AC and air circulation option.

AC and air circulation option.

I always have to manually turn ON the RECIRCULATION option when I turn my AC on. Shouldn't the recirculation be on automatically every time I turn on the AC? Is this something that can be suggested to Tesla to get it in a firmware fix?

Magic 8 Ball | April 19, 2019

You can suggest anything you want to TESLA and it probably can be done with a firmware update.

gmr6415 | April 19, 2019

Generally speaking automotive AC systems need at least periodic outside air flowing through the car to keep the ducts dried out. Particularly in humid climates constantly running on recirculate can end up allowing mold to grow in the ducts, and it can get pretty stinky or old smelling. Fresh ionized air is a good thing flowing through your car.

I would think they default to outside air in order to help mitigate that issue. If you constantly run on recirculate, Tesla defaults to outside air, and you get mold growing in your ducts, it's your problem.

M3phan | April 19, 2019

@gmr6415, never heard that constant recirc creates mold or stink. Everything I’ve heard and read (and re checked just now online) says no problem with leaving recirc on. Only time it helps to disengage is in cold weather to help avoid fogging windows. Genuinely asking: How does recirc create mold?

gmr6415 | April 20, 2019

@M3phan, First off AC works as a dehydrator, so AC systems themselves dry the air which is why you find a puddle under your car after driving with the AC on and parking it for a while. When it's humid outside the AC can only do so much and moisture builds up in your car in anything that can absorb it. As time goes on that moisture trapped in your seats, dash, headliner, carpets, etc is never dried out completely and the relative humidity in the air in your car can become greater than outside air. As a result you end up circulating moist air through all of your ducts all the time. When the car sits your duct work can start growing mold spores as well as your seats and everything else. It's so minimal you can't see it on surfaces. Because of the twists and curves of most vehicle duct work there are places condensation can puddle which makes it the most likely place to grow spores. Molds love heat and you know as well as I do cars sitting outside get a lot hotter than most any building. Mold spored feed on dust, dander, skin cells, etc. Your car is the perfect habitat to grow mold.

I'll be the first to admit I don't know exactly how Tesla's fresh air vs recirculate is designed, but in general vehicles when on fresh air open up vents to allow fresh air in and others to let fresh air out; therefore, constantly flushing fresh ionized air through your vehicle. Ionization is mother nature's natural anti-bacterial, anti-fungal and anti-viral. It helps decontaminate everything it touches. Additionally even when it's humid outside because of moisture build up inside your car the outside air can be dryer than the air in your car, so as it flows through the car it can pick up moisture and remove it from your car. Just as using a towel after a shower wet goes to dry.

I was a mechanic for almost 25 years. We ran into mold growth in duct work with tractor trailers and motor homes all the time. Additionally I now live in FL. House AC systems constantly recirculate the same air except for what is brought in when opening doors and windows. There is no fresh air option with home AC systems. Removing mold from air ducts is an industry of it's own in FL.

If you live in a dry area it probably isn't as much of a problem. Fresh ionized air is good for your car's duct work, everything else in your car and you.

The following is on mold build up in HVAC duct work in buildings, but keep in mind your car is an even better environment for growing mold than most any building.

What causes mold infestation in the HVAC air ducts?

A warm location with high water vapor content is particularly prone to mold buildup within the ducts. Water vapor can form within the duct system when cold air passes through, and when there is high water vapor content in the outside environment, the water droplets usually collect instead of evaporating. It forms the most conducive environment for mold growth. The nutrition for the mold usually comes from dust, dirt, dead skin cells, pollen, and animal dander that collects over months inside the duct along with the water.

russr1123 | April 20, 2019

It’s weird because when I turn on auto, it almost always has the recirculate button on. Having been in a car in the past where I used it almost exclusively, I can tell you that the mold does build up and start stinking. So now I want to make sure it isn’t using it a lot, but it seems to be. Maybe it is based on the moisture in the air outside? Not sure how it decides when to turn it on or off.

M3phan | April 20, 2019

Asked, answered! Thank you.

Daryl | April 20, 2019

When I come back to a hot car that has been sitting out in the sun, I always turn off recirculate for a few minutes because the outside air is cooler and cleaner than the inside air. Hot plastics outgas noxious chemicals.
However, being able to precondition the car remotely I think this is less of an issue.

EVRider | April 20, 2019

Doesn’t the car automatically adjust the recirculation if you use Auto mode? I would assume so.