Cold legs and other hvac oddities

[Cnixon]

I am about to raise a service request mainly due to cold right (leg closest to drivers door). Any one else had similar experiences. I know I will be given the 'its nominal' sir. Which I will deal with at the time! It has cropped up several times on this forum with both the Y and 3 with heat pumps. I can feel cold air even on hi temp hi fan. It was 1 degree this morning outside. Another issue is that the vent does not direct up like it did on my 3. Again mentioned elsewhere. Maybe the two are linked?

 

[M1tch]

Not had the cold leg issue but was never able to get cold air to my face - until one of the more recent updates. It’s was around Xmas time it sorted that issue out so I can only suggest latest software but I’m sure you’ve already done that.

When mine went in for the air not going to my face I got the “it’s normal sir” answer

 

[Billbrown1982]

Never had the cold leg issue either and I pretty much only wear shorts so guess i've been lucky.

 

[Fursty Ferret]

Interesting that you mention this as I've had some climate control oddities recently on my Model 3, particularly related to cold air on feet (to the extent that with the temperature set to 21.5C my feet go numb) so I'd be interested to see if the service centre find anything. Turning the temperature up another 0.5C fixes the cold feet but makes the car too warm.

 

[exlatccatsa]

I always have cold knees driving in the winter.. I never though of it affecting anyone else.. its not a door draught though, rather lack of directional warm air I think. Warm air on the feet and upper body, but cold air in-between?

 

[Cnixon]

Thanks. I cannot get cold air to my face. The display does nothing much beyond flat forward so that might be blowing down. I only notice the cold legs when its cold outside. Some in US say its ok when vehicle stationary.

 

[thax1]

Radiant heating in the new Lexus RZ explained

An alternative to conventional heating.

mag.lexus.co.uk

Lexus now moving to radiant IR panels for supplemental heat in their BEVs.

 

[Kansalis]

I get the cold legs issue sometimes on my M3. It seems very random & doesn't happen all the time. Just sometimes realise that my knees are cold, despite the general temperature inside the car being warm.

Thinking about when it happens, now that you mention the heat pump, it could be something to do with direct sunlight on the body of the car when the outside temperature is low. I did a couple of two+ hour trips this week in the rain & didn't have the problem. Sometime last week when it was sunny but chilly outside I did check the venting angle because my legs were cold...

 

[Fursty Ferret]

Thinking about when it happens, now that you mention the heat pump, it could be something to do with direct sunlight on the body of the car when the outside temperature is low.

Now that is is interesting because I've also perceived a link between the two. I wonder if the car senses the sunlight and cuts the heating back a bit on the assumption that passengers are being nuked inside the cabin?

 

[Ferret]

My HVAC blows cold from time to time, around the knees.

I had thought it was connected to preconditioning, maybe stealing some cabin heat to warm the battery.

 

[qwickshot]

I think that is happening is that when there is direct sunlight on the cabin, it’s likely the heat gain is more than enough to warm the air in the car above the temperature set.

The car will start cooling the cabin (normally heat scavenging and dropping it into the battery for better performance), when that happens the cool air may not be fully mixing and is probably sinking into the footwells and it makes sense that you get cold feed/knees.

 

[thewishy]

Just going to share an observation. These complaints crop up in the autumn and spring, and generally on heatpump models. In the winter the systems need to heat all the time, and work well. In the summer, they need to cool all the time and work well.
The difficulty is shoulder seasons, and I think it's just down to the ability of a heatpump to modulate itself when a small amount of heating is desired. It runs for a little, then switches off and the air get's a little cold.

 

[kelvin 660]

The problem I have, this time of year, is during the day when the sun is out it can get hot in the car. So you re-direct the air flow to your face to cool down. Then next time you get into the car it's at night and cold, so you have to redirect the air flow away from your face. Doing this when driving is not easy as you need to use 2 fingures. It would be good to have a button to switch between these 2 states. Or just the old fashioned manual adjustable air thingy that works so well in other cars...

 

[Cnixon]

Just had 2023.12.1.1 so will see if anything has changed. I am driving at 5am no sun, no face air and cold right leg, but at least I see I am not alone.

 

[Cnixon]

It seems that you can direct the air down really effectively (must be the aerofoils shape of the dash) and give yourself really cold legs! Even with the air directed fully up there is still a bit heading down. A flap (aileron ) seems to do the trick. On the screen side the air hits the screen and gets pushed down but that does not seem as bad.

 

[Kansalis]

I think that is happening is that when there is direct sunlight on the cabin, it’s likely the heat gain is more than enough to warm the air in the car above the temperature set.

The car will start cooling the cabin (normally heat scavenging and dropping it into the battery for better performance), when that happens the cool air may not be fully mixing and is probably sinking into the footwells and it makes sense that you get cold feed/knees.

This make sense, though it's definitely more than a "sense" of cold knees. Mine get cold to the touch as if AC is blowing at them. I usually have my climate set to 19c, any higher than that gets far too warm for me, but when I get a case of the cold knees I move it up to 20c for a few minutes to warm up.

It seems that you can direct the air down really effectively (must be the aerofoils shape of the dash) and give yourself really cold legs! Even with the air directed fully up there is still a bit heading down. A flap (aileron ) seems to do the trick. On the screen side the air hits the screen and gets pushed down but that does not seem as bad.

My vents are always directed fully upwards with fans on high (I don't like air in my face in the car unless it's very hot outside). I don't have any perceptable air coming towards my legs, though I'm sure there's some given the design of the dash.

 

[Cnixon]

I have posted this here somewhere but now lost the thread!!
It has been noted that you can get fingers in passenger side vent (rhd) but not drivers side. At service centre I sat in several heat-pump Y/3's all the same having smaller vent height on drivers side - and air could not be directed up. Cars with no heat pump seemed to have the same gap both sides. Tech said he had not noticed this before. My solution is to insert spacers to make height the same both sides. I believe the larger x-section slows the air flow and prevents the Coandă effect being as strong so the vertical bleed can do its job and deflect the air up.

 

[thax1]

I have posted this here somewhere but now lost the thread!!
It has been noted that you can get fingers in passenger side vent (rhd) but not drivers side. At service centre I sat in several heat-pump Y/3's all the same having smaller vent height on drivers side - and air could not be directed up. Cars with no heat pump seemed to have the same gap both sides. Tech said he had not noticed this before. My solution is to insert spacers to make height the same both sides. I believe the larger x-section slows the air flow and prevents the Coandă effect being as strong so the vertical bleed can do its job and deflect the air up.

Can’t add to your solution, but double-kudos for working the phrase ‘Coandă effect’ into a Sunday evening.

 

[Cnixon]

Had to go on Wikip for that speeling. It was either that or Bernoulli principle. It all hot air to me...or cold air mostly hitting my knees.

 

[Cnixon]

Ok this is not getting better with the cold weather, the Coandă spacers working a treat by the way, but I believe we have something else at play. Even with the vehicle up to temperature there is a really cold draft by my (rhd) right knee. It also feels (wet finger test) to be cold air being drawn into the gap between the door and end panel of dash and obviously across my knee. Other posters have highlighted cold drafts at bottom of doors due to poor seals not touching frame!!. So here is my idea. This is air being drawn into hvac for recirculation, there is always some it is not 100% fresh air usually 10%. Turning off hvac seems to stop this draft. Placing a small microfibre towel over my jeans knee fixes the problem within seconds. My model 3 seals became detached and sagged within a few days at the bottom but the Y never had this problem (I was ready for it). I suspect it might be the cold rear area which is unheated when seats not occupied being dragged forward? Any one else similarly afflicted?