A/C comes on when sitting in the car with everything turned off

[johnny_cakes]

I'm a new owner of a 2019 Model 3 and I encountered a strange A/C behavior yesterday. My wife was driving and I was in the passenger seat. She parked the car and went into a business meeting while I worked on my laptop in the passenger seat. Outside temperature was 9C (48F) while cabin temperature was a comfortable 20C (68F). Everything was turned off in the car, including climate control. I knew the cabin would slowly cool down, but my wife's meeting was only 1 hour so I was fine with that. After about 5 minutes of being parked, the A/C suspiciously started blowing cold air into the cabin. I looked at the Tesla app on my phone and it showed no indication of climate control activity. I turned climate control on then off from my phone to get the A/C to stop. Then after several minutes it happened again, at which point I had to turn climate control back on then off to get A/C to stop. I had to do this over and over again. It was extremely frustrating and cabin temperature was getting unnecessarily cold (down to 13C (55F) after 8 or so cycles of this. Anyone know what was happening and what I can do to prevent it?

 

[GtiMart]

I believe this is normal. Once you have used the AC and get out of the car, it will automatically run the fan to dry the AC radiator. This is to prevent mildew which eventually causes bad odors. By cycling the AC you turned that off, but since you stopped everything again the car decided to do it a few minutes later.
I believe that if you had tapped the screen to tell the car to stay on, it wouldn't have happened. In fact, since you're there, you can turn on the HVAC and leave it to a comfortable temperature. Contrary to an ICE car, leaving the HVAC on doesn't pollute

 

[johnny_cakes]

Thanks for the reply @GtiMart! That makes sense.

 

[Teslinator]

I am having a similar problem with my 2018 model 3 performance. I am the original owner of this vehicle and the problem with the a/c only just recently started happening.

The a/c has been randomly coming on after I turn the car off and go inside my house. And no, it is not the fan trying to cool down the battery. The A/C system is coming on and cooling down the interior of the car to whatever temperature the climate control is set to for the interior of the car. I have never previously experienced this problem with the car for the last 5 years I have owned it. I am doing nothing different with the operation of the car since I owned it. I have tried doing a reset on the car computer a couple of times but it has not fixed the problem. I am suspecting that it the result of some update or my computer system is somehow now compromised.

I have also have one other weird thing happening. I quite often have find my headlights to my car to still on hours after parking it and coming out back into my garage. The car is in park and locked. This likewise is a new event that recently started happening

Anyone else experiencing this problem or a similar problem and have a solution?

 

[Watts_Up]

I believe this is normal. Once you have used the AC and get out of the car, it will automatically run the fan to dry the AC radiator. This is to prevent mildew which eventually causes bad odors. By cycling the AC you turned that off, but since you stopped everything again the car decided to do it a few minutes later.
I believe that if you had tapped the screen to tell the car to stay on, it wouldn't have happened. In fact, since you're there, you can turn on the HVAC and leave it to a comfortable temperature. Contrary to an ICE car, leaving the HVAC on doesn't pollute

This was described in the videos referenced in this TMC thread:

This design flaw makes Tesla’s Model 3 smell bad!

Interesting video content: This design flaw makes Tesla’s Model 3 smell bad! (Part 2) Here is also the first video: This design flaw makes Tesla’s Model 3 smell bad! (with fixes!)

teslamotorsclub.com

 

[Teslinator]

I do not believe this situation is the fan turning on to dry out the AC radiator. If I last had the AC set to low, when the AC randomly turns on, it operates at the last setting. In the instance where I have it set to low, it will cool the interior of the car down to the high 50s. The AC is actually operating, not just running the fan.

 

[parsec]

Contrary to an ICE car, leaving the HVAC on doesn't pollute

Only if your electricity comes from a pollution free source, which does not yet exist. If I set my cabin overheat protection to "On" my battery is more quickly drained. Keeping the car at a comfortable temperature while I am not in it uses even more battery charge.

 

[Jangy]

Why would you try to turn it off in the APP instead of on the touchscreen? It won't turn on if you turn it off on the touchscreen, even if you drive. The rest of the noise in this thread should be taken with lots of salt. The car NEVER runs the HVAC for any purpose except creature comfort. The extra battery management noise is not from running the air in the car.

