Bryan covers 5 misunderstood AC Run Capacitor facts and how a run capacitor works. Read all the tech tips, take the quizzes and find our handy calculators at www.hvacrschool.com
Thank you for explaining Capacitor related to AC. We had the AC tech tell us that our capacity was weakening but has not failed. We put off replacing it.
Glad to see that Bryan and Craig have collaborated on some videos. One may explain a topic differently and that difference may be what gets the light bulb to light . Keep up the great work guys.
Hear, hear. Your teaching is so outstanding, I very much appreciate your unselfish attitude. Many cannot afford colleges to learn a trade. Many had passed through a trade many years ago, like me, but new technologies have so quickly zoomed past and colleges don't cover areas like you do. Your clear teaching is very helpful and much appreciated. Thank you. Wow,!
It's actually pretty simple if you studied electricity and its applications. Unfortunately too many HVACR apprentices never did learn the basics! Hit the books, videos and if you need further help ask questions!
Thank you Brian for all your dedication to continuing education. Would you consider spending more time on inverter technology and specifically proper troubleshooting of these units ? I think we all can use more information on this technology.
Checking a cap while it's running is sometimes really clutch. I was on a roof the other day and there was no disconnect. I didn't want to climb down the ladder and search for a breaker, so I looked up your website and did it right there. SICK.
AC energy flows thru a capacitor just fine, but will cause a phase shift in timing due to its requirement to be charged up and discharged, this is needed to offset the starting and running winding so the motor can be driven in a direction of choice. If there were no start capacitor both running and starting winding will be energized at the same time and the motor will not have a reason to start in either direction. Don't concern yourself that the electrons don't flow across the separated plates because the energy itself passes right thru the capacitor delivering power to the start winding offset in time from the power being delivered to the running winding. Like he said energy flows thru a transformer with no connection as well. We use capacitors all the time in high frequencies as filters and such. In this case its strictly used as a timing shift component. Simply shut it off discharge it and measure its value with a meter no fancy math needed. Fail from heat really so what that is why we need AC, its not like we can control the heat in some way, unless you want to get an extension cord and keep the capacitor in by the A coil.
Great video!!! I looked in a condenser unit and it had a dual cap with a 60 MFD herm. Looking on repair clinic the model showed it should use a 30 MFD. The 60 MFD was out of spec but must have been in this unit for years. Should I replace with the 30 MFD? I did not look on the unit itself but need to do that too to see if the MFD is noted on the compressor. Trane model TTD760B100A2. Thanks!!
Thank you for the informative video. In theory, it should be possible to replace two single capacitors, a start cap of 30 uF, and a run cap of 5 uF with one dual capacitor of 30/5 uF in an A/C condenser, but is it possible in practice and would be there any disadvantages?
The capacitors on PSC motors used on compressors and fans on outdoor HVAC condensing units are always energized on most units. There is typically only one contact that opens that prevents the unit from running, but the other 120v feed is always energized. Does this arrangement actually contribute to wearing out the capacitors?
Could you kindly present a video on how to connect a external capacitor to an ac motor that does not have one. Can you just connect it to the power cord or does it have to be wired internally. Thanks !!
I have a coleman RV ac on the compresser start capacitor with a resistor in the one wire it is bad as well,, my question is do I need the resistor OR can I do away with it ??
E = I * Xc Capacitive Reactance (Xc) is calculated like this: Xc = 1 / (2 x pi x hz x farad) Xc = 1 / (2 x 3.1415 (pi) x 60 (hz) x farad) Xc = 0.0026527 x farad farad = 1,000,000 microfarads So 0.0026527 must be multiplied by 1,000,000 Xc = 0.0026527 ✕ 1,000,000 Xc = 2652.7 E = I x 2653 Formula : amps x 2653 / volts example - 4.8 amps x 2653 / 363 volts = 35.08 mfd
Ok. I understand that the run capacitor shifts the phase of the start windings and creates a rotating magnetic field to rotate the rotor. What happens when placing a hard start capacitor in parallel with the run capacitor? It increases the capacitance may times. How does that alter the phase shift?
I carry Turbo 200 and 200X. Dial in the correct values. It's a "no brainer". Plus, a 5 year warranty. Work smarter, not harder. Made in Palm Coast with German components.
Quick question. I understand the reason to match the microfarads size and voltage rating, but can a capacitor that is PHYSICALLY larger with the same electrical ratings be installed without issue? I believe it can be. Having a hard time finding an exact replacement for my PSC blower. Thanks
Just get the amperage at the start winding of each motor. For the compressor it’s the blue, hermetic wire going to the compressor and brown for OFM. Take your phone and multiply that amps by 2652. Then measure the voltage for that motor to C on the cap and remember it. Take your phone and divide the previous number by this voltage. It’s important to remember that this technique should not be used for troubleshooting but only to get an approximate value on a cap where the numbers are faded or not visible. I’ve found that this can be off by .5UF, which can be the difference between a condemning or not. Always verify with all cables removed and apply what you read online to become a better tech every day
How can a condenser run fine when the common wire from the top of the contactor to the capacitor has been burned and is no longer making any connection? If I remember it was the common wire. I’ve witnessed this twice and the system was seemingly running fine. I believe the spade terminals were loose and caused heat buildup and eventual burning of the wire. Just confused how they were kicking along fine without the wire.
