Cold air under dash when turning corners

Super lame title, but explains the issue.

Low ambient outside temperatures, Heater turned to windshield defrost. Heater not turned on for under dash area.

Result: Cold air on legs when cornering.

It seems like an HVAC damper is opening and letting cold ambient air in under the dash. Seems colder when turning to right vs. to left.

Question: Does this sound familiar to anyone else?

Does the HVAC unit have springs or vacuum actuators or similar on dampers?

Can somebody point me in the right direction for a schematic of under dash HVAC assembly?

Thanks.

I noticed that too on occasion when it's cold. I figured it's just related to moving my arms about when turning the wheel. Be interesting to see what you find out.

Totally normal, unfortunately. Everybody I know has this same problem.

pparks1 said:

Totally normal, unfortunately. Everybody I know has this same problem.

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Different temperature (hot air rises, cold air sinks) air in a moving vehicle, going around a corner- fluid dynamics 101.

Same effect when you open a door in winter. You feel the cold on your feel before you do on your face.

Nothing is wrong, change your settings to put some on the floor and this will stop.

Regards

For the first eighteen months or so I didn't experience this problem. I started to notice the cold air issue while turning corners in late fall of last year. A few months later the upper vent on the passenger side of the car started to blow cold air. It was later confirmed by the dealer that the source of the heater problem was the heater core. After it was replaced, the cold air while turning a corner issue was eliminated. Coincidence?

1alfie said:

For the first eighteen months or so I didn't experience this problem. I started to notice the cold air issue while turning corners in late fall of last year. A few months later the upper vent on the passenger side of the car started to blow cold air. It was later confirmed by the dealer that the source of the heater problem was the heater core. After it was replaced, the cold air while turning a corner issue was eliminated. Coincidence?

Click to expand...

Totally different situation from the OP, same outcome though. An imbalance of different air temperature.

Glad you got it fixed.

Regards

Basic fluid dynamics. The cold air settles into the foot wells and sloshes (for lack of a better term) around when you turn corners. Using defrost + floor instead of just defrost will help alleviate the problem.

When I did my heater core install I removed the undersized foot vent pipe assembly and the plastic pan under the dash on the driver side. It seemed to help with this issue substantially. Now my foot heat just blows out of the airbox connection down toward your feet out of the large 2x3" duct

Had this issued from day one.

I don't buy the air sloshing around on the floor explanation; air is not a liquid. Cold air is getting in somehow.

If you turn the selector to heat the floor, after defrost is done, the problem seems to go away. Fortunately I do not live in a very cold area so it's no bother here.

Yeah, I don't buy into the fluid dynamics argument. Air handling and exchange takes time. The warm air around my legs doesn't dissapear into the dash or up to the windshield in the fraction of a moment it takes to go around the corner.

I suspect a fresh air damper does not have enough tension (spring or vacuum) to resist my 'High' G loading around the 6 fast corners here in Kansas.

My legs are at a comfortable temperature when I'm cruising. I don't want to adjust the temperature to bake them out for a brief few seconds.

Also, I am not familiar with this occuring in the many vehicles I have driven or ridden in. It is not a natural function of a satifactory HVAC system.

Anyway, Back to original question. Whom of us has a schematic or picture of the underdash HVAC ducting and dampering assembly?

How can you guys not buy the fluid dynamics argument? If you have cold air in the footwell, and you're heating the air through the defrost (but not the floor), you're going to develop a pretty strong temperature inversion. That cold air mass will absolutely behave like a pool of liquid sloshing around as you turn corners.

Don't believe me? Introduce smoke or vapor into the cold plume of air and watch it.

Turning the floor heat on will help reduce this phenomenon since it prevents the temperature inversion.

Imagine the cold air in your footwell being the fog in the Grand Canyon in this video: https://www.youtube.com/watch?v=J34fRtfCRWg

Simple as HOT air RISES....COLD air FALLS!

Yes, air is a fluid, although it has different properties from liquid fluids. For example, you can compress air, but fluid (such as water or oil) has little to no compress-ability.

