The Straight Shift with The Car Chick

Stay Cool and Save Money: Your Summer Guide to Car A/C Systems

• LeeAnn Shattuck, The Car Chick: Your Car Buying and Repair Expert • Season 2 • Episode 112

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Summary

In this episode of The Straight Shift, The Car Chick® dives into the world of car air conditioning, debunking common myths and explaining the science behind how A/C systems work. From the importance of maintenance to understanding the components of the A/C system, listeners gain valuable insights into keeping their vehicles cool during the summer months. The Car Chick® emphasizes the significance of proper care and maintenance, including checking the cabin air filter and understanding the closed-loop system of refrigerant. The episode concludes with practical tips for maintaining A/C efficiency and comfort while driving.

Takeaways

  • A/C systems pull heat out of the air, not blow cold air.
  • Refrigerant is a closed-loop system and doesn't get used up.
  • Using the recirculate button is more efficient in heat.
  • Starting a car with A/C on doesn't harm the battery in modern cars.
  • Using A/C in electric vehicles is efficient and safe for pets.
  • Regularly changing the cabin air filter is key to A/C performance.


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Copyright ©2024 Women’s Automotive Solutions Inc., dba The Car Chick. All rights reserved.

LeeAnn Shattuck (00:00)
Hey everyone, and welcome back to The Straight Shift, the podcast that cuts through all the automotive bull and helps you drive smarter. Let me tell you what inspired today's episode. Just a few weeks ago, the air conditioning in my house died. Right in the middle of that lovely little heat dome that was baking the Southeast like a convection oven. Temperatures soared into the upper 90s, even hit a hundred a few days, and the humidity was thicker than a milkshake.

My ancient 25 year old air conditioning system just gave up. Thankfully, it only needed a new compressor motor and not a full replacement. So I escaped with a $700 repair instead of a $10,000 repair. Yay for small victories. Now granted, my house A/C units are 25 years old, so I can't exactly pull out my shocked face for this, but I found myself just going out to sit in my car to cool off.

And that got me thinking, we all depend on our cars A/C to survive summer driving, but most people don't know how it actually works or how to take care of it or what not to do. So today we're going to bust some common myths about car air conditioning that could leave you sweaty, frustrated, and even broke if you fall for them. So let's chill out and talk A/C.

Before we get into roasting some myths, let's talk for a minute about what's really going on behind your dash when you press that magical A/C button. This will involve getting a little bit nerdy and going over some basic physics, but I promise you will not need a PhD to understand it. Despite what it feels like, your car's A/C doesn't just magically blow cold air into the car's cabin. It's actually pulling heat out of the air

inside your car. It's kind of a high-tech game of hot potato powered by some seriously kick-ass physics. The A/C system is a closed loop system based on the principles of thermodynamics and fluid mechanics, and it uses a special refrigerant fluid to move the heat around. All right, I told you we were going to get nerdy here. So for those of you who didn't take or just don't remember that school physics

Thermodynamics is the study of how heat and energy move and change form. Basically, it's the study of how hot things become cold and cold things become hot because everything likes an equilibrium. Fluid mechanics is the study of how fluids move and behave. A fluid is defined as any substance that can flow and takes the shape of its container. So fluids are things like liquids, gases, and cats. Yeah, cats are fluids.

They're not part of your A/C system, but they're definitely fluids. And if you want to see some examples of that, just check out any of my social media pages.

Now let's talk about the main components of your car's A/C system and how they work together to keep your butt nice and cool. The compressor, this is the MVP of the entire system. It's typically mounted to the front of the engine block or somewhere in that vicinity and is powered by a belt that connects it to the crankshaft pulley. So what that does is when your engine is running and turning the crankshaft, that means it is also by way of this belt, powering the A/C system,

and also a variety of other systems in your car. But when you turn on the compressor, the compressor clutch engages. That's what tells the compressor to be on or off, so that your A/C is not on just naturally all the time when your engine is running. So when that clutch engages, the compressor turns on and it literally compresses the low pressure refrigerant gas into a high pressure, high temperature gas.