Great Video. I have a question. I live in a 1500sqft condo in NJ. I have a central air. Rheem HVAC. It gets hot in summers. Especially, I have cathedral ceilings and sun-roof (skylight) in the living room. I set-up the thermostat at 70. And outside is 80. After running for almost 4-5hrs temp does not change. The living room is cool but the bedrooms does not get enough cooling. What could be potential reason - Air Filter (checked it is clean) - Capacitor - Dirty Condenser coil - Refrigerant. Just wanted to know before I call a technician. To see if I can DIY. Especially Air Filter, Capacitor, Condenser coil. Last time, I called for maintenance it set me back $700.
On the outside unit, is the suction line cold and sweating? What is the temp. of the air coming out of the indoor vents? What is the temp. of the air returning to the evaporator? When you checked the air filter, did you check to see if the evaporator fins were clean? Are the vents fully open in the bedrooms? Are there return grills in the bedrooms?
experiment with blocking registers to force cooler air to the bedroom. Not a great long term solution but might help evaluate the problem. This assumes the temperatures coming in and returning are within the specified range. You can buy magnetic covers that install over the inside of registers.
@@KENFEDOR22 I had a friend who said his ac was freezing up his freezing his evap coils. After checking the charge which was ok, I went around checking for closed vents. I found two unused bedrooms with vents blocked. He said nobody was using them, so he wanted to reduce his power bill. I told him he unbalanced system and could have wiped out compressor on liquid slugging. Dont block registers.
If the run capacitor is for shifting the electrical phase by 90 degrees so that it feeds the start winding, which is 90 degrees from the main winding, why are we concerned about power factor? I'm missing something. Please help. Thanks!
Actually the main purpose of the run capacitor in a psc motor is to improve the motor power factor when it is running. If you were to remove the run capacitor on a running motor it would continue to run albeit al lower power factor.
Don't confuse run with start. A start capacitor is for a single plus 1 auxiliary wound induction motor. With a single winding it is 50 50 which way the motor will start. By adding a smaller winding offset from the main and feeding that via a capacitor it is guaranteed which way the motor will start. A run capacitor is used with a 3 phase delta wired motor. By connecting line to one winding and connecting a capacitor across another, the motor will "see" a 3 phase supply.
Both inductors and capacitors change the phase of their current. Not only is the phase of the voltage changed reletive to the source,, but the current is changed too. In the caps case, voltage lags current.If we create a scenario where our voltage is peak, but our current is behind, the wave becomes a standing wave. Reflecting back and forth... caps aren't batteries, or a power source. They don't even have the ability to flow current. They simply lag voltage and lead current. Handy for resonant circuits and filters. They are the opposite of the inductor, who lags current and leads voltage.
Although capacitors don't boost voltage but they do bring in stability. How you might ask.. It is simple, they improve power factor. And I am talking about power factor capacitors in parallel to the lines and neutrals. To the back end on the grid side. When capacitors are employed on the motors and compressors. They reduce load or amperes and this can improve volts. For instance. I had power factor of 0.71 before power factor correction and in my commercial Enterprise I had 170-168 voltage almost all the time. Then, even though I had LPF penalty charges which were minimal for me. So, what I did was install three phase power factor correction capacitors on the motors. My voltage improved. You might ask how or why. The answer lies in the following reason; My load from motors was 20KVA. PF according to utility was 0.71. and my voltage used to be 170 in summers especially. When my 20 KVA after PF improvement came to 14KVA, from 0.71 to 0.96PF my voltage improved as the transformer wasn't overloaded as before. It stopped dropping to 170 volts in summers and came to stable level of 195-200. I had a lot of start and stops. So, with vfds it improved further. Now after some derating of capacitors in 2 years the PF is normal again at 0.91. still good enough. A little bit of calculation seems to be good. 83 amperes was the load based on 240 volts and 0.71 power factor. When it improved to 0.95. it dropped 24 amperes. 0.29 power factor correction improvement. 0.83. since power consumption remains same. Only KVA is reduced and changed to adjust to real power usage of around .95 therefore the voltage will be less. Around 60 Amperes. Since P=IV With 59 amperes the voltage adjusts to 230 as shown by the meter while at 83 amperes and power being same, the volts adjusted to 168 volts. The slight decrease more than calculation is due to conductor and length losses
It’s not just the lights you have to factor for. Just the lights alone 3 tons is more than enough for but only when properly installed and properly ducted. ( ONLY! ) What kind and how many watts of power are your dehumidifiers you’re going to use in the room that is part of the load calculation and BTUs Are you one of those guys who are going to have four wall fans on every wall with lots of airflow so you don’t have stagnant air what is the white power consumption of each one of those fan motors that adds heat to the room in BTUs. Are you one of those guys who believe in high humidity growth regiment vapor pressure deficit at 70+ percent humidity. Or are you one of those guys who believe in the high dry desert method of growing around 40% humidity. These are both very different grow procedures and heat loads because of your latent heat not your sensible heat. Will you have any other large motors in your room that consume lots of power like multiple large water pumps for under toe system or thin film nutrient system where the motors are on 24 seven inside the room you have to calculate in that added heat load. What is the house or building is it a single-story wooden house with next to no insulation on the roof with a south facing wall with no or little insulation and possibly painted dark brown or dark gray. I’ve seen rooms need an extra three or 4 tons just because of the color and lack of insulation in the building material used having nothing to do with the light load. Are you doing air room exchanges with large fans 24 seven what is the outside air temperature and humidity you have to take that in for consideration. Or are you doing 100% complete sealed rooms with no breathing with tanks of CO2 injection into the room on timers and CO2 sensors?. Are you located in North Dakota ? Are you located in Florida Are you located in the Arizona desert Or Denver Colorado up in the mountains Don’t think of just the lights as your heat load.
