Capacitors are used in HVAC to help electrical motors to start and keep running smoothly.
They are low-cost components that come in multiple packages, shapes, and sizes.
What are Start Run Capacitors?
A Start capacitor helps a motor start to turn, while a Run capacitor helps it to operate more smoothly.
Motors used in HVAC, such as the condensing fan motors or blower fan motors, sometimes need help to start moving and to stay running at a steady pace, with no heavy up and down spikes.
To do this, HVAC units use what are called Start and Run capacitors which can add more amps or smooth out voltage spikes.
Start Capacitor vs. Run Capacitor?
- A Start Capacitor holds a charge to start a motor moving.
- A Run Capacitor keeps a motor running smoothly with no big up and down spikes.
Start Run capacitors are usually a single capacitor but can be separate
Not all motors will have a start or run capacitor; some can start and run by themselves.
Capacitors in HVAC can be separated with two capacitors or can be in a single package.
When they are separate, they are called “Single,” and when they are combined into one package, they are called “Dual Round.”
Example Dual Round HVAC Capacitor
Example Single HVAC Oval Capacitor
The Dual Round Capacitors are engineers trying to save on space and cost.
They could have put two separate capacitors in an HVAC unit but combined them into one package.
Example Dual Round HVAC Capacitor Wiring Diagram
A dual capacitor will have one leg to start the compressor (Labeled Herm) and another leg to start the condensing fan motor (Labeled Fan).
The third leg on a dual capacitor is a shared common leg (Labeled “C”).
How Do Capacitors Work In an HVAC System?
A Start or Run Capacitor can be combined into one capacitor called a Dual Capacitor with three leads but can be split between two separate capacitors.
The Start Capacitor gives a fan motor the torque it needs to start spinning then stops, while the Run capacitor stays on, giving the motor extra torque when needed.
If the Start Capacitor fails, the motor will most likely not turn on. If a Run capacitor goes bad, then a motor can turn on, but the running amperage will be higher than normal, causing the motor to run hot and have a short life expectancy.
After replacing a bad Condensing Fan Motor, a new Start Run Capacitor should always be installed.
A Dual Capacitor has three connections HERM, FAN, and COM.
If the unit has two capacitors, one is the Run Capacitor, and the other is the Start Capacitor. Keep in mind the compressor also often needs a capacitor which will be HERM (compressor).
How to Buy a New HVAC Capacitor
A new Capacitor should always be installed with a new motor. A capacitor can be bought at an HVAC supply company; there are usually at least a few even in a small town; also, online, Amazon or eBay is a good place to look.
Here are two common capacitors, the one on the left is a Dual Round Capacitor, while the one on the right is a Run Oval capacitor.
The Dual Capacitor is nothing more than two capacitors in the same housing, while the Run oval is a single capacitor, and an HVAC system will usually have two.
Capacitors are measured by the Microfarad, sometimes shown by the letters “uf” and Voltage. In any HVAC unit, the capacitor must match the motor.
The voltage can go higher if necessary but never lower, while the MFD (uf) should always be the same. In the picture, this is a Dual Run Capacitor and reads 55+5 MFD (uf) 440 VAC. The larger number 55 MFD is for the compressor, while the lower number 5 MFD (uf) is for the fan motor.
The lower number is always going to be for the fan motor. Then the voltage is 440 Volts AC.
(The + -5 after the MFD is how much it the capacitor tolerance is rated to go up or down.)
To order a replacement for this capacitor, it would be 55+5 MFD (uf) and 440 volts AC Dual Run Capacitor.
Example HVAC Dual Capacitor On Amazon
MAXRUN 55+5 MFD uf 370 or 440 Volt VAC Round Dual Run Capacitor for Air Conditioner or Heat Pump Condenser – 55/5 Microfarad Runs AC Motor and Fan – 5 Year Warranty
Testing an HVAC Capacitor
Testing an HVAC capacitor is done with an HVAC multi-meter; the multi-meter must be cable of reading the range that an HVAC capacitor can have. Many small electronic meters do not have this range.
Here I am using the Fieldpiece HS36 multi-meter with an Amp clamp.
