How to Read AC Schematics and Diagrams Basics

This video provides an overview of how to read AC schematics. We walk through some of the basics and most common symbols associated with reading air conditioner wiring diagrams.
Whenever you approach a wiring diagram, look at the whole thing, especially the legend and notes. In many cases, factory wiring will show up as solid lines and field wiring will show up as dashed lines. (Power wiring may be darker or bolder, and control wiring may be lighter.) In other words, solid lines indicate wires that are inside the appliance, and dashed lines indicate connections that you will have to make in the field. Component connections may be circular, and field splices may look a bit like wire nuts (and indicate where YOU will need to make a connection).
The legend also contains nomenclature to help you understand what the abbreviations really mean. In the case of this relatively universal Carrier wiring diagram, the asterisks by the abbreviations indicate that those respective parts may be factory-installed but may also be something that you'll have to add.
Schematics (ladder diagrams) differ from connection diagrams in that everything is shown between the two legs of power (L1 and L2). Schematics also have an inverted pyramid to indicate ground. The contactor's contacts are shown on separate sides on the schematics, but everything inside the contactor is shown together on the connection diagram. That's because the connection diagram shows how the components look within the unit instead of how power gets from one place to another. However, the components and connection points have the same names and numbers across both diagrams.
You can differentiate switch types based on what's beneath them. Thermal switches have squiggles, pressure switches have a bell, and float switches have a circle. Normally closed switches will appear closed on the diagrams, and normally open switches will appear open on diagrams. Low-pressure switches will have the line beneath the right-hand circle, and high-pressure switches will have the line above the right-hand circle. (In this case, the schematic had a typo.) Upside-down Y symbols on switches indicate a time delay.
One thing worth noting is that the letter C represents a common point; it does NOT mean the same thing on a run capacitor as it does on the compressor. On the compressor, C refers to the common point between the start and run windings. On the run capacitor, C refers to the common point between the compressor run capacitor and the condenser fan.
A short straight line followed by a curved line represents a capacitor. Spring-like symbols indicate that you are looking at an inductive or magnetic winding (usually in motors). On the other hand, jagged symbols indicate resistive loads, which generate light or heat instead of magnetism.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschoo...
Carrier: www.carrier.co...
Mitsubishi Cooling & Heating: www.mitsubishi...
Refrigeration Technologies: www.refrigtech...

[@eatcommies1375]

Not too many people have a way of explaining electrical schematics , You Sir have a talent for this IMO. Thank You!!

[@joshuat2751]

currently in my 2nd year of an apprentice program in a local college near me. This whole year is electrical and it was a bit confusing for me to read diagrams like this because my teacher never really goes too in depth with things and im more of a hands on learner , but this has made it sooooo much simpler. Glad my year one teacher that im still in touch with recommended your videos! :) Been outside on my own AC unit just getting a better visual for them and its pretty simple now. Thanks alot!

[@HVACS]

Good work!

[@MrGarcon98]

i am retired and my teacher was the same way ,,,,they are not all good at controls ! and to admit it is another thing ,,,,i love it when i am wrong this way i am hoping someone will correct me and i will learn something ,,,even a 68 years of age ,,,,just saying ,,,,,

[@00ABBITT00]

As a first year apprentice, I can’t say thank you enough for this.

[@mariomorua8141]

Thank you my friend for taking the time and effort in making these videos. It’s much appreciated.

[@cortlandtatt6750]

Great great teaching these R my problems understanding a schematics. You explain in a way it works for someone with no electrical schooling I just learned as I worked so great great ways of teaching, & for the negative comments if you all know that much then why even watch. Thank you I'll continued to watch your videos, with some questions.

[@yevgeniyburda1332]

This was the best video about schematics I ever saw . Thank you very much .

[@TheChuOi]

New subscriber. I watch your videos to help me understand HVAC and prepare me to enter the HVAC trade with a friend and enroll in APEX electrician school in NYC in April 2021.

[@user-hx5vh9uh2n]

I wish there was a hvac cert I could get by doing all your online vids. I completed an electrical apprenticeship school in 2015 in class 800 hour program. Would love to learn hvac too to add to my electrical troubleshooting and also to make me more valuable as maintenance manager at this resort I work at

[@bogger0017]

Man I'm glad you said something about the pressure switch typo! I sat there for like 5 minutes questioning if I had it all wrong when I was sure I had the down.

