Brian i love how clear and helpful you are to a tech who was on install for 1yr and now making my way to service tech. I have learned simple things just from watching your videos and the more difficult things being able to use that info in the field is huge. I have so many notes that really help me and i always ask questions to experienced techs when it comes to difficult situations. Thank you and please keep showing us what a service tech should know
Good teachers are like fine wine: hard to find. And you sir, are a good teacher. I've been watching your videos since I began working in OEM refrigeration manufacturing 3 years ago. I just got my first job as a HVACR service tech with my own vehicle and have doubled down on listening to this channel. Please feel free to share anything with me, I love this field and learning new things. I will do the same.
Thank you very much for all you do for us technicians. I just get the app and is AMAZING!! I am a HVAC company owner and all this classes are making me strong. Thank again!! I asked you if you please show me the proper way to flush a line set that can't be replace from r22 to 410a.
PRODIGY HVAC SCHOOL Thank you very much for sharing what you know with us. Very helpful information video Take care and have a great day PRODIGY HVAC SCHOOL From Nick Ayivor from London England UK 🇬🇧
Responding to RJ_Make’s question: Typically, heat causes resistance in a conductor, electrical connection (switch or contact) or an inductor (winding). In your question, your winding is cooling down - so resistance will decrease as a result of its cooling down. For EVERYONE ELSE: Voltage drop is a HORRIBLY difficult topic to explain to most folks. Some GET IT. Most…DON’T. Brian's reference to Ohm's Law is REALLY the best possible way to explain it, but the math must be applied while actually seeing it on a meter. AGAIN: Affirmation of what he's explaining can be seen by using a voltmeter and seeing it as a reading...using your brain's ingrained memory of Ohm's Law. DESPITE what Brian explains (and Brian has my greatest admiration for what he does), I've always impressed upon techs to remember Ohm Law like you'd remember how to brush your teeth. Make it an instinct. Make it something that's in your head EVERY TIME you put your test leads into a circuit. THEN - factor in the inductive aspect of that circuit (motors, relay coils, etc) when it wasn't what you’d expected. You may not know the math involving THAT, but at least it's something to be considered before calling a motor, solenoid, relay or contactor as BAD. With that, you might want to consider studying up on inductive loads. THE MOST IMPORTANT thing to remember is that a voltmeter, when you’ve introduced into a circuit, will only read a DIFFERENCE in potential between the two points being read. Applying what that "view" of what you're seeing in the circuit's performance, when compared to the OVERALL circuit's design...will give you a clue as to what's the problem. I've MOSTLY learned to use voltage drop to determine bad switches, contacts, fuses, circuit breakers, etc...as the ONLY way to find their failure. On that note… The NEXT MOST IMPORTANT thing to remember is to TRY to do your troubleshooting under the conditions which the problem occurs. That will inevitably be by using a voltmeter reading live voltages of 120v, 208v, 240v…or even 480v. I say this because an ohmmeter’s 9v battery usually won’t LABOR a circuit’s components adequately enough to duplicate the conditions under which a problem occurs. There’s not enough push from a 9vdc battery to duplicate the high-amp conditions demanded by a compressor, heating element…or whatever…to make it “fizzle” into the problem which occurred and you’re looking for. So, an ohmmeter…as handy as it is, often won’t tell all. A voltmeter will ALWAYS tell the true story - by looking for the VOLTAGE DROP. LASTLY: when troubleshooting…VERIFY!
@EC Tofix. Thanks for the great explanation. I'm a bit confused because of 5:38. As the **physical resistance** (say spinning up a blower wheel) increases so does heat right? So if heat is increasing why is my winding resistance decreasing according to 5:38? I missing something here..
@@RJMaker might want to understand conductive heat vs intended heat in a circuit, ie running a load generates heat, BUT stalling a fan motor (outside of design operation condition) the current is flowing through just one of the windings on the stator, creating inducted heat/ and eventually hopefully the fan will cut out on thermal overload before permanent damage occurs. This situation is where you will see resistance drop as it cools, vs normal operation as the wires would be sized to suit this.
For advanced techs ,you should do a video on the topic of Inductive reactance and power factor. Most techs get the dear in the head lights look if you ask them , why is an RMS meter better than others?