This test is being done on a Dual Run Capacitor 55+5 MFD (uf). The multi-meter is on Farads, and the leads are on C and FAN (positive and negative do not matter). The lower number is for the fan motor, which is rated at 5 MFD (uf), and it reads 5.3 MFD (uf), so it is good. The leads C to Herm can also be read, which would be for the compressor.
To test a Run Oval Capacitor, simply touch the two leads. This one reads 4.5 MFD (uf) and is rated at 5 MFD (uf), so it is bad and needs replacing.
How To Replace a Start Run Capacitor
A new fan capacitor should always be installed when a new motor is installed. It is always a good idea to take a picture or write down wire coloring and connections.
- Turn off the power to the HVAC unit and verify it is off with a meter.
- Find the side panel where the electric is fed into the unit and remove the panel.
- Locate the Stat Run Capacitor, if it is a Dual Run capacitor there will be only one. If there is two then only the fan motor capacitor will need to be replaced.
- Verify the MFD and voltages, then connect the new connections from the old capacitor to the new capacitor one leg at a time to be sure the connections are correct.
(If you have two capacitors one is for the compressor and one is for the fan motor.)
Hi, I just replaced a bulging single phase run capacitor as a precautionary measure, but now only the fan comes on when the thermostat is asking for cool air. I suppose the new one could be bad, which I will check, but I’m wondering if it could also be the wiring. Unlike most of the examples I’ve read about, mine has what appears to be one red wire and three what look like yellow wires and there are no markings on top to let me know which terminal is for what. Could that mean that it doesn’t matter which terminal you connect each wire to? I thought I copied the way the old one was wired, but now I’m wondering if I did something wrong. Unfortunately, the diagram on the inside panel is un-readable. Please advise. Thanks!
Turns out the thick red wire connecting the compressor to the capacitor was not attached. Working perfectly now!
you shoudl look for the diagram online, it should show you the correct connections and their purpose. check model numbers, theyre usually on the outside stamped.
i have a condenser unit problem,the fan is not working but the compressor is,i changed the capacitor for the fan and started working for maybe a day but after that it stop again,,i check the new capacitor but it seems ok,,do you i need a replacement for the fan?how can i check if its already dead
I have to replace both the start and run capacitors. Problem: The (Hard Start Capacitor) was removed and thrown away, so I can’t go wire to wire. I do not have any instructions, directions, or a schematic. I can’t identify the exact Ac/heat unit I have because there is no outside label with model#. I have a number from the inside panel where the wiring is located and I have some numbers off the motor below the fan (compressor)? The run cap was still there so I can hook that up, but not the Hard start. This is a Coleman Mobile Home AC/Heat unit. Compressor H29B18UABCA OC 25
The run capacitor is a dual round (3 prong) the Hard Start Cap is 161-193/250
Does some one have a diagram or know how to hook up?
Where could I find a wire connection diagram and or model # of AC unit so I can get a schematic?
Today, the compressor in my Trane (outdoor A/C cabinet) quit coming on. The fan in the outdoor unit still runs.
The capacitor has an obvious bulge on the terminal end, and after removing it and testing, dual cap,
C to FAN and C to HERM both read 0 uF (yep, ZERO). And the capacitance meter is good – verified it on another capacitor.
How was the fan still reliably starting and running with a completely dead capacitor on the FAN? I would have expected that to make the fan not start up.
I have Goodman AC. Today, the fan was running but it was not blowing cold air. I had a backup run capacitor of the same ratings. I replaced it and the AC started to blow cold air. I tested the bad run cap with a good meter that had microfarad. The bad capacitor is rated for 70+5.0 MFD. I put connector to ‘C’ and ‘fan’, at it was at 5.31; I also put the connector to ‘herm’ and ‘c’ at it rated to 71.0. Now, I’m confused, did I really have a bad capacitor?. After I replaced the capacitor, the condenser would turn on until I set the thermostat to 50 degrees. Once the condenser turned on, I set it back to 77 degrees and I’m good now but I want to understand what got my AC going again, any information will be greatly appreciated.
Hi there, how do I identify which terminal is which on a new capacitor?? I have purchased a new capacitor for my air conditioning unit… the problem I have is that the new capacitor has no markings and no way of telling which terminal does what.
It is a moulded plastic type one with four terminals individually sticking up from the top.
