So I tried as best I could to describe my problem (?) in the title, but recently - and moreso when the car is cold, when I depress the throttle, there is a corresponding increase of air that comes through the window defroster vents. There doesn't seem to be a corresponding increase through the side window vents, so I'm not sure that is what's actually happening, but that is sure as hell what it sounds like.

Now, I know my 300ZX has this built into the Auto Climate Control system - it would NOT pump air out through the dash until it was warm (ie so your windows were always defrosted first, and so it didn't blow cold air on you) but I didn't notice my 7 doing this before and now it's very noticeable.



Any thoughts?

 

Bump

Anyone? Is this some sort of vacuum link? I'm finding it hard to trace because the problem is predominantly when under load, so i can't really drive and check at the same time lol

 

Did you add any accessories that take electrical power? Sounds like an increased load on the alternator so when you press on the accelerator the alternator supplies more power so the blower fan speeds up!

 

No....our system isn't vacuum actuated.

I concur with the above suggestion that this is because the blower is speeding up because the alternator is turning faster. Do you have underdrive pulleys installed by any chance? They will cause this behavior.

 

The blower might not actually be speeding up, that's just what it sounds like. It's really hard to explain - but that's what i thought it was at first.


I haven't added any accessories that take electrical power, it started doing it right after I installed my BOV.

 

And sorry, no - no underdrive pulleys installed.

 

It definitely sounds like a voltage fluctuation. Alternator might be on its way out.

 

Good to know.

Thanks for the feedback guys - it helps. It's reassuring to know that everyone seems to be more or less on the same page and that the problem isn't going to be some catastrophic failure.

 

Actually if it makes a difference - I put more thought into this on my way home tonight

the increase in blower speed is correlated to the degree of throttle and not the RPM. If I apply a lot of throttle, I get a lot of air, but at high RPM and no throttle, I don't get the blower sound.

 

Just to rule another thing out here; is your HVAC system on REC air or Fresh? I know in many of my cars, even if I have the system on off, air will blow through the system under load (with the system set to fresh air). If it continues when the system is set to REC air, then you can move to the next area to trouble shoot. As you have explained your situation further, I am tending to agree that the alternator may be on its way out. It sounds similar to what I would hear when my alternator was on it's last leg in my old FC.

I would say, take it for a ride (with the system on REC) to Advanced or Autozone. If this setting solves your problem, great. If not, your right there to have them test out your alternator. Two birds, one stone. Heck, even if it does solve the problem, can't hurt to have them test out the electrical while your there anyhow.

 

Good point - I'll check that out when I head home in 90 minutes, but I'm pretty well positive that it's on fresh air and not recirc.

 

Try it on the recirculated, that's the setting that will close off that airflow that sneaks through even when the system is off.

Again, from your further explanation of your problem, it sounds a little more dramatic than this, but it's a place to start.

 

Did that last night - the sound is still the same.

It might not actually be air coming through the defroster (I'm not limber enough to drive and reach, my fiancee says she can't feel a difference) and there's no increase in air coming out the side window defrost vents - which are piped in together.