AC Diagnostic Help

[Dublin 'Eer]

I’ve been having some issues with my AC and wanted to see if anyone else has had a similar experience and how it was resolved.

On my 2016 S, the AC is very cold (high 30s or 40s) most of the time; however, sometimes when the outside temperature gets into the upper 80s and 90s, the AC blows air in the 60s and 70s. I’ve also noticed times when the supercharging speeds drop dramatically, and the same issue happens with the AC blows warm air.

It seems to me that the system isn’t generating enough power to both cool the battery and also provide cool air for the AC. I haven’t received any low coolant level warnings. Any assistance is greatly appreciated. B

 

[vcor]

You didn't state what version/year of your car. I assume it's prior to the 2021-2022 LR/Plaid?

Yep, that happens sometimes. There are two separate issues with older cars. First, the condenser can freeze up which then generates very little cooling. Once it thaws out, you get cooling again.

The second issue is Supercharging on a hot day, the cooling is diverted to the battery, which gets priority. The act of Supercharging at high currents heats up the battery, and the choice would be to lower the charging rate (which most owners do not want) or pump more cooling to the battery. It can't be allowed to exceed a certain temperature or the battery will be damaged. Tesla elected to give priority to cooling the battery over the cabin.

The new LR/Plaid does not seem to have these issues, as it uses an entirely new HVAC system with a heat pump. It appears to be far more powerful than older models.

 

[Dublin 'Eer]

You didn't state what version/year of your car. I assume it's prior to the 2021-2022 LR/Plaid?

Yep, that happens sometimes. There are two separate issues with older cars. First, the condenser can freeze up which then generates very little cooling. Once it thaws out, you get cooling again.

The second issue is Supercharging on a hot day, the cooling is diverted to the battery, which gets priority. The act of Supercharging at high currents heats up the battery, and the choice would be to lower the charging rate (which most owners do not want) or pump more cooling to the battery. It can't be allowed to exceed a certain temperature or the battery will be damaged. Tesla elected to give priority to cooling the battery over the cabin.

The new LR/Plaid does not seem to have these issues, as it uses an entirely new HVAC system with a heat pump. It appears to be far more powerful than older models.

Thanks for the response. It is a 2016 Model S with a 75 kW battery. I am the original owner, and it has about 121,000 miles on it. This is a new behavior which makes me wonder if the AC unit is going bad.

 

[ucmndd]

FWIW, my high mileage (146k) 2016 S75 does exactly the same thing and has done it more frequently lately. If you look closely when it's happening you'll likely catch the little exclamation point icon at the top of your MCU screen and an active alert that says "Cabin AC reduced, vehicle systems cooling".

I recently had the AC serviced and desiccant bag replaced to see if it was something simple, but the compressor itself seems fine and can blow ice cold air when it wants to, so I've come to accept it's probably functioning exactly the way Tesla is telling it to. My primary suspects:

* Recent firmware updates telling the car to be more aggressive with battery cooling
* High mileage battery cells with increased internal resistance, therefore more heat, therefore needing more active cooling
* All of the above