The old one is metal and the terminals although there are still four, there is two pairs.
any help would be appreciated.
I had a power failure at home and the breaker tripped blowing the dual round capacitor. I replaced and the 5 ton central ac is cooling great again, but the system is turning off and on every 2-3 minutes. What can cause that? I turned the unit off to avoid high electricity cost and I’m not sure it will damage anything.
I have a 40/5 uf 370 volt capacitor currently installed in my heat pump. Is there any advantage to installing a 55/5 uf 370 volt. Or a 40/5 uf 440 volt capacitors or a 45/7.5.
My HVAC unit has 2 capacitors in it. A dual capacitor with 3 terminals 40 + 5 uf 440 VAC, and a smaller run capacitor with 2 terminals 88-108 uf 330 VAC. What is the purpose of the second capacitor with 2 terminals? I thought the dual capacitor took care of starting and running the fan? Should I just replace both capacitors then as my fan won’t start running and runs very slowly if I give it a nudge. Thanks
The second cap with 2 terminals is a start capacitor, not a run capacitor. Is it a black round cap with a resistor across it? The dual capacitor is for running two motors: the compressor and the fan motors.
Can I ask some question, because I am not very sure?
What happen if hvac air compressor start wire is connected to the Fan terminal of capacitor? or connected to the large then system require herm terminal of capacitor (ex: system need 35 uf, but connect to 60uf)?
I think air compressor will try start it but it can not start it since low uf on fan terminal of capacitor then maybe burnout winding at case start wire is connected to the Fan terminal of capacitor.
on other case that air compressor will start it but it will take long time to burnout winding compare to case 1 since it just overload on start phase.
I capacitor job is to hold add a extra line of power ( making single phase to 3 ph. the uf changes the line voltage to the unit to hold the speed the motor is running. / a start cap is just a kick start and drop out or is remove itself after unit starts to run. you can see the amp draw with the 35uf and the amp draw 60uf is different due to the voltage across the run cap. common to fan or hemp .
I have Tempstar 12 -model NAC260AKC3. I lost Capacitor and want to buy new one. I can find fan label is 5.0 mfd/370 vac. Compressor only shows 1 PH, RLA 25.0, LRA 148. Anybody knows what is Capacitor I should buy? such as 80/5 370, 50/5 370 or any combination?
Hello, just replaced my capacitor. But — When the condenser unit was first turned on the fan ran clockwise – in the right direction. But when the high speed kicked in the fan motor came to a stop then started to reverse direction. When the low speed kicked back in the fan motor came to a complete stop until the high speed kicked back in then it started turning in reverse again. Not sure, but maybe when the compressor starts the fan reverses too.
What’s going on? Bad Cap? Mis-wired?
New motor is in programming mode so when it is turning the right direction and speed remove the programming cord and install the proper hardware came with?
How do I jump from a dual start capacitor to a just run only a capacitor for a blower motor
Can i use this -Dual Run- RoToM 80/5 MFD 440/370v, 3 prong capacitor, to start a lawn tractor? Or are they only for AC application’s? Its all jibberish to me!!! I can’t even figure out which wire would go to what! C-Fan-Herm?
Hello, my Lennox air conditioner calls for a 60+7.5 capacitors. My outside unit had 2 capacitors in it (a dual capacitor with 3 terminals and a smaller run capacitor with 2 terminals). My father-in-law replaced it my broken dual capacitor with a 80uf start capacitor (2 terminals) but I’m worried about the uf being too high and affecting my compressor.
So I bought a new 60+7.5 dual cap and was going to replace the 80uf start cap and leave in the small capacitor. My question is about the wiring. There’s a red jumper wire that currently goes from the large capacitor to the smaller capacitor. Should I connect that jumper wire to (F)an or (C)ommon on the dual capacitor? The other 2 wires are a red (C)ommon wire that goes to the contactor and a yellow wire to the (H)erm. Thanks for your help.
to clarify, my system wants a 60+10 so i guess that’s why the installer used a 2nd smaller capacitor since the 10 is a little rare for dual capacitors. How should i wire the jumper cable between the 2 capacitors? Thanks.
I recently replaced both start & run capacitors on a 10 year old Trane unit.