[@josiahpierson3636]

Good catch on the LPs and hps I've noticed little errors like that on schematics lol. You just shake your head

[@kylelikeskjvbible]

Its funny how for me as an electrical student, I learn more from HVAC guys than electricians LOL

[@rayzerot]

One of the running jokes in HVAC is that it's a combination of all the other trades. Plumbing, electrical, light carpentry, HVAC (obviously), sheet metal, etc. 😁

[@christianpederson7744]

Bro! I was an electrical apprentice for a year and then got into HVAC and it’s so much more complex it’s insane

[@lonsdaleslipons9570]

I am a qualified Electrician now installing bms wiring systems. The Schematics before the dotted line confuses me at times. Been doing it for a few years now but i really don't take the time i should to understand the ins and outs of how the hvac side works fully. We use Trend mostly but also distec honeywell and cylon. This was a helpful video. Thank you

[@Jeffrey-u2n]

You can learn much more from Electrical Technicians than from electricians.

[@acemenace7411]

Not funny that’s sad

[@robertmunguia250]

Awesome video. For someone who struggles with this it really helps. Please do more of these on carrier and Lennox.

[@vicferrari89]

Great job on this. I am using this for remote learning with my HVAC high school students during this trying time. Thanks for sharing!

[@robbiee.6921]

I'm a stationary engineer worked in a boiler room doing mostly mechanical stuff just started doing HVAC at a hospital I'm trying to learn schematics . Thank you

[@AlaskanMonroe]

Excellent video. Thank you for taking the time. If I can get this....anyone can. You teach very well sir. Thanks again!

[@miguelrojas3394]

Thanks Brian for the excellent explanation.🙏🙏🙏

[@resurgensix]

THANK YOU SO MUCH! This is a huge weak spot to create these diagrams, reading them is easier but not fn easy! It is like hearing Spanish and kind of getting it, but speaking.... much more difficult!

[@katoria69]

Thank you! It was very helpful! First year female hvac apprentice here 🙋🏽‍♀️ appreciate the video but damn you talked way too fast and it was hard for a newbie like me to keep up but I did learn so thank you!

[@aridematos3555]

You can adjust the tempo of the video at .075 at the settings of the video.

[@thisgame1499]

Good video. I would like to point out that all modern romex has 90c rated conductors so it could be used for this installation.

[@ኢትዮዽያዬ]

Thank you sir it’s a big help and crystal clear explanation

[@DJxDannee]

Awesome video Brian! You’re very thorough and easy to understand. 👍

[@TheEDNC]

I just LOVE “May be there” nomenclature!

[@emiliohuerta2658]

perfect job Man, God bless you

[@michaelcostello6991]

Great video. Please do more like this on control circuitry. What path does the crank case heater take when the contactor is open. Does it take a number of paths throught the motor windings

[@caru3257]

New contactor only one leg opens.

[@etherealrose2139]

It'll take every single path back to the source. So yes. Power will not flow if L1 and L2 aren't connected so there must be one, or multiple paths, between the two. Even when L1 closes.... though because other loads are on that line, the current splits proportionally and the CCH will have less current draw due to such high resistance (though current will still flow through it, it's a misnomer to say path of least resistance. That's how people get killed.) It's simply that the heater is just a big resistor so not much current will flow through when the other loads are running. it is almost negligible when it does travel through the motors, not enough to create any flux. There will be a voltage drop across the CCH as well (with L1/T1 open) as it'd be in series with the rest of the circuit. Once L1 closes, everything is in parallel so the voltage is the same for each, the CCH will draw some amps just not as much but likely drop out of the circuit anyways due to CHS opening shortly thereafter because it either heated up the oil or the compression will quickly get it heated up once running.

[@juanacosta2788]

Hey Brian great video man really helping me out get better at this 👍 👏

[@jollyscaria1922]

Vrey good welcomed

[@amedhossain6032]

You have explaind well, thank you Sir..