It's a lot like how the pistons in your car's engine compress the air fuel mixture. In fact, A/C compressors, they use cylinders and pistons just like an internal combustion engine. It essentially gets all that refrigerant hot and bothered so it's ready to release the heat. That hot gas then flows through a metal line into the condenser. All the parts in your A/C system are connected by narrow metal pipes that we call lines.

So once it gets into the condenser, that's the part that's located in front of your radiator, behind the front grill. That's also the part that collects all the dead bugs on a road trip, but that's a side gig. Its main function is to cool all that hot high pressure gas by running it through very, very thin metal tubes and fins that spreads it out and gives it a much larger surface area for heat transfer. This is the thermodynamic part.

Air passes over the gas, thanks to either your car's fan running or your car simply moving and air naturally flowing over it, or both. And that dissipates the heat, turning that gas into a cooler, but still high pressure liquid. That's the condensing part. The gas changes to a liquid because its temperature drops below its condensation point. I told you this was going to be a little bit of a nerdy physics lesson.

But it means it just literally starts to chill out.

That is the fluid mechanics and thermodynamics working together. The cold liquid then flows through a line into something called the receiver dryer. This is a little water bottle looking part that filters out any remaining gas and makes sure that the refrigerant is a pure liquid that goes into the next step.

It's kind of like the Brita filter that you might use on your sink. But instead of filtering out debris and chemicals, it's filtering out moisture and gas. So I guess that technically makes it a fart filter. So this is why they don't let me name car parts, because this is what my brain comes up with. So now that your refrigerant is totally fart free, it flows through yet another line into a part called the expansion valve. This is where the refrigerant hits the brakes.

It's been high pressure and suddenly it hits this expansion valve and a valve's purpose is to control flow. So it encounters this sudden drop in pressure and that causes the temperature to further plummet and the refrigerant to partially evaporate. And it comes out as this cold mist. It's a part liquid, part vapor. And now it is ready to do its job of cooling your butt off. This is where it enters the evaporator.

The evaporator coil is inside the HVAC unit that is behind your dashboard. It's typically made of aluminum or copper and the cold refrigerant flows through the evaporator coils, making these coils which, similar to the condenser, have lot of fins and it makes it very, very cold. Then the blower fan, which is also mounted back there, it's drawing the warm air from your cabin

over those cold, cold coils. The refrigerant absorbs the heat from the air, cooling the air down. So it wasn't just blowing the cold air into the cabin, it was pulling in the warm air and sucking the heat out of the warm air. Again, thermodynamics. It's just, it's really cool physics. I'm sorry, I'm a little bit of a nerd, but it's very cool physics. And so now that air that has had the heat removed from it, it's nice and chilly,

it's pushed by the blower motor through the vents and into your face and onto your feet. Wherever you have it aimed. It is a truly glorious feeling. the evaporator also pulls moisture out of the air. So it is a dehumidifier. This is why your A/C helps defog your windshield. The humidity in the air condenses on those cold coils,

and it drains out of the vehicle through a small pipe. That's why you might notice a little puddle of water under your car after you've had the A/C running for a while. Totally normal, just your A/C system peeing. Natural function, don't worry about it. Then after the refrigerant's done its job in the evaporator, it exits as a low pressure gas again and returns to that compressor starting the whole cycle over again. So it is a closed

system. That same refrigerant just keeps going around and around and around like a roller coaster that never ends, heating up, cooling down, changing from a gas to a liquid to a gas again, over and over. So again, it keeps you cool by removing the heat, not by manufacturing cold. It's all about efficient heat exchange. Yay, thermodynamics!