 

[stopcrazypp]

Why would you try to turn it off in the APP instead of on the touchscreen? It won't turn on if you turn it off on the touchscreen, even if you drive. The rest of the noise in this thread should be taken with lots of salt. The car NEVER runs the HVAC for any purpose except creature comfort. The extra battery management noise is not from running the air in the car.

Not exactly. The car does run the fan automatically to dry out the evaporator even with AC turned off. It was added in an update a long while back to address long running complaints about a moldy smell from the car.
Edit found the reference to when it was added 2019.12.1.2:

Humming noise while parked in garage

Twice in the past week I’ve entered my garage and been greeted by my 3 making a noticeable humming noise. Tonight I was able to reach in throuh the drivers window (which I had left open) and I could feel air blowing down in the footwell. My initial thought was that I accidentally switched...

teslamotorsclub.com

It is mentioned here in the manual under Climate Control Operating Tips:

• You may hear the sound of the climate system inside the cabin of Model Y when Parked. It makes a low fan noise. The climate system attempts to dry itself out to minimize additional moisture or musty odors. This is a normal operation and not a cause for concern.

https://www.tesla.com/ownersmanual/model3/en_us/GUID-4F3599A1-20D9-4A49-B4A0-5261F957C096.html
Heat pump(?) continues to run until a door is opened and closed?

 

[Jangy]

Not exactly. The car does run the fan automatically to dry out the evaporator even with AC turned off. It was added in an update a long while back to address long running complaints about a moldy smell from the car.
Edit found the reference to when it was added 2019.12.1.2:

Humming noise while parked in garage

Twice in the past week I’ve entered my garage and been greeted by my 3 making a noticeable humming noise. Tonight I was able to reach in throuh the drivers window (which I had left open) and I could feel air blowing down in the footwell. My initial thought was that I accidentally switched...

teslamotorsclub.com

It is mentioned here in the manual under Climate Control Operating Tips:

• You may hear the sound of the climate system inside the cabin of Model Y when Parked. It makes a low fan noise. The climate system attempts to dry itself out to minimize additional moisture or musty odors. This is a normal operation and not a cause for concern.

https://www.tesla.com/ownersmanual/model3/en_us/GUID-4F3599A1-20D9-4A49-B4A0-5261F957C096.html
Heat pump(?) continues to run until a door is opened and closed?

That isn't what is turning the system ON when OP is sitting in the car. You are just adding noise for no reason. Running the fan is not the same as running the AIR IN THE CAR. And it isn't the same as the unit coming on in the touchscreen. If the driver left the system ON and the car detects someone in the seat, then the system will turn on. In addition, there is no way to override the activity that the car does on its own. You can't jump on the app and turn it off or even see that it is going. OP specifically stated that he kept turning it off in the app and it kept coming back on. Let's stay on point here, instead of just going after random facts

 

[parsec]

That isn't what is turning the system ON when OP is sitting in the car. You are just adding noise for no reason.

"It's not noise. " And it is not for "no reason". You wrote "The car NEVER runs the HVAC for any purpose except creature comfort. " That's untrue. Stopcrazypp was correcting your slip-up for the benefit of others here who might like to know how the system actually works.

 

[stopcrazypp]

"It's not noise. " And it is not for "no reason". You wrote "The car NEVER runs the HVAC for any purpose except creature comfort. " That's untrue. Stopcrazypp was correcting your slip-up for the benefit of others here who might like to know how the system actually works.

Thanks. That's exactly the reason I responded. Too many people are unware this feature exists and then when the fan turns on by itself seemingly for no reason, they think the car is broken or has a problem. I just wanted to put the reference out there.

I should also note there is nuance in the OP's post. The OP was sitting the passenger seat, not the driver's seat. When you sit in the passenger seat, the behavior is different. The screen will actually turn off. If you wait long enough the car goes to sleep too (you hear the contactor clunk). To interrupt this, you can put some weight on the driver seat sensor and the screen will turn back on. As such, I can totally see the car triggering that fan mode in OP's situation, depending on how long he was sitting there. The OP may not necessarily be experiencing the AC still on either. Outside air was 48F (while cabin temp was 68F and dropped to 55F after a few cycles of this), so if the fan was running with AC off, the air would still be cold in such a situation.

 

[MOE J]

I say it’s Tesla testing out their new climate controls for cabin via the latest update.