The new capacitors, although rated the same as the old capacitors, are much smaller in overall size.
Is this size difference common?
Our AC unit stopped working, we had a tech that came out that said we needed to replace the Capacitor.
The original Capacitor is “CBB65B 40/5 uf +5% 440 VAC 50/60Hz 40/70/21”
We replaced it with a Capacitor from Amazon “40/5 MFD ±6% SH CBB65 -40 to 70 370V/450 VAC” – this Capactor literally exploded within an hour of installing it.
We ordered a different Capacitor off Amazon ” 40+5 MFD 40/5 uF ±5% 370VAC/440 VAC 20/70/21″ this one lasted 2 days, the AC isn’t working. I’m 90% sure the wires were connected properly. Brown to Fan, Yellow to Herm Purple/Red to Common
Not sure what else to do, and can’t get the original part.
The Tech wants $400 for the replacement Capacitor
What am I missing?
Hi. I’m sure you’ve probably resolved the issue by now, but if it happens again, I would replace the relay as well. Sometimes they are the true issue.
I’ve replaced my motor run capacitor three times in the last 4 weeks. A new capacitor always resolves the problem. Does frequent failure indicate that something else is wrong? I was careful to replace the same capacitor specs. The Paradigm Geothermal unit is 16 years old.
I have a single capacitor 40 MFD on my Rheem. Both condenser and fan motor are connected to it. Fan motor is shot. Replacing fan motor and getting new dual capacitor. Is capacitance halved as it is currently wired? 20 MFD to compressor, 20 MFD to fan? New fan is 3 MFD. How do I know compressor capacitance?
Do I need to discharge a dual-run capacitor before removing it according to instructions above?
No, you need to ensure the power is pulled at the disconnect at the whip the gray small box.
Need direction! Old Carrier AC has dual round 40+12. Does no one make them anymore? And would a 40+10 have a snowball’s chance of getting the fan spinning if rated for 12?
You can split them up and make them singles if you cant find the dual round.
My fan motor stopped spinning. I was able to push start the fan with a stick, but even I got the fan spinning the compressor is still not working. I understand that the power stored in the capacitor/fan is low so the fan motor doesn’t kick off. so does the same concept apply to the compressor as well? coz the power in the herm cell is low so the compressor won’t start? Am sorry if this concept sounds funny to you. Am still trying figure out how this works.
If the fan started after that the capacitor is most likely bad. You may also one to check your L1 and L2 load and non load side to ensure you have the necessary power if not it could lead you to believe its the problem.
Ensure the ground and all connections are snug.
Correction to my comment, I was going from memory.
It’s 1xBrown to fan from the Outdoor Fan Motor, 1xOrange from OFM to common, 1xOrange from compressor contactor to common, 1xPurple from Compressor to Herm. It turns out, while I was outside looking over the diagram again, the compressor sprung to life. I guess it just took a few minutes.
Fan still won’t spin… Well, it’ll spin freely when it’s off and tries to spin when it’s on but it’s as if it’s stuck. Guess it’s time to order a new fan motor. *sigh*
Okay, so I’ve got a Weatherking unit and the compressor would buzz but the fan wouldn’t turn. Called a professional, he spun the fan manually to “kick start” it and the fan worked, so he told me it was likely the ‘start’ capacitor in the round dual run unit. He called into his office for something and came back to tell me that he would not be able to do a single thing more without my authorization because it turned out I only had a 5 year warranty and not a 10 year as I thought I had so I’d actually have to pay for the capacitor replacement… At $300 labor. He pulled me aside and told me “Look, this part is less than $50 and takes only a few minutes to install” when I explained to him that I can’t afford $300.
Well here’s where I’m an idiot: I forgot to take pictures of how the old one was wired when I discharged it and removed it to have something to show the folks at Home Depot when I went to buy a new one. The panel I remove to get to the capacitor is ZERO help because it shows an oval single run, and there’s only a space for a round dual run like the one I took out so when I wired it by the diagram on the panel of 2xOrange to fan, 1xBrown to Herm, and 1xPurple to common, the compressor no longer buzzes and the thermostat doesn’t “click” when switched to cool.
What wiring configuration should I be using for a Weatherking 13JPL and does it matter which of the posts on the Herm, Fan, and Com terminals I connect the wires to?
