How the AC and Heat Work in your Car
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- เผยแพร่เมื่อ 7 ก.พ. 2025
- In this video we take apart the heating and air condition unit to see what’s inside and how it works!
There are four main functions in your car’s heating and air conditioning system, including the air source (recirculate and fresh air), fan speed, temperature and vent mode. All of these happen behind the dashboard in the HVAC unit. These are a subset of the air conditioning system (including compressor, condenser, drier, expansion valve) and the heating circuit (engine, radiator, thermostat and water pump).
The heater A/C box in this video was from a 2006 Volkswagen Jetta. Main components include the recirculating flap and its motor, blower motor, blower motor resistor, air filter, housing, evaporator core, thermostatic expansion valve, heater core, electric heater, temperature control motor, mode selector gears and mechanisms as well as vent valves.
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It's amazing just how much engineering goes into literally everything and we never know anything about it, things 'just work'. Lots of smart people did a lot of thinking to make our lives so comfortable.
Agreed. We take this for granted yet use it everyday
There's no one in the world that can explain that so good and easy to understand. A little fast but no bullshitting. Straight to the point and explain in quite a bit of detail. Seriously he just taught a whole semester of classes in a few minutes
I'm glad you appreciate my video style, thanks
Engineering is an art… very few people are aware of these mechanisms that are in the background the work with the push of a button.. Very informative video ❤✨
That's very impressive! Someone, or a team had to design all those ducts and mechanisms to fit in a rather small space and not rattle around when driving!
To be fair, the design is very similar to the mk5 Jetta. So the design itself is at least from 2007. And was still being used up until the mk7 Jetta.
This is from a mk5 2006 Jetta tdi
Agreed!
Great job, respect to the people that designed this, you’d think they’d go wrong all the time with the amount of stuff packed in there.
Agreed! It's something we don't see or think of and it just works
Agreed! It's something we don't see or think of and it just works
After seeing this I fully understand how the AC system actually works!
The freon that heats up as it cools down air turns into gas and has to be turned back into a condensed liquid (cooler) and compressed to be used again. Really smart design!
It sure is an innovative design. If only they could make it more efficient
Some guys explain the practical and others the theory part.But you explained both with diagrams.Well done bro.❤
Mind blown to the level of engineering involved in here!
You've really mastered your craft. A pleasure to watch and be educated
You are the only one explained so so so clear and very detailed. I really appreciate of your video.
Very good and speedy explanation (as opposed to slow and boring) of the entire AC process and related equipment. Thank you so much! 5 Star review!!
Thanks..short and to the point is my style
You are legend 👍
I haven’t seen more complicated hvac on any car period
Hummm, this is a pretty basic setup, i don't see anything that could be removed without loosing core functionalities
No one can explain in a better way as you did. Simply Amazing!!!..Thanks a lot for the video.
Glad you liked it!
Bro you are amazing. Everything is well explained with one toothbrush.
this is very well done. I love the schematics to help visualize everything
Amazing videos. Thank you for doing this. Even though I knew the principle of how it works I never saw it disassembled. I hits me how cheap and prone to failure the components are. Crappy little hobby motors, plastic gears without a lick of grease - it's terrifying.
Thank you for showing us this!
You are welcome! It sure is interesting to understand the engineering that goes into making a car work on things like this that you often don't see or think of!
Watching from Al Khafji Saudi Arabia thank you for very informative Vlog
You are welcome from Canada
So well explained on such a complex , clever engineered system..
It sure is some interesting engineering behind something we take for granted
What an awesome video. I have a Mk5 Golf which has this unit so I’m amazed at what is under my dashboard.
Glad you enjoyed it. The HVAC system is quite a marvel that no one ever thinks about.
Your breakdown videos are hands down the best on TH-cam.
I would so much rather pull a transmission or an engine than pull a heater core...ugh....you got dedication bro!
There is simply NO other channel like this
Well I'm glad I'm here then 🙂
Great video , you should make more of them in in this style !