Bet you didn't know that physics could be so much fun. Willing to bet it would have been so interesting in high school if they had taught it more practically. And I was lucky because my physics professor actually did. He was very cool. Mr. Bromley was one of my classmates' fathers and a football coach, and he did believe in practical physics. So we learned all about gravity and acceleration by dropping things off the roof of the school. And we learned about centrifugal force and centripetal force by

literally going outside in the winter and skating and, because I was a figure skater, having me demonstrate pulling in on a spin and getting faster and faster. We had a lot of fun, but we didn't talk about air conditioning, but cars A/C systems weren't as strong back then. And my old car didn't even have one. So I'm sure physics is more interesting today, but I hope you can appreciate it a little bit more the next time you hit that magical A/C button.

So what about that little recirculation button? That's the one with the little looping arrow that kind of looks like there's a treadmill inside a car. That's the recirculate button. When that is off, the system is pulling fresh air from outside the vehicle. And that's very helpful if your cabin is stuffy or the windows are fogged up. It'll help defrost it faster,

defog it faster. It's not so helpful if you're driving by a skunk or if you have sweaty kids and gym bags in the car. When that's on, the system just recirculates the air that's already inside the cabin. It makes the air circulation a closed system. It's way more efficient when it's hot outside because it's easier for the A/C system to remove heat from the cabin air

that is already cooler or starting to cool down than it is to constantly pull in that hundred degree swamp air from outside and try to remove the heat from that. So use that recirculate button on really hot days, as long as you don't have sweaty things in the car. You also want to pay attention to your car's cabin air filter. It's not just for filtering out all the pollen in the spring, although it does a good job of that.

Cabin air filter is usually behind the glove box and it filters the air coming through that HVAC system. If that cabin air filter is clogged with dust and pollen and whatever, then the air is not flowing as well through the system. So if your A/C feels like

it's not blowing as hard if it's not blowing as cold, or maybe it smells like old gym socks or musty or a little bit moldy. The first thing you check is the cabin air filter. Chances are it probably needs to be replaced. I realize that this is a part of what dealers are supposed to normally do with the very regular service. Like every year you're supposed to do this sometimes twice a year, depending on where you live. However, I have seen cases where

they've actually not done it. They've charged you for it, but they didn't actually do it. Whether they forgot or it was just intentional, I don't know. But always check that first if you feel that your A/C is not working as efficiently. Same thing in your house. The very first thing the repair guys looked at when they came over was they looked at my air filters and they weren't too bad. But he said, that's always the thing to check first and change those more frequently in the spring and summer. So I will be doing that religiously,

every 30 days, but my compressor motor just died because it was old enough to drink. This is how the A/C systems work in gas powered cars. So for my clients and friends out there who drive purely electric vehicles, how does that work? Well, in gas powered cars, as I said, the A/C compressor runs by a belt connected to the crankshaft pulley connected to the engine of the car. In electric vehicles, it's a little different.

The compressor is powered by an electric motor and that's connected to the car's high voltage battery. That means there's fewer moving parts. It's a lot quieter to operate, and it's typically more efficient, but the rest of the system works the same way. Same components, same process, same refrigerant. You're just not relying on the engine to run the A/C. This can be helpful in a couple of situations.

It's easier to run the A/C when the car is not on, it's not moving. Tesla calls this camping mode. That's why it's okay to leave a pet in the car for a short period of time if the A/C is running. And in an electric vehicle, if it has this mode, you can do that. If you were to do that in a gas powered car, you would have to leave the engine running and the key in it,

in order for the car's A/C to run and your pet to be safe in the car. This is why most people do not do that. So don't leave your pets in the car in the summer, even for a few minutes. I have used that technique at the racetrack because I will bring the minivan and put a mattress pad in the back of it and use it as a camper at the racetrack. And I will just leave the engine running all night with the hood open to help it keep itself

cool, the fans running, and I will blow cool A/C into the cabin so that I can actually sleep on race weekends in between my driving shifts. It's wonderful. And it doesn't actually use that much gas. I was a little worried about it, but I'll use less than a quarter of a tank throughout the whole night running the A/C with the engine running in that minivan. Totally worth a quarter of a tank of gas to not be sweltering hot throughout the night.