Can I go from a dual cap to a single cap? If so, how do I wire it in?
Can a capacitor emit an odor when it goes bad? This past weekend we had a terrible odor coming through the HVAC system all of a sudden in the middle of the night. The system continued to run fine, cool the house, and had no unusual noises. I had two different HVAC technicians check the system. The first wanted to change the blower motor and the second tested and replaced the capacitor for the blower motor. We have been running the system since then with no apparent odors now. I am holding off on replacing the blower motor at this time. But can a bad capacitor emit an odor like that? We have ruled out any dead animals, etc. And the smell is not really a burnt smell or burned plastic or wiring. Thanks!
A capacitor does not emit any odor, other than performing an electrical diagnosis the only indicators that it might be bad is swelling, extreme wear (rust/corrosion/etc.).
There are 3 things that could cause a smell from the system itself. 1 the worst situation possible a compressor burning out or burn out, an electrical motor either pcm or ecm and another bad scenario a fried control board.
I am replacing a dual compacitor but thought the picture I took included the wire configuration. The only one I remember is yellow to fan. How do I know what a compressor looks like?
The compressor requires a higher current to start, the fan lower. The outdoor fan should be in the ball park of 5 mf and the higher one wires to the compressor. If your not sure trace the wires, common always goes with common.
What do you think about suggestions I’ve heard to replace the run capacitor as part of preventive maintenance, on a two-year basis? If someone doesn’t have the necessary multimeter to check capacitance and if deterioration but not failure of the capacitor is predictable and will still permit the equipment to run but with slower fan and compressor speed, less efficiency and greater wear, this would seem a good idea. I have two systems and when one run capacitor failed five years ago I replaced them in both units with no problems since. However, during a friendly chat with an a/c tech who was installing a new system for a neighbor, he suggested they be replaced routinely and on a bi-annual basis, and I’ve read that elsewhere as well. Please comment; thanks.
It’s not a bad idea, but it may not be required. You should test the capacitor with your the leads connected. To see if it’s still running with in design specifications. Normally the tolerance is posted on the capacitor data tag. Something to the affect +/- 6% of its rated mfd.
This is a very informative website regarding the testing and replacing of a HVAC capacitor. I was surprised though that no one has asked how to properly discharge a capacitor. Can’t one receive a dangerous electrical shock if a capacitor is not discharged before executing the various tests? If so, what is the procedure for safely discharging a capacitor?
Gary to answer your question about safely discharging your capacitor, take a screw driver with an insulated handle (plastic with rubber) and lay it across both terminals on a single oval, and from C to fan, then C to HERM on a dual round. Or my personal favorite, just touch all the terminals to the casing (sheet metal) on the unit.
My fan motor locked up and I’m replacing it. The new motor has different colored wires but the same wiring diagram (one wire hooked to line voltage, one hooked to the relay, and two wires connected to a single capacitor). My old set up had one wire connected to the common contact on a dual capacitor with a wire going to the compressor and the fan contact empty. The other wire went to a smaller single capacitor and the other contact on this capacitor was connected to line voltage coming in. This seems incorrect to me but I know it worked so I was going to wire it back up the same way. Only problem is I’m not sure which wire I should connect to the small capacitor and which one to use to supply voltage to the compressor capacitor?
Yes. A higher number on voltage 440 versus 370 is okay. The capacitor will last longer if you use the 440 and it only is specified for 370. Having 50uf when it is designed for 40uf going into the compressor means your compressor will be getting too much electricity and the life of the compressor will be shortened. The 5uf is for the fan. Try Airstar supply for an exact original design spec capacitor. Good luck.
I installed a new 88uF hot start cap (single, 2 prong,) to a older (18+yrs) York 3 ton condensing unit, cleaned (filed) contactor, and pushed the contactor in to start the fan/compressor, they started and the new start cap blew! Blew out the little safety plug and was bubbling for a moment…immediately killed power. I wired it same as before. What could cause this phenomenon? Help
Your very lucky. You need to use a relay circuit when wiring in the hard start?
Is it weird that my ancient looking ICP HVAC unit does not have a fan wire connected to the Dual run capacitor? It has two large wires connected to the common, and 1 small grey wire connected to the HERM, but no wires connected to the Fan.