@@coldfinger459sub0 Really really appreciate your thorough response. I was certainly not thinking about many of the factors you pointed out. I’m gonna save your comment to refer to.
@@coldfinger459sub0 Do you have any recommendation ,a book or somewhere online, that would have good info on how to factor in everything you just said?
@@kregg2850 you can scroll through my UA-cam site littered in between all the automotive videos I’ll probably have a few videos you’re interested in. It’s kind of my specialty area here in San Francisco of agriculture for the last 30 years indoor grow
I have two identical AC units. One is close to the breaker box and the other is much farther away. The one closet to the breaker box loses a capacitor about every two years but the one that is farthest away has never had one fail. They both run about the same number of hours throughout the year. The current AC units are only 3 years old but the prior AC units that last 20 years did exactly the same thing. I believe the longer 240 volt leads to the farthest AC must be storing enough energy to keep that capacitor in good shape.
i can think of 2 possible reasons (it could be either or both): A) the far unit just has a stronger capacitor and/or the close one keeps getting ones that aren't as strong and by that i mean the voltage they can handle. there is always some manufacturing variability, even if they are the same part. B) the power having to go through that extra line gets a little bit weaker and it's easier on the capacitor. even if the voltage is the same, that's 60 hz, but there could be high-frequency voltage spikes that damage the capacitor and the longer line may reduce them to some degree. the short reason for that is that the long wire adds inductance in series with the AC and the thing with inductance is that it never wants to change the current. when one of those fast spikes tries to go through, the inductance might hamper that a little bit, similar to the shocks in a car. you still get the slow bumps but a lot of the fast stuff gets reduced pretty good.
On a single run capacitor, there are no markings for common and run. Does it matter which side is used for either? Ex. My ac compressor has a single run capacitor. The start wire goes to one side, and the common from the contactor to the other. Thanks
Does not matter. On the dual capacitors, there are actually two capacitors in one package. Each capacitor has two connections, just like your single capacitor terminals, but inside the package one of each is connected together or "Common" and brought out to a single terminal.
Herom pointed compersssr started point powed comeing and dis charge d comen ponit runinv due pointed us fan point fan using runing ruing point s . Started point herom comperssr st arted pointed .. due tuped fan
To all who say why would you want to use this method? This method allows the flexibility to check while running under a few circumstances: 1 a critical application where they don’t want to shut the system down while you check it. I haven’t been around mainframe computers in decades but I remember when they used to shut down things if the room temp exceeded a certain temp. 2 I have many times seen components that check good on a bench and fail under load. I am sure I’m not the Lone Ranger on that. This method gives you a real time, under load look at how the capacitor is performing. 3 It also lets you check running capacitor when you find yourself using a meter that can check amps and volts but not capacitance. Back in the day if you had an analog Simpson 260 you had a Cadillac of a meter. It did not do capacitance. If you had a capacitor on the bench you could only test for open, or if it pegged the meter and stayed there, or was grounded to the case or watch the cap charge and discharge by watching the meter cycle rising and returning to zero. That did not tell you what the capacitance was, just that it would charge and discharge. I know I just dated myself and I am ready for the jokes but no I did not personally know Jesus, Moses or Methuselah.
It’s still the Cadillac of meters, I have a Sperry, doesn’t have the taught band suspension needle like the Simpson but I bought it when I started in refrigeration in 1975 and I’m still using it these days.
By itself in an AC circuit, all a capacitor does is give a phase shift, with no change in the shape or magnitude of the typical sinusoidal waveform. The magic happens when used in parallel or series with an inductor, like a motor. Depending on the configuration, it can increase or reduce overall current, and it can correct power factor to provide more efficient energy transfer. When used in parallel it can allow electrons to shift in resonance back and forth between the inductor and the cap while driving the motor. This has the effect of reducing overall power consumption by increasing overall impedance.
Heat. It's the killer of all things. Easy as that. There's different types of capacitors for what it's worth. And different quality of builds and materials. Just one of those things that is cheaper to mass produce crop quality and replace than spend extra dough on a good one.
Ok here is a possible myth. But could be true. I have been told you can go up on the compressor capacitor size by 5 microfarads. Now if you’re using a turbo 200X and are trying to make a 45/5 connection it says to use the 50MFD terminal. So i would think it was ok. But I’d like to see what the pros think.
You can check a capacitor while it's running. Me: OH?! Measure the amperage on the start winding and multiply by... Me: Wait what? It's okay just multiply and divide by... Me: I'll just turn it off, never mind.
It's very easy, more efficient, eliminates hooking wires back incorrectly and eliminates bending/loosening the spade terminals. Multiple 2652 x the amp draw of the herm or fan wire, depends which side of the capacitor you're checking, then divide by the voltage between the C and herm or fan terminal. Make a cheat sheet till it becomes second nature.