[@josephkokinda4251]

Sent to our DropBox for the guys. Thanks Bryan!

[@ultrafaga1947]

This video made me a better tech!

[@yeah-ro3rf]

Thanks for your endless lectures, really helps,can you please upload repairing and replacing compressor pistons,thanks

[@Itsmetahh]

was going a bit quick but great video.

[@glennsepelak5113]

good job.... 40 years in started in1981

[@danzelwesingtone7413]

very well explained tysm Sir...

[@teklesenbetgebreamlak7365]

Great teacher a appreciated so much lam technician to the field this diagnostics diagram helps alot

[@JohnDoe-jt9oq]

7:48 You can tell it's open on rise because imagine if water were rising beneath it, the beam would rise and open the contacts.

[@brianosegueda3622]

Thanks Brian... very helpful!

[@subbunathi2826]

Very nice explained thank you sir

[@Amos-vs6xv]

Good video braking down schematic symbols, thank you

[@mohammadwaseem523]

Nicely explained, keep sharing more and more lession

[@michaelcostello6991]

Great video. Very detailed.

[@hvac877]

Very good explanation thank you

[@vipinv8004]

Very Very Useful Sir

[@reyezkingz4123]

Thanks for the class

[@jfs520]

Thank you for sharing truly appreciate it

[@asiakevin]

Thank you, sir.

[@kevind159]

NM Romax is normally used in one- and two-family dwellings, and certain multifamily dwellings. NM-B is what you will see when shopping for NM cable, which is rated for 90 degrees C (194 degrees F).

[@MrGarcon98]

anything on circuit boards , other than if you have power to it and out of it its good ,,,,i think all teachers seem to use this as an explanation to those boards ,,,,thank you

[@dongyoungkim962]

Hi HVAC School, Can you please do a three-phase wiring diagram lecture for industrial refrigeration? A lot of people work in non-residential settings too!

[@tmst2199]

Playing this reminds of the scene in The Matrix when Neo gets his first Ju Jitsu training session. Unlike Neo, I'll have to do it several times before going up against a Carrier.

[@l.r.trammell1437]

Carrier sucks. York is the easiest to work on I've seen

[@Dillonmechanical]

Great video

[@teklesenbetgebreamlak7365]

Thankyou for the greatest explanation sir l really appreciated

[@solfugid7407]

Thank you very much I learned a lot.

[@mikeautostudent5562]

Thanks for your nice video. I hope you continue this as a series esp going to rooftop units as well.that will be very helpful. What is your trutech tools discount code?

[@JoseGuerrero-sj5ie]

Thank Bryan another great video sr.

[@proverbs2life]

I super apreciate this!

[@amt1298]

HVAC School I was wanting to better understand why Carrier has a Start Thermistor in parallel with the start capacitor and start relay. Thanks in advance!

[@shujaathussain7852]

Thank you sir, for some people your work is a beam of light in a moon free cloudy night. It would be better if colors of connecting wires, connectors are shown, if possible. Any way thank you.

[@JC-sc9rx]

what is the "E" that fell over that comes off of the OFM?

[@munawarsoomro8958]

This is excellent video. If you were in Dallas area and offered school, I'd take it.

[@alamzeb6342]

You are excellent Boss,

[@joro8604]

Well done

[@Clearview718]

month and a half into the trade here. All this stuff is so alien to me i have no idea how to understand this stuff. any advice??

[@hubercats]

Thank you!

[@rafaelquintana7160]

VERY USEFUL THANKS

[@henrybartlett1986]

Very good, as always.

[@HVACS]

Thanks again!

[@munawarsoomro8958]

This was an awesome video. Thanks

[@abdullahifatima2632]

Thank pls more on the pcb

[@rahmanyalshugaa3556]

Thank you for the information is helpful

[@kerryfat1697]

Thanks 🙏🏾

[@rjeternal]

This is fantastic. Thank you for doing this!

[@kosworkshop]

Why wouldn't they use a single pole contactor so you can have power to the crank case heater in the off duty cycle? Please and thank you...