Now that you know how your A/C works, let's start busting some myths. I love myth busting. That was a great show. Myth number one, running your A/C kills your fuel economy. It reduces it, but it doesn't kill it. Not like you think and not in modern cars anyway.

Does the A/C load the engine and burn a little extra fuel? Absolutely. But we're talking about a few percentage points. It doesn't just cut your fuel economy in half or anything so drastic. Certainly not enough to justify sweating your ass off in the name of saving a little bit of gas. Just turn your A/C on when it's hot, people. It's totally worth it. And you're not using that much. Like I said, I went through less than a quarter of a tank running the car all night on idle with the A/C running at the track.

And that's just an old Dodge Caravan. It's like not even a super efficient new vehicle. Now running the A/C does suck some of the power and reduces a little bit of your umph. So if you got the A/C cranked and you're trying to get on it and merge onto the freeway, you might feel a little drop in power depending on your car. But again, it's not that bad. And I am willing to sacrifice a little bit of umph to stay nice and cool and comfortable.

In modern cars, it has less of an impact on your fuel economy than driving with the windows down at high speeds, which messes up your aerodynamics. And that has more of effect on your fuel economy than just running the A/C. If you're going through stop and go traffic, just crawling along and it's not hot as fuck outside. Sure, crack a window, roll them down, enjoy the breeze. But on the highway, roll up the windows,

turn on that A/C. Your fuel economy, and probably your deodorant will actually thank you for it.

Myth number two, you need to top off your refrigerant every summer. Nooo! Refrigerant doesn't get used up. It's not like windshield wiper fluid or gasoline. Remember, it's a closed loop system. So if your refrigerant is low, that means there is a leak somewhere in that system that is supposed to be closed. If your mechanic keeps selling you a recharge every summer, either they're BSing you,

or you do have a slight leak and they're just continuing to put a bandaid on a bullet hole for you. It means you're leaking refrigerant and that should really ideally be diagnosed and fixed. If it's very slight and you just don't have the cash to fix the whole system, I get it, but you are just kind of pouring money into it. Granted, I've been doing this on my house A/C systems for over 10 years, just limping them along because I don't want to have to replace them with a system that

definitely will not last another 25 years. But house systems are a little bit easier to do that with. With your car's system, at least get it diagnosed so you know how bad the leak is. Because one of these days, it's just gonna go. And it's better to be able to prepare for that than to have it happen in the middle of your family road trip down to the beach in the middle of summer.

Myth number three... blasting the A/C right away when you turn the car on damages the system. Nope, false. A/C doesn't care how fast you crank it. In fact, it often runs a little bit better when it's kicked in at full power.

That's because the compressor is designed to cycle on and off as needed anyway. The biggest thing is just to not hit maximum A/C if your car is an oven. The key is to roll the windows down for maybe 30 seconds. Go ahead, turn the blower on and blow some of that hot air out through the windows because if your car is hotter than the outside air, then you're just going to have to remove even more heat. So roll the windows down,

blast the blower for like 30 seconds, then turn the A/C on to max, roll those windows back up and let it do its thing. If you've got remote start and you got one of those fancy controllers where you can control your car from your smartphone, you can use a remote start, turn on the A/C. I don't know if they let you roll the windows down with a smartphone app. If you have a car that does that, definitely let me know in the comments, because that's actually a question I've never asked and that'd be cool.

But if you can get your A/C started before you even get in the car, you never have to experience that feeling of stepping into a convection oven. That would be so nice, especially for those of us with dark interior cars. Alright... myth number four... starting your car with the A/C running kills the battery. No, starting a car with the A/C on doesn't typically harm the battery or the alternator in newer vehicles.