@@morganf3200 Your initial reply "Yeah screw that, just pull the disconnect and check it 😂" and you say for me not to be a moron? Looks like someone can't do math, doesn't want to improve, to dumb to remember the steps or doesn't want their hands in the control panel. HVAC School videos offer information for us to be able to improve as technicians so I don't understand why you are hear. Oh, to hurl insults at people and make yourself feel like the man you are only in your dreams. Get back to work "capacitor changer".
@@saurisco338 You can Google and get bogged down in the weeds if you want to be a math major. Not too important. They are known as "constants", they stay the same every time you do the math.
What I meant to say was what if the normal volts, coupled with the back emf, start exceeding the rated volt rating. I see this happen a lot. @@Sylvan_dB
Since it is not switched out after start up, the "start" winding is strictly speaking the auxiliary winding. The run capacitor provides the delay in the current between the run winding and aux winding to create the magnetic field difference to start the rotor turning, but then while the motor is running the run cap was chosen by the designers to provide the most circular magnetic field profile between the run and aux winding at the design load for the most efficient operation. The more the field profile is unbalanced, the more heat losses and motor stress. Essentially, the run cap "tunes" the PSC motor for the most efficient operation at design load. When the cap starts going bad, or the wrong size MFD one is installed, more of the power goes to heat in the windings instead of rotation and eventual motor failure.
DC systems still are. In AC current flows both ways. Makes no sense to polarize an Alternating Current capacitor. It's primary use is phase shifting not storage and release of energy (though technically it does that 60 times per second) It also smooths the ripple some.
Ooof so close. It charges and discharges 60 times per second. It simply doesn't store energy like we think of it in a DC system. It is used for shifting the phase angle in order to create a rotational force upon the rotor. I'm sure you know that but using the phrase "think of it as an energy storage device" is as erroneous as thinking it somehow changes voltage to any appreciable degree. Good video otherwise.
A capacitor is an energy storing device there is nothing wrong with that statement! Whether is connected to AC or DC voltage thisdoes not alter the fact that the capacitor is storing energy by the virtue of creating an electric field.
Could you kindly present a video on how to connect a external capacitor to an ac motor that does not have one. Can you just connect it to the power cord or does it have to be wired internally. Thanks !!
Love this format. Great video
Thank you for explaining Capacitor related to AC. We had the AC tech tell us that our capacity was weakening but has not failed. We put off replacing it.
Brian you are simply a Great A/C
Instructor an Encyclopedia of
A/C conditions.
Thank You
Glad to see that Bryan and Craig have collaborated on some videos. One may explain a topic differently and that difference may be what gets the light bulb to light . Keep up the great work guys.
Very informative! This guy is a GURU in this field:).
Love this channel! Keep it coming! Thanks for your contribution to our trade! Great work!
Thank you for your ongoing dedication to educating HVAC techs helping make us better at what we do. I am grateful and hope you never stop doing it.
Hear, hear. Your teaching is so outstanding, I very much appreciate your unselfish attitude. Many cannot afford colleges to learn a trade. Many had passed through a trade many years ago, like me, but new technologies have so quickly zoomed past and colleges don't cover areas like you do. Your clear teaching is very helpful and much appreciated. Thank you. Wow,!
Channels like this and ACservicetech make you feel like a damn physicist lol... there's just so much science involved in HVAC. It's awesome
It's actually pretty simple if you studied electricity and its applications. Unfortunately too many HVACR apprentices never did learn the basics! Hit the books, videos and if you need further help ask questions!
You do a great job in your explanations and level of detail
Thank you Brian for all your dedication to continuing education. Would you consider spending more time on inverter technology and specifically proper troubleshooting of these units ? I think we all can use more information on this technology.
Great explanation clears up a misunderstood subject 👍
I really love this channel
Checking a cap while it's running is sometimes really clutch. I was on a roof the other day and there was no disconnect. I didn't want to climb down the ladder and search for a breaker, so I looked up your website and did it right there. SICK.
This is such a simple and clear, yet rare information. Thanks for the time to put these information together.
Thanks for reviewing this all important topic.
Excellent explanation.
Great video. Thanks for sharing.
Wow, super informative!
great information
Another awesome straight to the point but detailed video, thanks Brian. Quick question, is there a brand of capacitors you recommend?
Thanks that example really helped along with the explanation. Now add a 521 to it and lets see how all of that works together.
Great video!
Quick and informative
Great information.
Get your guys to study “ Power factor” and this will really drive home the role of a capacitor in an inductive circuit. Great video.
The art of phase shifting...
Very good job 👍
Very good information
Very good information bro keep it up God bless
Thank You!
You guys are great 👍
Love this one.
AC energy flows thru a capacitor just fine, but will cause a phase shift in timing due to its requirement to be charged up and discharged, this is needed to offset the starting and running winding so the motor can be driven in a direction of choice. If there were no start capacitor both running and starting winding will be energized at the same time and the motor will not have a reason to start in either direction. Don't concern yourself that the electrons don't flow across the separated plates because the energy itself passes right thru the capacitor delivering power to the start winding offset in time from the power being delivered to the running winding. Like he said energy flows thru a transformer with no connection as well. We use capacitors all the time in high frequencies as filters and such. In this case its strictly used as a timing shift component. Simply shut it off discharge it and measure its value with a meter no fancy math needed. Fail from heat really so what that is why we need AC, its not like we can control the heat in some way, unless you want to get an extension cord and keep the capacitor in by the A coil.