It also has a single capacitor that is separate.
I have a RUUD AC model #RA1648AJ1NA (4 ton). I bought a 5-2-1 compressor saver (hard start) kit. Opening up my condenser unit I see only one single 45mf capacitor. It appears to be connected to the compressor. I have seen online somewhere that some fans (OFM) do not need a capacitor to start and run. I assume I would follow the wiring diagram for a 2 pole run capacitor. Correct?
I see a red wire coming off the contactor to one side of the capacitor and the other side runs back to the compressor (which I assume is the start side of the compressor). Since the capacitor is 45mf (a fan cap would be much less) and one wire leads back to the compressor, then it should be the start capacitor for the compressor.
Am I seeing this correctly?
I Changed the single capacitor by dual capacitor.there is HERM,FAN.C.i gave the connection to FAN and C but fan was not run ,i need to rotate by hand,If once i rotate then automatically Run Continuously. starting is problem .So please give the your suggestion.
Amana a/c unit, condenser fan bad, changed out and changed the recommended capacitor for it, however, it went from a 3 port to a 2 port capacitor. Not sure how to wire it up. 2 yellow wires, together on old and a red wire on another port. 1 wire to condenser motor and 2 wires to fan motor. Now the start cap is hot and leaking. Need help on how to wire from a 3 port to a 2 port capacitor. Will replace the start cap tomorrow.
My Compressor fan motor was overheating. I changed it out. The new motor would have to be handstarted. So I changed out the capacitor. So now I have a new fan motor and a new capacitor with the correct ratings. It still needs to be handstarted. Any solutions?
Check your connections, if they are bad a high resistance connection could cause this issue. Recrimp with new contacts to be sure. Check your voltages, making sure you are getting 240 v to fan motor
I accidentally touched the common on the capacitor and lost all my power does this mean the contractor went bad? My inside air handler is running but the outside one doesn’t show any volts in my contactor.
circuit breaker… ?
Check the fuse on the board in the evaporator unit. I’ve done this before and there is a fuse in the inside unit behind the service panel of the fournace/evap unit inside the house that blew and that needs to be replaced. It looks like a car fuse. You can look through the transparent plastic window on the fuse to see if it’s blown.
Hi, the hvac tech stopped by and did the annual check on the air conditioner; the compressor capacitor has a normal operating range of 42.75 to 47.25; the unit tested at 41 mfd.
is this far enough outside the acceptable range that it should be replaced now…or can it last longer?
My husband recently changed out the disconnect because the breaker kept tripping but now the ac runs slow to cool the house. Could that be the capacitor needing to be replaced?
First thing I would do is check the voltage before and after the disconnect.
Can a locked compressor severely damage a run capacitor?
One side of capacitor is melted along with adjoining wires. The other terminal looks OK. Capacitor has leaked into the control cabinet. Area above capacitor is charred.
a capacitor is like a basket holding eggs except this basket holds electrons. If youe compressor is locked rotor it should be off on high amps. In other words the internal high amp cut out will be engaged and therefore no electricity / electrons should be engaged at the capacitor. whenever replacing a compressor new capacitors shoulf be installed regardless if the old ones test ok. so the answer is no.
I need to replace my round dual capacitor. The new one is well marked with C, HERM AND FAN. The old one has a MARS label but is made by Airstar. Believe it or not, it has no markings for the three contacts. One has two, one has three and one has four push-on contacts so I assume that Airstar has some secret code as to which is C, which is Fan and which is Herm, but they sure aren’t telling anyone that I can find. What a stupid oversight, or so it seems to me. One of the two condensers in it is open contact (failure) or else I could figure out which was Common. Does anyone have any idea what the secret code is?
Best bet is to do a search for the schematic for your unit. it will provide the color code of the wires used in it. It It is often found on the inside of the electrical box cover. Other option is to trace the wires. Before you remove the wires make a drawing of the connections, color coded wires, and label them which A, B, or C terminal they are on. To find whic terminal is what, the fan terminal will have a wire connected to the fan motor, and then the common terminal is going to be connected to the start relay. Also there may be two “hard start capacitors” (which are capacitors in series with a relay to add capacitance for a few seconds to get the motor turning and they look like a capacitor with a plastic cap and have two leads comming out of the top) in the circuit that are add ons and will not show up in the schematic.