I have a lot of teardown videos like this. Suggestions are welcome
Super helpful ! Extraordinary detail !!
Thanks !!! 👊🏼
Glad you liked it!!
So since running the fan at a lower speed just means that there is extra electrical resistance added to the circuit, does it take just as much electricity to run the fan at full speed as it does to run it at low speed?
Yup. That's correct.
Newer cars use either pulse with modulated DC motors or brushless DC motors.
Never thought of that
No, it takes less electrical energy at the lower setting. As the total resistance of the circuit is higher, the current will be lower, therefore the total consumed power will be lower.
@@fritsified5952 The total resistance is higher due to the heating elements used as resistors. So, like and electric stove the energy is being used.Note that the elements are monted in the air duct to dissipate the heat.
The answer to this question has potentially upsetting implications for how I've lived my life. I regularly use lower fan speeds in my car and home so I don't use as much electricity. Have I suffered through hot nights when turning my bedroom fan higher would use no more electricity?
Really appreciate this video as I'm trying to figure out why the AC isn't as cold as it should be in my Honda Fit!
Very impressive as always!!!
Thanks
I wanted to understand this mechanism of cabin air, really thanks to you brother. Love ❤️
Excellent excellent excellent job
Thanks for the master class!
That is what VW calls a semiautomatic single zone HVAC system, in marketing terms is called Climatic. There is an even fancier system in which everything is automatic (air distrutibution) and has dual zone climate control with more temp sensors, electic acutators and fan speeds. It's esentially the same system, but with additional components which is called Climatronic.
On both systems, the interior temp sensor is an infrared sensor located in the middle of the climate control panel. In this video, you can see it between defrost, recirculation and ECON buttons.
Wow good to know. You can definitely tell where the climatronic would have been in the mould for the dual zone by having the passenger and driver flaps separate
The most brilliant explaininq I have ever seen and heard
Sure is interesting, especially the way each brand handles these same tasks.
Amazingly explained 🔥
Thank you for the information.
Imagine the manpower that went behind building that bad boy! 😮 just incredible
This explains everything, thank you 👍👍
Thank you speedkar99 your whole videos what I am watching since last 3 years are really educational. through those videos I could understand automotive engineering based on textbook knowledge Man you have nice day and Keep health, thank you again
Glad you like it and all the best on your automotive stuides
Thanks for your cool demonstration 👍
You are welcome
Excellent explanation as always like your other vids. Just replaced the resistor on my NZ based Tiida/Versa. I discovered that on an online manual, you can run simple manual diagnostics to display codes for the actuators and circuits and display temperatures for the heaters' input sensors. Probably heater diagnostics can be done for the Jetta.
Never knew they included an electric resistance heater in the HVAC system. Crazy!
so informative omg thank you so much
You're so welcome!
Thanks for the teardown
You are welcome
great teacher indeed, Regards
Amazing and wonderful video , thanks
Amazing work
Thanks. This was quite an involved
@@speedkar99 😀😂yes
brilliant explanation. Thank you
My old 70s chevy still has 5 crank air conditioning. Much less complicated. Great videos!!!
Thanks
this system is so complicated thanks
Wait until you see the automatic dual zone HVAC systems
My mom has a car that has a heater that would only work on certain settings and I may have figured out why! Thanks!
Great video, thanks so much. You helped me a lot
Another cool video. Just like this one.
r u psychic? this is exactly what i needed, my ac was making a noise yesterday. i think i can figure it out now.
Glad it helped
Great explanations as always :)
It amazes me how well he can explain the sequence of operations but has no idea that the condenser and evaporator are called COILS not cores. Gotta love engineers. Geniuses with no practical understanding
Always wondered where the "outside air" came from. 👍
Under the wiper cowl
I always wonder why, because it sucks in all the debris from the trees I use to park under. The blower comes before the filter, so maybe you get a rattle from a leaf. I have to throw out the filter every year. The motor filter is engineered better.
Great video and thank you.