Nice job and video
Love the guitar intro
Thanks for the added knowledge 👍
Great video!!! I looked in a condenser unit and it had a dual cap with a 60 MFD herm. Looking on repair clinic the model showed it should use a 30 MFD. The 60 MFD was out of spec but must have been in this unit for years. Should I replace with the 30 MFD? I did not look on the unit itself but need to do that too to see if the MFD is noted on the compressor. Trane model TTD760B100A2. Thanks!!
what are your thoughts/opinion on a soft start kit for systems? Thanks!!!
Wow Amazing video
Iove You sir
The start winding is , after it is used to start the motor, becomes a second phase ,with the help of the run cap . It is in effect a two phase motor.
Thank you for the informative video. In theory, it should be possible to replace two single capacitors, a start cap of 30 uF, and a run cap of 5 uF with one dual capacitor of 30/5 uF in an A/C condenser, but is it possible in practice and would be there any disadvantages?
The capacitors on PSC motors used on compressors and fans on outdoor HVAC condensing units are always energized on most units. There is typically only one contact that opens that prevents the unit from running, but the other 120v feed is always energized. Does this arrangement actually contribute to wearing out the capacitors?
Very niece sir
Yep great content
Could you kindly present a video on how to connect a external capacitor to an ac motor that does not have one. Can you just connect it to the power cord or does it have to be wired internally. Thanks !!
So ac capacitor don’t store energy you say but why dose my ac capacitor shack me so bad when I connected it to the main and remove it
Can u still use a capacitor thats reading a higher mfd on ur multimeter than whats listed on the capacitor? N no bleed resistor connected.
buenos videos
Would a bad running capacitor on a motor cause the breaker to trip?
Very good to know. Now I can take better care of the one in my air conditioner. tech companies charge a lot
I have a coleman RV ac on the compresser start capacitor with a resistor in the one wire it is bad as well,, my question is do I need the resistor OR can I do away with it ??
If the split run side of the capacitor is weak, will a new capacitor result in the ac blowing cooler air?
These short videos are so informative. Where do the numbers in that equation come from? What does the 26520 and 3183 represent.
E = I * Xc
Capacitive Reactance (Xc) is calculated like this:
Xc = 1 / (2 x pi x hz x farad)
Xc = 1 / (2 x 3.1415 (pi) x 60 (hz) x farad)
Xc = 0.0026527 x farad
farad = 1,000,000 microfarads
So 0.0026527 must be multiplied by 1,000,000
Xc = 0.0026527 ✕ 1,000,000
Xc = 2652.7
E = I x 2653
Formula :
amps x 2653 / volts
example - 4.8 amps x 2653 / 363 volts = 35.08 mfd
Not important, they are known as constants. If you're in the U.S. you need 2652 for 60Hz. Just remember, 2652 x amperage divided by voltage.
@@jeffb8437: Save time and money; change the damned capacitor!
@@jeffb8437now do reactive capacitance.
@@bill944I knew Constance back in high school. Big girl. She lost weight after graduation.
Can I use a 55/5 where there was a 45/5 ?
0:25 capacitor is a device that stores a differential charge on opposing plates ; not a voltage booster
Ok. I understand that the run capacitor shifts the phase of the start windings and creates a rotating magnetic field to rotate the rotor. What happens when placing a hard start capacitor in parallel with the run capacitor? It increases the capacitance may times. How does that alter the phase shift?
What's the difference between "in and out" vs "through"?
I carry Turbo 200 and 200X. Dial in the correct values. It's a "no brainer". Plus, a 5 year warranty. Work smarter, not harder. Made in Palm Coast with German components.
what does 35 + 7.5 mean on a capacitor? Is it both 35 mfd and 7.5 mfd? If so are there separate terminals that let you choose one or the other?
Nice!)
Anybody wondering where the 2652 comes from ? It’s (1/(2*pi*f))*1000000 when f=60hz.
Quick question. I understand the reason to match the microfarads size and voltage rating, but can a capacitor that is PHYSICALLY larger with the same electrical ratings be installed without issue? I believe it can be. Having a hard time finding an exact replacement for my PSC blower. Thanks
Yes it's fine. Only the rating maters. Physical size varies greatly.
@@saulm1257 Thanks for confirming my thought on the matter.
Absolutely in this case size does not matter!
Can you go into more details about measuring the mfd while the system is running?
Look in the HVAC School playlists. They have a video dedicated to this topic.
Just get the amperage at the start winding of each motor. For the compressor it’s the blue, hermetic wire going to the compressor and brown for OFM. Take your phone and multiply that amps by 2652. Then measure the voltage for that motor to C on the cap and remember it. Take your phone and divide the previous number by this voltage. It’s important to remember that this technique should not be used for troubleshooting but only to get an approximate value on a cap where the numbers are faded or not visible. I’ve found that this can be off by .5UF, which can be the difference between a condemning or not. Always verify with all cables removed and apply what you read online to become a better tech every day
@@peepeepoopoo1399 : Always become a better tech!
