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HVAC Control - for those over 50

rjpjnk

Active Member
Mar 12, 2021
1,010
621
NJ
Please describe the circumstances under which your car turns on the heat (blows hot air) in the summer.
It happens under various circumstances, but one that I notice frequently is when the cabin temperature is very close to the target temperature set. As the AC reaches the set point and the system no longer needs to reduce temperature but just to maintain temperature it seems to sometimes over react and puts out heated air instead of just recirculating the existing air without additional cooling.
 

DarthStar

MYP MSM Tow
Supporting Member
Jul 7, 2021
194
288
SoCal
It happens under various circumstances, but one that I notice frequently is when the cabin temperature is very close to the target temperature set. As the AC reaches the set point and the system no longer needs to reduce temperature but just to maintain temperature it seems to sometimes over react and puts out heated air instead of just recirculating the existing air without additional cooling.
My MYP does this exact same thing: SW 2021.11.102.
 
In Cali, we often have cool mornings with hot afternoons into the evening. For my early morning drives, it is often around 60 degrees out. This is warm enough for me, but with the "AC" temp set to 68-70 from the day before, the heater kicks in making it uncomfortable and wasting energy. So I turn down the temp. Then later in the day I get in, and the AC is *blasting* trying to get down to the 60-64 I set it to in the am, so I turn up again to 70. It's a constant dance and annoyance.

FWIW, I previously had a honda accord from around 2006 that had *much* more intelligent auto AC that rarely if ever made it uncomfortable.
 

rjpjnk

Active Member
Mar 12, 2021
1,010
621
NJ
I hear you. It is such a hassle. The Tesla system could probably be fixed with a software change if they ever take it seriously. They have so many different temp and humidity sensors it is a shame to see them mess up so bad.
 

rjpjnk

Active Member
Mar 12, 2021
1,010
621
NJ
Same here, and this is my primary complaint. The car can make plenty of cold air, and it can make plenty of hot air. The problem is that it cannot regulate the temperature well. I have measured at least 10 degrees fluctuation for a single set point of 74F. I am hesitant to go back to the SC because they merely run a diagnostic and declare it to be "performing as expected"

I doubt this is typical or there would be many people complaining. One day 68F is barely cool enough, and then the next day 76F is freezing cold. It really seems like the car just is not able to measure the cabin temperature correctly.
 
I fully agree with the OP. In winter, I want to set the temp to 20 C (68F) to warm me up a bit, but if the car is sitting in the sun, and the temp gets up to 25, I don't want to jump in to a toasty warm car and have the air con blow cold air at me! In summer, I'm happy to cool down to 25 C (77F). Where I live, we often have cold days and warm days interspersed, and it's common on a cold day to have the car warm up while parked in the sun. It's not a matter of changing the temperature once in autumn (fall) and once in spring. I'd love to be able to set a comfort range for use all year round.
 
One day 68F is barely cool enough, and then the next day 76F is freezing cold. It really seems like the car just is not able to measure the cabin temperature correctly.

That could be due to a sensor problem. If it's been happening only since your last software update, I'd ask the service center to push an update or re-push the release you have in order to reprogram the sensor controllers. That fixed climate control problems for a bunch of owners that started with a windshield replacement (which includes the sensor electronics in the rear view mirror).
 
So what's being asked isn't something available on any car, or at least I'm 99.9% certain no vehicle has climate control, manual or otherwise, that allows you to select a temperature range. It's either manual and you're constantly adjusting the temp to reach the comfort level you desire, or it's automatic and you choose the cabin temperature you want. It' sounds like maybe what you should do is set the cabin temp to be lower than the exterior ambient temp and then turn off the A/C. That will prevent the car from heating or cooling the cabin, no?
 
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rjpjnk

Active Member
Mar 12, 2021
1,010
621
NJ
I didn't get the impression anyone was asking for a range of temperatures, but perhaps I misunderstood surfdabbler's request?

I personally would be happy if the car could maintain a constant set temperature, but I realize that is a difficult task given the sudden heat load changes from windows and such typical of automobile environments. I think a fluctuation (hysteresis) of +-1 deg F about this point would be excellent. Even +-2 would be good. But my temp swing is much greater than this. I'm seeing more that a 10 deg F swing.

I heard the new SW 2021.36.5 has some changes to address cabin comfort. I am updating to this version tonight. Maybe it will help. :)
 
Last edited:
I didn't get the impression anyone was asking for a range of temperatures, but perhaps I misunderstood surfdabbler's request?

Some of us DO want to set a temperature range.

E.g. when driving through a hot valley, cool me just to a comfortable temp but don't start heating me to that temp when the outside cools down. Ditto in reverse when driving up into a cool mountain pass and back.

(Leave aside the need to dehumidify sometimes.)
 
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Automotive HVAC has more design challenges than your average home, most notably humidity control. For example, when the temp is cool but humid, you have to heat and cool simultaneously to dry out the air and prevent windshield fogging without also freezing the occupants. The car has a temp and humidity sensor in the rear view mirror housing that determines how much dehumidification is needed.

Yes, your proposed basic thermostat settings would save energy, but at the expense of occupant comfort and visibility in humid conditions.

Don’t get me wrong - Tesla’s programming isn’t perfect. Just cautioning against oversimplification.
In Auto mode does the car automatically try to avoid the window fogging (e.g. if it starts raining)?
 

rjpjnk

Active Member
Mar 12, 2021
1,010
621
NJ
I am happy to report that SW 2021.36.5 seems to have fixed mr climate control issues. For 3 days now it has worked very well. Hopefully this will continue. Well done Tesla.
Well, guess I spoke too soon. Climate control seems back to its previous poor performance again ever since I updated to 2021.36 5.5 a few days ago. Not sure if it has anything to do with the content of the recent update but it sure seemed good for a couple weeks between updates.

I guess Tesla is messing with the climate control in these pasts couple updates. I hope they get it fixed soon. At least it’s getting attention.
 
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