Can you trace the wires back? One is going to the condenser fan, that one is just one wire all by itself .
The common one should goto the Main contactor’s de-energized side. that same common also goes to the condenser fan, and another may go to the positive temp coef. resistor.
Finally the herm may have two wires… going to the Comp., and the other side of the Positive temp coef resister.
You should get a schematic to see for yourself. I can goto Google and get most ANY schematics for Air nits.
Least tabs is fan, middle is herm/compressor, most tabs is common/line voltage off of the contactor.
Common terminal on capacitor & common wire from compressor…
Why is it that the R (run) wire from the compressor goes to the common terminal on the capacitor? I would think the common wire on the compressor would go to the common terminal on the capacitor? I looking an an RV rooftop air conditioner, 120v.
This is one of the most confusing aspects of HVAC circuits. I know this because I am a student studying HVAC and anyway here is how it’s been explained to me. The C terminal on a dual capacitor is not referring to neutral and does not connect to nuetral. The C refers to common, but in this case it’s a common FEED – in other words, it connects to a common power supply. So, if you notice, most air conditioning wiring diagrams have power feeding off of the T1 terminal of the contactor and then power is fed 1. to the compressor; 2. to the condensor fan; and, 3. to the c-terminal of the dual run capacitor. So, it’s the contactor actually powering up this capacitor, and the way it’s charged is from current flowing from T2 at the contactor, to the c-terminal on the capacitor. Every time voltage cycles, the capacitor is repeatedly charged, and then it’s discharged. When the capacitor discharges, the current flows from the capacitor’s H termina to the compressor’s run terminal, and also at the same time there is power being discharged from the other capacitor terminal (the one that’s labeled fan) and power flows from that fan terminal to the run terminal on the outdoor fan. I’m only 2 months into the training, so I hope I have this concept clearly understood. Otherwise, please let me know in an email.
My a/c was not working, the last time the repair man can out all he did was re-connect the dual run capacitor and then next year we tried using the a/c but it just wasn’t getting cold, sounded like the fan was only coming one.
We got a new dual run capacitor and we installed the new one and the a/c was back to blowing cool air, until like a week after it was installed. Can the high heat be a factor in the a/c not blowing cool no more? Or do I need a higher voltage if they have it? PS it was the same exact capacitor
Help me pleaseeeee
If you replaced the capacitor with the same exact one then that is all set. Your contactor may be at fault, does the fan run and do you hear the AC condensor running which sounds like a large refrigerator.. I had a similar problem and it turned out to be the contactor was bad and working only intermittently.
I just replaced a dual start/ run capacitor on my a/c. It had stopped working. It had been in my unit for 10 plus years.
It was labeled 50 + 5 uF 370/440 VAC. I replaced it with the exact model and everything works smoothly.
However, I just found out that the original part spec from the a/c manufacture was 40 + 5 uF. Should I change back to the original specs?
It should match the compressor and condensing fan motor.
My a/c unit’s fan capacitor has gone out (visually inspected it), and the capacitor on my compressor is a dual cap. I (mistakenly) ordered a new 40/5 dual cap, and I was wondering if it’s possible to move from having separate cops to using just the dual cap.
Yeah, I know what the dual run is.. The smaller 5 uf cap has (obviously) with wires coming from it.. Would I just have to run those wires down to the dual run? Or would there be other wiring I would have to adjust?
Meant to say it has 2 wires coming from it.. They both go back up into the fan motor
Maybe we Gordon people how to discharge a capacitor and to treat every capacitor as a live capacitor before you have people handling a 440 volt AC capacitor with their bare hands
Mine’s well just hand them Smith & Wesson or Glock 45 and tell them to point it at their faces and hope for the best. Capacitors are no joke and can kill anybody instantly if not properly discharged or handled
They would only do it once
Great article!! I’m trying to replace a dual capacitor on my HVAC, but can’t find the exact part# replacement. I’ve found one with the exact same specs (30/7.5 MFD, 440V, size) on Amazon. Are there any other specs I should compare before using as a replacement part? I’m a bit wary because there appears to be a sizable cost difference (available, new part number is $15, backordered, original part number is $40). I’m thinking perhaps the cost difference is just due to supply/demand, and not some other factor.