How can a condenser run fine when the common wire from the top of the contactor to the capacitor has been burned and is no longer making any connection? If I remember it was the common wire.
I’ve witnessed this twice and the system was seemingly running fine. I believe the spade terminals were loose and caused heat buildup and eventual burning of the wire. Just confused how they were kicking along fine without the wire.
I have had the same experience many times. Vibration can cause such problems.
Great Video. I have a question.
I live in a 1500sqft condo in NJ. I have a central air. Rheem HVAC. It gets hot in summers. Especially, I have cathedral ceilings and sun-roof (skylight) in the living room. I set-up the thermostat at 70. And outside is 80. After running for almost 4-5hrs temp does not change. The living room is cool but the bedrooms does not get enough cooling.
What could be potential reason
- Air Filter (checked it is clean)
- Capacitor
- Dirty Condenser coil
- Refrigerant.
Just wanted to know before I call a technician. To see if I can DIY. Especially Air Filter, Capacitor, Condenser coil. Last time, I called for maintenance it set me back $700.
On the outside unit, is the suction line cold and sweating? What is the temp. of the air coming out of the indoor vents? What is the temp. of the air returning to the evaporator? When you checked the air filter, did you check to see if the evaporator fins were clean? Are the vents fully open in the bedrooms? Are there return grills in the bedrooms?
experiment with blocking registers to force cooler air to the bedroom. Not a great long term solution but might help evaluate the problem. This assumes the temperatures coming in and returning are within the specified range. You can buy magnetic covers that install over the inside of registers.
@@KENFEDOR22 I had a friend who said his ac was freezing up his freezing his evap coils. After checking the charge which was ok, I went around checking for closed vents. I found two unused bedrooms with vents blocked.
He said nobody was using them, so he wanted to reduce his power bill. I told him he unbalanced system and could have wiped out compressor on liquid slugging. Dont block registers.
If the run capacitor is for shifting the electrical phase by 90 degrees so that it feeds the start winding, which is 90 degrees from the main winding, why are we concerned about power factor? I'm missing something. Please help. Thanks!
Actually the main purpose of the run capacitor in a psc motor is to improve the motor power factor when it is running. If you were to remove the run capacitor on a running motor it would continue to run albeit al lower power factor.
Don't confuse run with start.
A start capacitor is for a single plus 1 auxiliary wound induction motor. With a single winding it is 50 50 which way the motor will start. By adding a smaller winding offset from the main and feeding that via a capacitor it is guaranteed which way the motor will start.
A run capacitor is used with a 3 phase delta wired motor. By connecting line to one winding and connecting a capacitor across another, the motor will "see" a 3 phase supply.
Both inductors and capacitors change the phase of their current. Not only is the phase of the voltage changed reletive to the source,, but the current is changed too. In the caps case, voltage lags current.If we create a scenario where our voltage is peak, but our current is behind, the wave becomes a standing wave. Reflecting back and forth... caps aren't batteries, or a power source. They don't even have the ability to flow current. They simply lag voltage and lead current. Handy for resonant circuits and filters. They are the opposite of the inductor, who lags current and leads voltage.
Although capacitors don't boost voltage but they do bring in stability. How you might ask.. It is simple, they improve power factor. And I am talking about power factor capacitors in parallel to the lines and neutrals. To the back end on the grid side. When capacitors are employed on the motors and compressors. They reduce load or amperes and this can improve volts. For instance. I had power factor of 0.71 before power factor correction and in my commercial Enterprise I had 170-168 voltage almost all the time. Then, even though I had LPF penalty charges which were minimal for me. So, what I did was install three phase power factor correction capacitors on the motors. My voltage improved. You might ask how or why. The answer lies in the following reason;
My load from motors was 20KVA. PF according to utility was 0.71. and my voltage used to be 170 in summers especially. When my 20 KVA after PF improvement came to 14KVA, from 0.71 to 0.96PF my voltage improved as the transformer wasn't overloaded as before. It stopped dropping to 170 volts in summers and came to stable level of 195-200. I had a lot of start and stops. So, with vfds it improved further. Now after some derating of capacitors in 2 years the PF is normal again at 0.91. still good enough.
A little bit of calculation seems to be good.
83 amperes was the load based on 240 volts and 0.71 power factor. When it improved to 0.95. it dropped 24 amperes. 0.29 power factor correction improvement. 0.83. since power consumption remains same. Only KVA is reduced and changed to adjust to real power usage of around .95 therefore the voltage will be less. Around 60 Amperes. Since P=IV
With 59 amperes the voltage adjusts to 230 as shown by the meter while at 83 amperes and power being same, the volts adjusted to 168 volts. The slight decrease more than calculation is due to conductor and length losses
Great vid. Curious on hvac schools thoughts on proper unit sizing. How would you factor in 10 1000w hps lights? 😏🤫
It’s not just the lights you have to factor for. Just the lights alone 3 tons is more than enough for but only when properly installed and properly ducted. ( ONLY! )
What kind and how many watts of power are your dehumidifiers you’re going to use in the room that is part of the load calculation and BTUs
Are you one of those guys who are going to have four wall fans on every wall with lots of airflow so you don’t have stagnant air what is the white power consumption of each one of those fan motors that adds heat to the room in BTUs.
Are you one of those guys who believe in high humidity growth regiment vapor pressure deficit at 70+ percent humidity.