[@sincityhvacr]

love you're videos been a fan for years but am having some low voltage issues on a carrier package unit trying to follow the wiring on the schematics but its crazy do u have any recommendations on how to get better at following and learning schematics

[@Livingcomfortinc]

Maybe you can do an advanced version. That would be awesome

[@SuccessIsEngineered]

Thank You

[@christianl5877]

8 month in as a service tech and still struggling to read schematics when no legend available. Are the symbols for field splice, control/field wiring etc universal for all schematics?

[@moisesbonilla9362]

Thank you sir! Great video!

[@kevonslims7269]

They use a single pole contractor simple for a path for the crank case heater..

[@5822huron]

Brian I need help with RTU Schematics

[@timstoriger3927]

My goal is to identify the functions of the devices in a given circuit diagram? Or spoken more general. How can I lean this general skill? When do I see a random circuit diagram in all kinds of electronic fields that I can recognize the devices and their functions? What is the best strategy to acquire this skill? Do you know good information recourses specially designated to acquire this skill? I do not want to handcraft things on my own and I do not want to study at a university to acquire a bachelor's degree in electrotechnology. I just want to be able to read more or less the circuit diagram. Thank you in advance

[@mohammadabdulfattah1867]

Thank you for this explanation, I don't know why some people make dislike

[@wildmandon1]

Did anyone else noticed the LPS and the HPS are different symbols on the Connection Diagram compared to Ladder Diagram. I believe the symbols on the Connection Diagram are correct. They are both normally closed switches. The LPS opens when the pressure drops while the HPS opens when the pressure increases. But, on the Ladder Diagram, I believe they are switched. Or, am I incorrect?

[@ajitashenoy2018]

You have explained the schematics and symbols very well but you have not explained how the power flows during start of compressor and fan and when it switches over to run bypassing the start capacitors.

[@1weirddoe571]

On my 1983 furnace wiring diagram, why is there one set of the air combustion (inducer) relay's normally open contacts in parallel with my fan control/limit-- the old style fan control type, that is? Why would the diagram say that call for heat turns on the blower right away and not let the fan switch do it in it's on time when it heats up? And it doesn't list like it's an optional wiring in the notes anywhere? But I'll bet if I go look on the furnace that there is no combustion relay across the fan switch so why is it in the diagram? It's a Heil diagram in the manual so why would heil print out a faulty diagram? I'll have to check to see if it's on the inside front cover panel also which I think it is so why would they do that?

[@휘센0187]

Greats!

[@romkan1714]

Thanks boss

[@johnbatchler8551]

Ur correct u have to scan what's on the schematic diagram this is for an account but I did it on radar the first thing I look is input

[@viswanathaniyer2372]

good video

[@mohammad45h]

سلام سپاس وهزاران تشکر از همه زحماتتون.👍...وهزاران هزار 👍.......جناب مهنس محترم امکان ترجمه زیر نویس بفارسی هست....ممنونم....

[@Jonabarr1]

Hi people, does anyone know a page where i could fin electrical diagrams of an old machine?, the AC is like 20 years old. Is the York sunline 2000.

[@caseanful]

Wow that's a lot to understand

[@rafaarroyo5438]

Thanks😁

[@crabwow8678]

Thank u

[@rissanew858]

All wiring diagrams BMW from 1998 to 2022 are in this application android (Bimma EWD)

[@leonardkimbler3689]

12:18 in your video you said you can look up a ptcr on this page and i can't seem to find it. any chance you can put it in a link. thanks and have a blessed day

[@juliusthewarrior4063]

new susbcriber bro here. I did not study about this even though I'm an aircondioning and refrigeration technician just a small unit not like hvac which its units are huge compared to window type and split type but I'm still learning do you agree?

[@linuxman0]

If you see mistakes on these schematics, do you ever contact the manufacturer and inform them of the mistake?

[@luislujan19771]

A serving the temp aware ess instead of actual trouble shooting des ription for an actual resident rather than a non res.. service tech podcast??

[@mohieali7317]

Fast but good

[@cumisatucumi8703]

Find more details => homewiringdiagram.blogspot.com/2019/01/3-way-light-switch-wiring-diagram.html

[@MrStress026]

1:49 😆

[@jmastercha]

slightly differnt from radar school... capacitor = --l l-- and not -l(-