0:50 Yes, After all These Years! Finally A Vent in Glovebox To Keep My Gloves Nice And Cool For those Hot Summer Months!.
The best HVAC systems in cars are the ones we’re all the blend doors are controlled by engine vacuum. Those never fail.
What about mechanical linkages?
@@speedkar99 yea but most the time the linkage breaks or comes off or gets out of alignment. Still anything better then having all the blend doors controlled by electric motors cause when they fail you gotta pull the whole dash out.
The T-7 ASE I failed today by 2 questions. Now I have to wait 30 days to retest. Good thing the A-7 is still a/c heater related so I’ll do “auto” first then retake the “truck” version after my 30 day cooldown period of failure
Great information
Awesome video
Thanks!
Alot more to this hvac system then my 2001 jeep grand cherokee hvac system. Same in a way but different
Such a complex system where many things can go wrong. My car has a slider for the temperature control and a slider for the fan speed. But buttons for the vent control. I never realized that everytime i press those buttons some servos or something moves those vents. The temperature slider is not hard to push, so I suspect that the temperature control is also electric.
Some heater cores from the cabin are gonna be a
pain to replace
All heater cores are a pain, but apparently on this Jetta it can be done without dash removal from the driver footwell
Great video Boss. I have a question. I had the same car jetta but its heater doesnot work. I have got my heater core replaced twice, thermostat changed, still when i start the car heater would work for 4-5 mins and then starts blowing cold air. Any suggestions on what could be the issue ….
The heater core is always recilculating coolant even when it's summer and HVAC system is off building up heat slowly at your cabin (some cars have electric heater core valve chocking the coolant flow)
Some companies designed to fix that, and the heater core is right in front of a firewall (aka super good insulation) that keeps heat from going behind the engine bay.
When we set the dial to the lowest blue or the digital temperature to the lowest setting, are we closing the path to the heater core or requesting the thermostat (temperature sensor) to read lower temperatures?
My doubt is. In heating mode, where does the air blown in the evaporator come from? Is it taken directly from the outside? Will that blow air have the same temperature as the air outside of the car before passing through the evaporator?
Awesome video 👌
Thanks
love your videos
Me too
So I understood but I need your confirmation, can I run both heater and AC at the same time and not harm anything?
When the evaporator core is being blown by the fan I hear it builds up moisture and there is some kind of drain pan for all of it, is this part of the HVAC system behind the dash?
Very informative. Thanks. I was actually looking. for a video on how the system differs between one for ICE cars and Battery Electric Vehicle (EV) where there are no hot liquid from the engine to regulate the air temperature out of the vents. Does EV use compressor rotation speed controllers to regulate air temperature instead?
Yes, check out my hybrid compressor video, it's all electric
Is it advisable or OK to set your AC temp to the lowest setting? Will there be changes to engine load or FC?
My question might not be related to this video, What is the torque of the cordless impact wrench that you use in engine teardown videos? I expect you to answer me, thanks a lot
It's an M18 1/2" miluakee impact wrench
So the air filter is after the fan? So it's not protected from dust and debri?
Hello, got any idea what might cause a burnt smell with the heating on, and also some additional noise even with the fan on the lowest setting? Audi A4 B9 TDI.
Sounds like you've got something stuck in the HVAc blower melting up
@@speedkar99 Thanks, guess I'll have to remove the blower...
If I want to clean evaporator - can I use foam cleaner and spray it into car air vent? Can I reach evaporator through center air vent?
I came across your channel and now I’m subscribed. Your vids are really cool and very informative. One question….are you selling your own brand of toothbrushes?
No, I don't have my own brand yet
Ok….LOL….I have a similar toothbrush I am now using for utility work as well!
Possible a dumb question:
I don’t remember seeing anything like that when I’m under the hood, is that stored under the dashboard? Like in between the engine bay and the infotainment system?
Edit: you mentioned the blower motor is under the dash, so that probably answered my question 😅
Could you please show us how to replace blower motor fan ?