Or are you one of those guys who believe in the high dry desert method of growing around 40% humidity. These are both very different grow procedures and heat loads because of your latent heat not your sensible heat.
Will you have any other large motors in your room that consume lots of power like multiple large water pumps for under toe system or thin film nutrient system where the motors are on 24 seven inside the room you have to calculate in that added heat load.
What is the house or building is it a single-story wooden house with next to no insulation on the roof with a south facing wall with no or little insulation and possibly painted dark brown or dark gray.
I’ve seen rooms need an extra three or 4 tons just because of the color and lack of insulation in the building material used having nothing to do with the light load.
Are you doing air room exchanges with large fans 24 seven what is the outside air temperature and humidity you have to take that in for consideration.
Or are you doing 100% complete sealed rooms with no breathing with tanks of CO2 injection into the room on timers and CO2 sensors?.
Are you located in North Dakota ?
Are you located in Florida
Are you located in the Arizona desert
Or Denver Colorado up in the mountains
Don’t think of just the lights as your heat load.
@@coldfinger459sub0 Really really appreciate your thorough response. I was certainly not thinking about many of the factors you pointed out. I’m gonna save your comment to refer to.
@@coldfinger459sub0 Do you have any recommendation ,a book or somewhere online, that would have good info on how to factor in everything you just said?
@@kregg2850 you can scroll through my UA-cam site littered in between all the automotive videos I’ll probably have a few videos you’re interested in.
It’s kind of my specialty area here in San Francisco of agriculture for the last 30 years indoor grow
@@coldfinger459sub0 I had to laugh at the oddly specific response. Someone knows how wild grow rooms can get lol. Way too smelly for me
i=C(dv/dt)
Super
I have two identical AC units. One is close to the breaker box and the other is much farther away. The one closet to the breaker box loses a capacitor about every two years but the one that is farthest away has never had one fail. They both run about the same number of hours throughout the year. The current AC units are only 3 years old but the prior AC units that last 20 years did exactly the same thing. I believe the longer 240 volt leads to the farthest AC must be storing enough energy to keep that capacitor in good shape.
i can think of 2 possible reasons (it could be either or both):
A) the far unit just has a stronger capacitor and/or the close one keeps getting ones that aren't as strong and by that i mean the voltage they can handle. there is always some manufacturing variability, even if they are the same part.
B) the power having to go through that extra line gets a little bit weaker and it's easier on the capacitor. even if the voltage is the same, that's 60 hz, but there could be high-frequency voltage spikes that damage the capacitor and the longer line may reduce them to some degree. the short reason for that is that the long wire adds inductance in series with the AC and the thing with inductance is that it never wants to change the current. when one of those fast spikes tries to go through, the inductance might hamper that a little bit, similar to the shocks in a car. you still get the slow bumps but a lot of the fast stuff gets reduced pretty good.
On a single run capacitor, there are no markings for common and run. Does it matter which side is used for either? Ex. My ac compressor has a single run capacitor. The start wire goes to one side, and the common from the contactor to the other. Thanks
Does not matter. On the dual capacitors, there are actually two capacitors in one package. Each capacitor has two connections, just like your single capacitor terminals, but inside the package one of each is connected together or "Common" and brought out to a single terminal.
Can I replace a compacitor of +_ 6% with a +_5%
The herm is not the fan side. (ref. time mark 1:43). The Herm connects to the compressor.
Herom pointed compersssr started point powed comeing and dis charge d comen ponit runinv due pointed us fan point fan using runing ruing point s . Started point herom comperssr st arted pointed .. due tuped fan
To all who say why would you want to use this method?
This method allows the flexibility to check while running under a few circumstances:
1 a critical application where they don’t want to shut the system down while you check it. I haven’t been around mainframe computers in decades but I remember when they used to shut down things if the room temp exceeded a certain temp.
2 I have many times seen components that check good on a bench and fail under load. I am sure I’m not the Lone Ranger on that. This method gives you a real time, under load look at how the capacitor is performing.
3 It also lets you check running capacitor when you find yourself using a meter that can check amps and volts but not capacitance.
Back in the day if you had an analog Simpson 260 you had a Cadillac of a meter. It did not do capacitance. If you had a capacitor on the bench you could only test for open, or if it pegged the meter and stayed there, or was grounded to the case or watch the cap charge and discharge by watching the meter cycle rising and returning to zero. That did not tell you what the capacitance was, just that it would charge and discharge.
I know I just dated myself and I am ready for the jokes but no I did not personally know Jesus, Moses or Methuselah.
It’s still the Cadillac of meters, I have a Sperry, doesn’t have the taught band suspension needle like the Simpson but I bought it when I started in refrigeration in 1975 and I’m still using it these days.
@@nunyabusiness6746 The problem with analog is old eyesight. 😁
capacitor take the bumps out of the inverted sign wave on pulsing ac current - balances or flattens out the top of the wave length
By itself in an AC circuit, all a capacitor does is give a phase shift, with no change in the shape or magnitude of the typical sinusoidal waveform. The magic happens when used in parallel or series with an inductor, like a motor. Depending on the configuration, it can increase or reduce overall current, and it can correct power factor to provide more efficient energy transfer. When used in parallel it can allow electrons to shift in resonance back and forth between the inductor and the cap while driving the motor. This has the effect of reducing overall power consumption by increasing overall impedance.
