hvac vent question

[pmf2]

Please forgive me for any mistakes in my terminology… I was not able to find any previous posts on this-I have a 97 q45.

For some reason I remember that I can have the AC turned off completely and turn the climate control all the way to the cold side, I would get some cool air coming out of the vents by my face. If I were to turn it to the warm side, I feel warm air coming out from the vents by my feet.

Now when I do this, I only feel the air from the vents by feet, irregardless of the temperature setting I chose.

When I turn on the AC, and I change the temperature it automatically changes the vents appropriately.

Any ideas how what can be wrong???

[Q45tech]

Sitting still or driving down the road with air being forced down cowl and into system?Even with system off short of duct tape over inlet vents [below wipers] some air will flow.

People complain outlet air is hotter than radio [weather report] yet they fail to measure the hot road or hotter engine compartment or the added heat from fan motor.Generally ac must be used when weather report is 65F or above.

[pmf2]

Hi Q45tech,

I tried both. I know when the car is moving- I think above 40mph I can definitely feel the air blowing by my feet. I do understand the aspects of the temperature of the air coming through the vents, but I remember feeling air coming from the vents by my face. I actually remember feeling it more when I have my sunroom vented open, and that may just be the dynamics of air flow through the car... but for the life of me I remember feeling air through the vents by my face. I am not too sure on how to read the FSM to determine if I am just imagining it, or air is blown through those vents and there is something wrong with my car.

Thanks for your help.

[Q45tech]

Think of the chimney effect [when sunroof is open] the interior air rises and sucks in replacement air from the cowl.Just a normal operation of every vehicle some more than others. Some HVAC are always on lowest setting of fan motor to provide fresh [outside] air .........................just passing by a warm fan slow turning motor raises the air by 600 btu per 50 watts [ 3.5 amperes]. A 70kg human at rest creates 250 btu of heat.

40 mph is serious speed ..............53 feet per second less the restrictions is what the air should move out the vent.............obviously lots of restrictions.

[pmf2]

I completely agree and undertand.

But should there be any air coming out from the face vents? that is what is bothering me the most. I remember putting my hands to the vents by my face and feeling air when set to a cooler temperature, and from the floor when set to a warmer temperature.

I understand and agree with how the air is travelling, but is there some sort of diverter/door type thing that gets activated even when the system is off that is malfunctioning?

[Q45tech]

Study FSM HVAC section for detailed explaination.

[maxnix]

But should there be any air coming out from the face vents?

...there some sort of diverter/door type thing that gets activated even when the system is off that is malfunctioning?

Set your vents to upper only and you will know.
Modified by maxnix at 8:34 PM 5/11/2009

[pmf2]

I can set them to upper only and it works perfectly. When using the system on auto or econ, or even just turning on the blower, the mode door motor works perfectly. Which makes me assume that all the other sensors like the sun sensor, ambient air sensor, etc are working correctly. But the more I read the FSM I do believe that the mode door motor should work when the system is completely off and you just change the temperature on the dial- but I may be wrong… I don’t see it explicitly saying it does or doesn’t.

Not sure what else might be wrong...

[maxnix]

Don't know why you are worried about door operation when system is switched to off?

[Infinitiguy19]

The best way to prevent fresh air from entering the vehicle through the Heating/Ventilation Air/Conditioning (HVAC) system is to set the display to Re-circulation mode. You can do this via a button on the display but on the 1990-1992 Q45's you will have a green light lit up for ten minutes. On the 1993 Q45's the system will stay in re-circulation mode till told other wise (Press the button again to disable) or the ignition is turned off. Then of course the system defaults to fresh air again.

I was searching for some posts when this topic...