I’m missing something… where did it pass me? So how exactly do you perform a voltage drop test? By probing two ends and getting the voltage? I’d like to know how you determine the cause of the voltage drop. If I read 120 at an outlet but then get 86v once under load…aside from what’s plugged in, why is the voltage no longer 120 no matter what I plug in?
As heat decreases, resistance decreases? Sounds normal to me...but in all honesty, how big a change are we talking, as I imagine that conductor will not last for long...
I dont get it. At 9:07 with the switch OPEN you measured 120v at the top two points. Then at 9:30, you closed the switch and still measured 120v at the top points. How do you measure 120v at the top two points whether the switch is opened or closed??🤔🤔🤔🤔
The top two points are your source voltage.Your source should stay the same always in the circuit.The voltage across the switch is your voltage drop.If you add the voltage drops through out a circuit it should equal your source.
HVAC SCHOOL, The DVM meter can measure Back EMF voltage from the compressor motor but how can a technician know if the measured voltage is Forward Voltage or Back EMF Voltage? because the DVM meter won't tell you if its forward voltage or back EMF voltage. I'm not sure why when compressor motors start aging and slower RPMs the back EMF voltage will "increase" any reasons why the back EMF voltage increases?
A light bulb is an inductive load not a resistive load.I am confused.I have seen 120 volts on a coil and it would not pull in because it was not true power because of a bad switch that measured 0 volts across the switch.Thanks
so intuitively if I measure a volt or more of potential across a closed contacter (under load), I would classify that as an issue. That being said, I also think a motor can typically operate +/- 10% of its rated voltage rule of thumb. Who's to say that volt of potential is really an issue until the small amount of excess heat it produces further deteriorates the contact 3 years later? I guess I'm approaching the question from the angle of a customer paying for parts that may or may not make a difference for the longevity of the system so long as the load is receiving nameplate voltage. Do best practices sometimes deviate from the reality of the situation? I'm sure there're plenty of things I'm not considering i.e sacrificing a contactor before sacrificing a compressor. By the way, HVAC school is a great resource so thank you.
Most of this is just for you the tech to put into memory, for each job, (the ones where everything’s fine, but you can see it’s getting tired) where you can quietly consider the next call from them... obviously you replace things that you must, but don’t go losing sleep over it for the client.
If we are going to compare two different ac motors, can we always say that the one with higher amp (current) reading consumes more power? Or are there cases where the motor with lower amp reading actually uses more power?
When it comes to amps readings, you always have to be aware of the voltage level, since power (w/kw) is P=V*I*p.f. you can have a motor with higher power consumption at lower amp readings. Example: Assuming P.F. 0.9 Motor 1: Reads 5 Amps @220V ---> P=220[V]*5[A]*0.9 = 990 [W] Motor 2: Reads 3 Amps @480V----> P=480[V]*3[A]*0.9= 1296[W] So you see, you can have a motor with a lower reading of current but still have a higher power consumption.
@@ramos_dt At the same fixed voltage, lower amp readings should always mean lower power consumption, unless there's something wrong with the motor. Remember also that for three phase motors, power is calculated by P=V*I*√3*p.f.
But the 480v system is 3 phase, so you have 3 contactors and circuit breakers, yes you have lower current on one phase but if you group all the neutrals you should get a standard higher amp reading, identical to the phases in... if I’m not mistaken...but I’ll check on the next unit.. inductive motors give me more grief since it’s not straight forward to me yet...
Instead of using the term of voltage drop it’s much easier to understand and use the term differential your any gauge or meter only measures the differential between the two points including pressure gauges measure differential
I don’t get that neither. Physical resistance is inverse to electrical resistance. I always thought that when there is low resistance, there is low heat, but if you hold a fan motor and stop it from spinning and start to get hot, it’s not that motor getting hot due to the resistance increasing, just like a resistor gets hot, or a heating strip gets hot due to the high resistance in it. Let’s say that you have a fan and instead of you stopping it from spinning with your hand, you replace the wires to it to a size small enough so that wires start to get hot and burn. Wouldn’t you say that the wires burn because there is too much resistance in the wires? And like you said, resistance and current are inversely proportional of each other, given the voltage stays the same. Just like you mention in your video, your contactor contacts get pitted, causing high resistance, which also causes high amperage, which causes heat. Even the voltage drops a little bit. Anyway, I would really appreciate if you can educate me a bit more on this subject. I’m by no mean a collage or university graduate, I’m barely a practitioner of the trade that got a bit confused. Thanks.