@@spelunkerd I think We both said the same thing except mind was not as technical and in very simple terms
Why does the run oil capacitor fail so often ?? I have many used capacitor that are many years old and still good. How can you clarify this ??? Thanks
Heat. It's the killer of all things. Easy as that. There's different types of capacitors for what it's worth. And different quality of builds and materials. Just one of those things that is cheaper to mass produce crop quality and replace than spend extra dough on a good one.
@@etherealrose2139 Thanks
Ok here is a possible myth. But could be true. I have been told you can go up on the compressor capacitor size by 5 microfarads. Now if you’re using a turbo 200X and are trying to make a 45/5 connection it says to use the 50MFD terminal. So i would think it was ok. But I’d like to see what the pros think.
I’m still confused as I thought compressors needed a start capacitor. Dual run capacitors indicate RUN, so where is the START CAPACITOR?
So If I put a a 80/5 ohm on a 70 ohm what’s expected to happen.
im wondering about the same thing, usully they say + - 5~10% is ok. so thats just little over 10%.
👍👍
💪🏼
You can check a capacitor while it's running.
Me: OH?!
Measure the amperage on the start winding and multiply by...
Me: Wait what?
It's okay just multiply and divide by...
Me: I'll just turn it off, never mind.
Electricity does not take the path of least resistance, but I see most humans do.
It's very easy, more efficient, eliminates hooking wires back incorrectly and eliminates bending/loosening the spade terminals. Multiple 2652 x the amp draw of the herm or fan wire, depends which side of the capacitor you're checking, then divide by the voltage between the C and herm or fan terminal. Make a cheat sheet till it becomes second nature.
@@morganf3200 Your initial reply "Yeah screw that, just pull the disconnect and check it 😂" and you say for me not to be a moron? Looks like someone can't do math, doesn't want to improve, to dumb to remember the steps or doesn't want their hands in the control panel. HVAC School videos offer information for us to be able to improve as technicians so I don't understand why you are hear. Oh, to hurl insults at people and make yourself feel like the man you are only in your dreams. Get back to work "capacitor changer".
Where do the 3183 and 2652 come from?
@@saurisco338 You can Google and get bogged down in the weeds if you want to be a math major. Not too important. They are known as "constants", they stay the same every time you do the math.
Say the system has a oem capacitor that's 370v but later the motor starts pulling more than 370v. Should you change to a 440v?
Motor does not "pull" voltage. Voltage is supplied or pushed to the motor. Unless you change the supply voltage, the OEM cap specs are sufficient.
What I meant to say was what if the normal volts, coupled with the back emf, start exceeding the rated volt rating. I see this happen a lot. @@Sylvan_dB
Junior techs = capacitor changers
😂😅!!!
OK. So why is a run capacitor wired to the start winding?
It acts as a 3rd phase, helping to make sure the motor spins in the right direction.
Since it is not switched out after start up, the "start" winding is strictly speaking the auxiliary winding. The run capacitor provides the delay in the current between the run winding and aux winding to create the magnetic field difference to start the rotor turning, but then while the motor is running the run cap was chosen by the designers to provide the most circular magnetic field profile between the run and aux winding at the design load for the most efficient operation. The more the field profile is unbalanced, the more heat losses and motor stress.
Essentially, the run cap "tunes" the PSC motor for the most efficient operation at design load. When the cap starts going bad, or the wrong size MFD one is installed, more of the power goes to heat in the windings instead of rotation and eventual motor failure.
@@jkbrown5496
Thank you!
Best explanation ever
I'll keep checking while the power is disconnected thanks!😄😳🥃😆😂😆🥃👍
Stay safe.
Retired keyboard super tech.
Wear your safety glasses.
2:29
Why are capacitors not polarized like they were in the older days?
DC systems still are.
In AC current flows both ways. Makes no sense to polarize an Alternating Current capacitor. It's primary use is phase shifting not storage and release of energy (though technically it does that 60 times per second) It also smooths the ripple some.
Improved safety.
Number 1 misconception.
A RUN capacitor IS NOT a START capacitor.
Why are some +5% & +6%. ?
i already know this
but no one believes me
Who were the 5 haters hitting the dislike.
The ones who thought they didn’t need advanced math when they grew up.
I was thinking the same thing. Either they are trolls or just unhappy people.
Want to know why Chinese capacitors fail. Take one apart.
Ooof so close. It charges and discharges 60 times per second. It simply doesn't store energy like we think of it in a DC system. It is used for shifting the phase angle in order to create a rotational force upon the rotor. I'm sure you know that but using the phrase "think of it as an energy storage device" is as erroneous as thinking it somehow changes voltage to any appreciable degree. Good video otherwise.
A capacitor is an energy storing device there is nothing wrong with that statement! Whether is connected to AC or DC voltage thisdoes not alter the fact that the capacitor is storing energy by the virtue of creating an electric field.
Capacitors are black magic. These are all lies haha
This is pure bs a 40v dc single cap fed by 5v when full will discharge 40 v wtfk r u talking about jffc such bullshit frfr
Could you kindly present a video on how to connect a external capacitor to an ac motor that does not have one. Can you just connect it to the power cord or does it have to be wired internally. Thanks !!