Most modern cars are designed to automatically disable the A/C compressor during engine startup to reduce any load. The compressor is typically powered by the engine via a belt. It's not powered directly by the battery. Some of the accessories around it are battery driven. The blower motor, for example, that's one that does power from the battery, but that's a relatively small load compared to like the starter motor and a lot of the other accessories necessary to actually start your engine. So,

it's not a big deal in more modern cars. In older cars that weren't as efficient and didn't have the computers that were smart enough to turn things on and off, specifically to preserve battery life and preserve your alternator, newer cars are just a lot smarter than they used to be. And sometimes they're smarter than us. So let's enjoy that and let them do their job. So again, get in the car, have that A/C turned on, crank it up, especially if you have that cool remote start capability.

Myth number five. The A/C doesn't work when the car isn't moving. Well, that kind of depends. The condenser does need airflow in order to release heat. When your car is moving, air flows over it naturally. When you're sitting in traffic, that's when the cooling fan kicks in to do its job. If that cooling fan is not working, your A/C will not work as well at idle.

But if that cooling fan is bad, you got bigger problems because that cooling fan also helps keep the engine cool. So get it fixed ASAP. Your engine overheating and going bloowy is a lot worse than you overheating. All right, myth number six. Using recirculation mode is bad. Wrong. That's your best friend.

On hot days, use that little button to your heart's content. As I said, it cools the cabin faster and makes the system work less hard because the air inside the cabin is not as scorching hot as the air outside. Only turn it off if you got some funk inside the car and you need the fresh air. All right, finally, myth number seven... running the A/C in an electric vehicle totally kills your range.

Like fuel economy and gas powered cars, running the A/C will not destroy your range. It's not going to totally cut it in half unless you're already down to your last few electrons and you're desperately trying to get to a charger uphill in July. In that case, you might want to sweat it out. But in general, the A/C doesn't suck as many electrons as you might think. Studies have actually shown that moderately hot temperatures, which

they define as kind of between 80 and 90 degrees Fahrenheit. That loss range is only around three to 5%. So that's not too bad. Now, if you're in stupid hot weather, you know, 90 degrees above a hundred degrees, it can have more of an impact. You could see a drop of 15 to 20 % in your EV range. But when it's crazy hot out there anyway,

Like really, how far are you gonna go? You're just going out because you have to, you gotta run the store, you're get back home to the A/C as quickly as possible or get to work and get in the air A/C. Don't just drive around. But if you think about it, look at all the cars that had problems in the winter with their batteries. the heat and cold weather can drain the batteries just as much. In the winter, the batteries don't work as efficiently because of the cold. So you're gonna see actually a bigger drop in battery power

and EV range in the winter, then you are likely to experience in the summer, with just the A/C running. So go ahead, run the A/C, put the car in camp mode, definitely leave the A/C on if you've got a pet in the car while you run into the grocery store quickly. It's not that bad.

So there you have it folks. I hope this little lesson in physics has given you a better understanding of how your A/C system actually works in your car so that you can separate solid advice from a whole lot of sweaty nonsense. Taking care of your car's A/C is mostly about maintenance, not about these myths. Change your cabin air filter frequently and regularly. Don't ignore any weird smells or weak airflow because that means something's wrong. Start by checking the cabin air filter.

And if it stops cooling, don't just try to recharge it blindly. Get a proper diagnosis. Find out what is actually wrong. And be sure to clear off all the dead bugs when you get back from that road trip. And even check it periodically, because that road trip could just be a trip to the grocery store and a big old pretty butterfly decided, you know, to smash into your grill and it's sitting there nice and dead on your condenser blocking airflow. So when you wash your car,

be sure to get in there with the hose and make sure that that condenser is also nice and clean. Your comfort and your wallet will thank you. If your car's A/C just isn't cutting it and you think, well, you know, just maybe it's time to get a different ride because I don't want to spend a few thousand dollars to fix the air conditioner, you can either check out my online buying course at carbuyingcourse.com or you can check out my full perfect car package where I do all the work for you

on my website at thecarchick.com. Thanks for tuning into The Straight Shift. Remember to share these episodes with your friends, drive safely and stay cool my friends. I'm out of here.