@@thembones12 I am disappointed in the general lack of follow up in these comments, whether from fellow viewers or from the experts or the channel owners. But late as I may be, I will try to give you my take. What makes the wires hot is *too much current* . This is why a fuse melts. It is NOT resistance. Low resistance=high current. If you have a short circuit you have essentially zero resistance, which gives you infinite current. I=V/R so if R is 0 you are dividing by 0, which is undefined or infinity. Infinite current will quickly heat the wire and trip the breaker.
I agree it’s confusing. And I think he’s a bit loose with the term “work”. But I think his intentions are both correct, as they are two different examples with two different results. In the first case, with longer grass (more resistance) if you use the SAME amount of effort, he’s saying less work (ball distance) gets done. The ball doesn’t go as far compared to short grass. In the second case with long grass (more resistance), if you INCREASE effort, more work is done. Then the ball to goes the same distance compared to short grass.
wrong. you're conflating voltage drop with difference in potential. difference in potential is a broader notion whereas voltage drop refers to a decrease in voltage due to circuit components.
![[ 🔴LIVE ] Minecraft : Day1 ลุยโลกสี่เหลี่ยมกันนน](http://i.ytimg.com/vi/dt81BapyZLQ/mqdefault.jpg)
Good class, as an HVAC/R company owner I wished my guys new as much.
Glenn Sepelak teach them as he teaches his.
That kind of experience is expensive.
@@AlaskanMonroe oh i teach and train them for years, then they open up their own company everytime
I'm a 3rd year HVAC/R apprentice. I'm struggling. You make EXCELLENT instructional/explanatory videos. Thank you!
Brian i love how clear and helpful you are to a tech who was on install for 1yr and now making my way to service tech. I have learned simple things just from watching your videos and the more difficult things being able to use that info in the field is huge. I have so many notes that really help me and i always ask questions to experienced techs when it comes to difficult situations. Thank you and please keep showing us what a service tech should know
Good teachers are like fine wine: hard to find. And you sir, are a good teacher. I've been watching your videos since I began working in OEM refrigeration manufacturing 3 years ago. I just got my first job as a HVACR service tech with my own vehicle and have doubled down on listening to this channel. Please feel free to share anything with me, I love this field and learning new things. I will do the same.
I'm a second year HVAC/R student and just brushing up on the basics. Great videos and thank you!
Excellent voltage drop explanation, best I’ve seen.
I deal with 12 volts all day long in the automotive industry but it's totally awesome to see that ac electricity is the same as far as testing
Hi, Bryan I recently listen to your voltage drop video and wanted to say" Great info". And learned much from it. Thanks for all you do for your trade.
Best explanation so far. Awesome job!
Thank you very much for all you do for us technicians. I just get the app and is AMAZING!! I am a HVAC company owner and all this classes are making me strong. Thank again!!
I asked you if you please show me the proper way to flush a line set that can't be replace from r22 to 410a.
Excellent video. Voltage drop can be utilized as another way to diagnose a systems components.
PRODIGY HVAC SCHOOL
Thank you very much for sharing what you know with us. Very helpful information video
Take care and have a great day
PRODIGY HVAC SCHOOL
From Nick Ayivor from London England UK 🇬🇧
Responding to RJ_Make’s question:
Typically, heat causes resistance in a conductor, electrical connection (switch or contact) or an inductor (winding). In your question, your winding is cooling down - so resistance will decrease as a result of its cooling down.
For EVERYONE ELSE:
Voltage drop is a HORRIBLY difficult topic to explain to most folks. Some GET IT. Most…DON’T.
Brian's reference to Ohm's Law is REALLY the best possible way to explain it, but the math must be applied while actually seeing it on a meter.
AGAIN: Affirmation of what he's explaining can be seen by using a voltmeter and seeing it as a reading...using your brain's ingrained memory of Ohm's Law.
DESPITE what Brian explains (and Brian has my greatest admiration for what he does), I've always impressed upon techs to remember Ohm Law like you'd remember how to brush your teeth. Make it an instinct. Make it something that's in your head EVERY TIME you put your test leads into a circuit. THEN - factor in the inductive aspect of that circuit (motors, relay coils, etc) when it wasn't what you’d expected. You may not know the math involving THAT, but at least it's something to be considered before calling a motor, solenoid, relay or contactor as BAD.