I twisted it and pulled it out in the video. In the vehicle, you'd do the same under the passenger footwell
How did you research how it all works?
Thanks a lot
can you explain the difference in Honda accord, @ 3.11 sec, cross sectional view, In Honda accord, First filter comes, then blower motor and then evaporator, why this is different?
If the fan doesn't coold the condensor can the system be warm
It's the gas inside that makes it cool
Not the temperature of the fluid or pipes or condensor outside.
Huh, I didn't expect an auto mechanic to identify a potentiometer in electronics. You must be smarter than an average bear! :-D
He definitely is. Look at those custom-made props and charts he made with the car’s parts
He is a mechanical engineer!
Yep I sure am
My brother is an electrical engineer, some things rub off
If I understand this correctly, if the temperature gauge is set to lowest, then the cold air goes straight to the vents. If the temperature gauge is set a little higher, maybe 75 degrees, then the cold air gets mixed with hot air and blown to the vents
True, I tested on my Nissan Tiida with Auto mode. The lowest temp setting of 18 Celsius defaults to the upper vents. Higher Temps defaults to the lower foot vents. Also found if higher Temps are manually set fully to lower foot vents, a little heat exits the upper far left and right vents but not the middle upper two vents.
Your spiral gear is my "worm" gear. Just hope the plastic bit n pieces don't become brittle and crack and snap. I had two German cars and both had heater core issues
buried deep in the dash, to be fair they weren't young cars but even so.
notification squad!🔥🔥🔥
Thank you
Does a small bug could make any error to the system
It could
Quick question
Can having a bad wheel bearing cause brake pads to wear faster?
Yes, unevenly because the hub is no longer true and wobbles
May i ask a question, sorry for my ignorance but if the temperature switch only open de heat air, then is false that thing about the air in 24c sabes fuel and shit right? Like the compresor never stop working so is better just leave it at max cool
Yes
Only when the compressor is off you save fuel regardless of the mixer position.
@@speedkar99 thanks for the answer, i see so many people saying “oh no you need to put 24celsius because of the fuel consumption.
So when does the ac compressor stop working? If it doesn’t work like the ac of the wall, sorry for my english i’m a native spanish person
My ac compressor clutch wasn't engaging. I come to find out the PCM relay was physically damaged with a hole in it. I've been getting bad gas mileage I went ahead and replaced it. Now my Ac compressor engages it starts for 5 seconds and then stops and it keeps doing that every like few minutes. With ac turned max all I get is hot air. Do you think it's the relay? Low refrigerant? Bad ac compressor? Thanks in advance i liked the video and subbed!
Check the refrigerant
Are all AC found in hybrid car powered by the battery and not the engine connect by belt?
I have a 2020 Forte Kia when I turn on the heat the AC also automatically runs which I have to turn off the ac is that normal ?
Can we use PWM motor controller as the fan speed controller to have a wide range speed selection from 0 to 100%?
I also planning to make a custom hvac controller using Arduino, OLED screen and rotary encoder for my 1988 Cressida because the OEM control unit and wiring has been hardwired by the previous owner.
Can I replace the flap actuators with something like SG90 PWM servo so I can control the airflow using some microcontroller?
Yes. That's basically how it's controlled with automatic HVAC systems. See my other video on that
Brother when are you doing the TDI tear down?
Eventually when I get to it.... working on. Subaru WRX engine right now
as video show max cool on thermostat resistor 18c,but why when i measure air from aircond vent max can reach 4c before compressor cut off.
18C is the cabin temp not the air vent temp
@@speedkar99 i see.but one more question,the thermistor is attach on evap fin,how could it know when cabin tempreture is reach desire settting?all car is the same principle?
thanx
Welcome
Very nice video
But I have a question ,I didn’t understand the air flow path when recir- mode on?Thanks btw
Another question
How to know exactly the speed of air for each level (I’m simulating air flow on a software….)
I didnt find anything regarding this in the manual
Thanks...😍😍
Welcome