operated another door as I have not had that much of the heater box apart. Hope I never have too either!

 

[cart7881]

The Temperature knob operates only the Air Temperature Door. The Mode knob operates the Mode door and the Defroster door using a cam. Yes, repairs to the HVAC Module are a nightmare.

 

[FrEaK_aCcIdEnT]

Ok, how about this question. Is it also normal for the temperature knob to be stiff? When I move it to full cold or full hot it never stays full how or full cold. It's like it ever so slightly moves back a fraction of an inch. Like the other issue, not a real issue, just a nuisance.

 

[cart7881]

Yes, That is also normal. I remember some Threads a while back where Members had experienced problems with the linkage and it was determined that forcing the control knob past the stops was the cause. Apparently the stops are on the door end, so continuing to turn the knob puts stress on the linkage.

 

[djb383]

Years ago GM called the constant air flow into/out of the cabin (when the vehicle is moving) "Astro Ventilation". A small amount of fresh air circulates in/out when the vehicle is moving even when the HVAC is completely turned off.

 

[FrEaK_aCcIdEnT]

I remember my s10 doing it and I replaced my vacuum line going to the vacuum reservoir on the driver fender and it fixed it. But that one didnt hae recirculate. So I thought maybe there was something else to it. But if it is normal, it is normal.