With that, you might want to consider studying up on inductive loads.
THE MOST IMPORTANT thing to remember is that a voltmeter, when you’ve introduced into a circuit, will only read a DIFFERENCE in potential between the two points being read. Applying what that "view" of what you're seeing in the circuit's performance, when compared to the OVERALL circuit's design...will give you a clue as to what's the problem.
I've MOSTLY learned to use voltage drop to determine bad switches, contacts, fuses, circuit breakers, etc...as the ONLY way to find their failure. On that note…
The NEXT MOST IMPORTANT thing to remember is to TRY to do your troubleshooting under the conditions which the problem occurs. That will inevitably be by using a voltmeter reading live voltages of 120v, 208v, 240v…or even 480v.
I say this because an ohmmeter’s 9v battery usually won’t LABOR a circuit’s components adequately enough to duplicate the conditions under which a problem occurs. There’s not enough push from a 9vdc battery to duplicate the high-amp conditions demanded by a compressor, heating element…or whatever…to make it “fizzle” into the problem which occurred and you’re looking for.
So, an ohmmeter…as handy as it is, often won’t tell all. A voltmeter will ALWAYS tell the true story - by looking for the VOLTAGE DROP.
LASTLY: when troubleshooting…VERIFY!
@EC Tofix. Thanks for the great explanation. I'm a bit confused because of 5:38. As the **physical resistance** (say spinning up a blower wheel) increases so does heat right? So if heat is increasing why is my winding resistance decreasing according to 5:38? I missing something here..
Or as the Samurai says... "ohms can lie. Verify!"
@@RJMaker might want to understand conductive heat vs intended heat in a circuit, ie running a load generates heat, BUT stalling a fan motor (outside of design operation condition) the current is flowing through just one of the windings on the stator, creating inducted heat/ and eventually hopefully the fan will cut out on thermal overload before permanent damage occurs. This situation is where you will see resistance drop as it cools, vs normal operation as the wires would be sized to suit this.
Really informative and very well presented thank you so much.
That was very helpful! Thanks Bryan!
great video amigo...
For advanced techs ,you should do a video on the topic of Inductive reactance and power factor. Most techs get the dear in the head lights look if you ask them , why is an RMS meter better than others?
I’m missing something… where did it pass me? So how exactly do you perform a voltage drop test? By probing two ends and getting the voltage? I’d like to know how you determine the cause of the voltage drop. If I read 120 at an outlet but then get 86v once under load…aside from what’s plugged in, why is the voltage no longer 120 no matter what I plug in?
I have a question: On a hot winding why does my resistance continue to drop as the winding cools down?
As heat decreases, resistance decreases? Sounds normal to me...but in all honesty, how big a change are we talking, as I imagine that conductor will not last for long...
10:27 great tip ..
Good free info
15:52 great work cameraman lol
As always, great video. Thanks
I dont get it. At 9:07 with the switch OPEN you measured 120v at the top two points. Then at 9:30, you closed the switch and still measured 120v at the top points. How do you measure 120v at the top two points whether the switch is opened or closed??🤔🤔🤔🤔
The top two points are your source voltage.Your source should stay the same always in the circuit.The voltage across the switch is your voltage drop.If you add the voltage drops through out a circuit it should equal your source.
Good!
HVAC SCHOOL, The DVM meter can measure Back EMF voltage from the compressor motor but how can a technician know if the measured voltage is Forward Voltage or Back EMF Voltage? because the DVM meter won't tell you if its forward voltage or back EMF voltage. I'm not sure why when compressor motors start aging and slower RPMs the back EMF voltage will "increase" any reasons why the back EMF voltage increases?
A light bulb is an inductive load not a resistive load.I am confused.I have seen 120 volts on a coil and it would not pull in because it was not true power because of a bad switch that measured 0 volts across the switch.Thanks
so intuitively if I measure a volt or more of potential across a closed contacter (under load), I would classify that as an issue. That being said, I also think a motor can typically operate +/- 10% of its rated voltage rule of thumb. Who's to say that volt of potential is really an issue until the small amount of excess heat it produces further deteriorates the contact 3 years later? I guess I'm approaching the question from the angle of a customer paying for parts that may or may not make a difference for the longevity of the system so long as the load is receiving nameplate voltage. Do best practices sometimes deviate from the reality of the situation? I'm sure there're plenty of things I'm not considering i.e sacrificing a contactor before sacrificing a compressor. By the way, HVAC school is a great resource so thank you.