I can remember riding my motorcycle home after working a late swing shift at Boeing (around 3AM), and could feel sudden changes in air temperature as I rode on the freeway into depressions and back into higher elevations. And we're only talking about elevation changes of 10s of feet, not significant grades.

Air is a fluid! Buy it or not, it's true.

Take a Helium filled balloon inside the cabin and head down the road. Go into a curve and the balloon will shift to the inside of the curve. The reason being that the heavier air is being forced to the outside.

In the case of cabin heat the theory remains the same. Warm air being lighter than cold, the warm air will migrate to the inside of the curve or turn. Unequal cabin heat between sides really amplifies the problem.

I noticed this early in the winter and thought little of it. Then an almost total loss of heat on the passenger side. After having replaced the core I realize that cabin heat was generally degrading and that I was unaware. As of last week I very much doubt that the cold air shift would be noticeable, except possibly in the coldest conditions with the cabin only partially warmed. The difference between a partially blocked core and a new unit is amazing!

PaulB said:

I don't buy the air sloshing around on the floor explanation; air is not a liquid. Cold air is getting in somehow.

If you turn the selector to heat the floor, after defrost is done, the problem seems to go away. Fortunately I do not live in a very cold area so it's no bother here.

Click to expand...

Air behaves as a fluid. It's science.

http://youtu.be/y8mzDvpKzfY

I'll have the air on fresh (not recirc), vents set to defrost & foot, nice and toasty after 30 minutes driving to work. Drive around a rotary, puff of cold air on my feet.

There is a damper in the trunk to release air pressure when you close the doors. I think the damper opens in the turn just a little, pulls a small vacuum on the fresh air intake = cold air on feet.

Of course its science and air is a fluid. The video posted by Nebelwerfer is about the simplest explanation you can get.
You might have some other thing going on in you car but the basic fact is that air moves and behaves in a certain way. Whenever you change the direction you are driving, air will be sloshing around in the car. If you are driving in a straight line as I imagine you do often in a state like Kansas and just pumping warm air to the top half of the car, a sudden turn will result in this action.
If you truly think it is more than normal then check along your firewall, door seals, the trunk air damper, etc to see if anything is out of order but I am willing to bet that stuff is fine and you are just more sensitive to the air sloshing because your senses are heightened after experiencing more of a temperature change than normal.

Nice video; however, think about it. The video had the balloon keeping the air and helium separated. This case has warm and cold air mixing all the time, so the difference in density is much less. Also, if your explanation is the correct one, then going around a right corner will make your feet feel colder, while going around a left corner will make it feel warmer. Accelerating will make your feet warmer, while braking will make them colder. Not only that - you would feel it with your face just as much as with your feet. So, I still don't buy it - there might well be some very small effect, but not enough to detect it on our skin.

Wow, who knew a fresh debate was possible given the 4 year platform life.

Clarification:
1. I do drive with defroster and no leg heat more often than not. I feel it keeps the chill of the windshield off my face.
2. I set the passenger temp and driver temp setting to the same climate control value.
3. I have not replaced the heater core (though I have one on the shelf, thanks Goodwill Package) nor even tested the temperature gradient between passenger and driver leg compartments.
4. I do notice a difference in temperature between a right hand turn and left hand turn.
5. I notice the cold air directly on my shins (left leg more significantly than right, I believe), but have not even looked under the dash to confirm the location of the vent. (I'm lazy, and not too worried about the issue.)
6. It's warming up here, so this discussion is becomming a moot point for at least 9 months or so.

But given a long enough time driving down the road to allow the air to mix and get to a relative equilibrium temperature. There should not be a blast of cooler air like the flip of the switch. Air is a fluid and had mass, but cannot slosh around as stated above, with the time durations we are talking about here.

I can appreciate Nords response regarding the effect of unequal cabin temperatures between driver side and passenger side.

I do not buy the inertia theory. My '13 blows hotter air when I turn left, and I get cold air when I turn right. I use the vent and defrost or just the vent. Speed does not change it. Cornering at 5 mph or curves at 80, same problem. Warm air blows on my face. Cold air as well.
My son's 14 does not do it, neither did either if my other '13's or my '14. Dealer replaced the heater core back in August. I will be getting another appointment this week as it is still under the CPO warranty and I will update as things change.