Most of this is just for you the tech to put into memory, for each job, (the ones where everything’s fine, but you can see it’s getting tired) where you can quietly consider the next call from them... obviously you replace things that you must, but don’t go losing sleep over it for the client.
I'm only in my first year but isn't your 'close on fall" switch for your compressor wrong? Shouldn't it be a "close on rise"?
Perfect instructions thanks!
Good stuff...
If you show the actual contact or with electricity may be more understand able
So new apprentice can relate to what they see in the field
If we are going to compare two different ac motors, can we always say that the one with higher amp (current) reading consumes more power? Or are there cases where the motor with lower amp reading actually uses more power?
When it comes to amps readings, you always have to be aware of the voltage level, since power (w/kw) is P=V*I*p.f. you can have a motor with higher power consumption at lower amp readings.
Example:
Assuming P.F. 0.9
Motor 1: Reads 5 Amps @220V ---> P=220[V]*5[A]*0.9 = 990 [W]
Motor 2: Reads 3 Amps @480V----> P=480[V]*3[A]*0.9= 1296[W]
So you see, you can have a motor with a lower reading of current but still have a higher power consumption.
How about motors with same voltage?
@@ramos_dt At the same fixed voltage, lower amp readings should always mean lower power consumption, unless there's something wrong with the motor.
Remember also that for three phase motors, power is calculated by P=V*I*√3*p.f.
Thank you.
But the 480v system is 3 phase, so you have 3 contactors and circuit breakers, yes you have lower current on one phase but if you group all the neutrals you should get a standard higher amp reading, identical to the phases in... if I’m not mistaken...but I’ll check on the next unit.. inductive motors give me more grief since it’s not straight forward to me yet...
Instead of using the term of voltage drop it’s much easier to understand and use the term differential your any gauge or meter only measures the differential between the two points including pressure gauges measure differential
Slow clap. Well done.
I don’t get that neither. Physical resistance is inverse to electrical resistance. I always thought that when there is low resistance, there is low heat, but if you hold a fan motor and stop it from spinning and start to get hot, it’s not that motor getting hot due to the resistance increasing, just like a resistor gets hot, or a heating strip gets hot due to the high resistance in it. Let’s say that you have a fan and instead of you stopping it from spinning with your hand, you replace the wires to it to a size small enough so that wires start to get hot and burn. Wouldn’t you say that the wires burn because there is too much resistance in the wires? And like you said, resistance and current are inversely proportional of each other, given the voltage stays the same. Just like you mention in your video, your contactor contacts get pitted, causing high resistance, which also causes high amperage, which causes heat. Even the voltage drops a little bit. Anyway, I would really appreciate if you can educate me a bit more on this subject. I’m by no mean a collage or university graduate, I’m barely a practitioner of the trade that got a bit confused. Thanks.
My thinking is same as your rationale. I am confused of Brian's explanation.
@@thembones12 I am disappointed in the general lack of follow up in these comments, whether from fellow viewers or from the experts or the channel owners. But late as I may be, I will try to give you my take.
What makes the wires hot is *too much current* . This is why a fuse melts. It is NOT resistance. Low resistance=high current. If you have a short circuit you have essentially zero resistance, which gives you infinite current. I=V/R so if R is 0 you are dividing by 0, which is undefined or infinity. Infinite current will quickly heat the wire and trip the breaker.
At first, I thought he had a cigarette
You contradict yourself at 3:35 and 4:04. So which is it?
I agree it’s confusing. And I think he’s a bit loose with the term “work”. But I think his intentions are both correct, as they are two different examples with two different results.
In the first case, with longer grass (more resistance) if you use the SAME amount of effort, he’s saying less work (ball distance) gets done. The ball doesn’t go as far compared to short grass.
In the second case with long grass (more resistance), if you INCREASE effort, more work is done. Then the ball to goes the same distance compared to short grass.
wrong. you're conflating voltage drop with difference in potential. difference in potential is a broader notion whereas voltage drop refers to a decrease in voltage due to circuit components.
Bro...just leave the camera alone ffs.