Original part#: D147086P33 (CPT00692)
Possible Replacement: P291-3074R
Just make sure the electrical specs are the same. The only real issue you might run into is if it’s too large to physically fit into the location intended.
Thanks for the info. I just replaced my capacitor with one similar (3uf 370vac) to the original. The fan motor will still not start on its own ( i have also replaced the fan with similar to original). The fan runs fine when i kickstart it, but will not start on its own. So i possible need a higher microfad rated capacitor? The fan paperwork shows the 3/370, but still not starting. Suggestions appreciated! Thanks, Eric
Mine had two capacitors. A run capacitor with a single number uF, and a start/run capacitor with two numbers (45 uf/5 uf). That is the one that needed to be replaced. They were located in seperate panels which made it confusing at first.
Motor on my rv a/c spins freely when off but hard to turn with power on ? Motor or capacitor ? And also I removed the old capacitors.. They looked pretty bad rusted and dented .. Tops are rusted so bad you can’t read which terminal is which.. Any way to tell ?
The motor could have seized due to not being used for a great time. You should try to spin it while on if it fails to start. Another thing to consider is that if your system is nearing the end of its shelf life hesitatant starts are normal. One way to prolong the inevitable and that would be cost effective versus purchasing a new system would be to install a hard start kit. It will give it that extra ump to get going.
Rust on the blades is bad and should be cleaned off gently with a brush. Infiltration greatly affects your in door air quality.
Rust on the capacitors is ok as long as they past an electrical mfd test and show no sign of leaking.
A few days ago a tech came installed a new dual run cap on my heat pump. It has a label showing 40+5 uF, +-5%, 440/370VAC/B. Could you explain to me what 440/370VAC/B means? Also, the old one has 40+4uF, +-5%, and 440V on it. Is the new one oversized a bit for the fan motor (5uf vs 4 uf)? Is it alright for this replacement?
Many thanks for your help!
The 370VAC is (volts alternating current) stating you can not send any more than 370 volts into this capacitor or it will fail. Most residential houses have less that 240 volts going into their AC systems. so that part is ok.
Hello, I have a Bryant AC unit model # 698BNX036000ABAA and I saw the compressor capacitor is bulging and I want to replace it. The current capacitor is 45 uF, 370VAC, 50/60 Hz but I cannot find out online if this is the correct specs for the capacitor or if someone installed the wrong capacitor for this unit and that is why it has gone bad.
It’s likely you just have a defective capacitor . These capacitors do go bad and need replacing so it isn’t uncommon to find what you’ve described. If I were you I would just purchase a new capacitor with the same ratings More than likely this will solve your problem. I just finished replacing the same capacitor and contactor on my ICP/Heil HVAC now it’s running fine.
If a unit is at least several years old replacing contactor switch is also recommended. In my case unit is 13 years old and contactor switch points were charred.
capacitors normally go out every 5 years or so. 45MFD is what I mostly see on units. Call Bryant Manufacturing tech support they will tell you exactly what capacitor belongs in your condenser
My fan went out on a Goodman 5 ton all in one I went out and heard the compressor running and before I cut the power to it it shut it self off. The squirrel fan was still running till I killed the power. I fixed fan turned breakers back on and nothing it’s like it is dead could this be the run capacitor any help would be great. Thanks
Hello, I have a question in regard to my Lennox AC unit model # 10ACB42-5P. It has 2 capacitors, a Start , and a Run. My start capacitor had been leaking, so I removed it and purchased new one. The wires going to it are both red, but pulling them off, I didn’t pay attention to whether it made a difference how connected. Thus, need to know where to reconnect red wires to the start capacitor?
If it is an AC capacitor, it will not be polarized, so there is no (+) or (-). If it is a dual cap with three terminals you need to know which is Common, Fan, and HERM.
An HVAC contractor came out and replaced a dual capacitor (60/10). He did not have a dual capacity so he installed two capacitors in its place. He said this would work as good as the original. If he replaced with a 60 and a 10 is that true? Should I order the original dual 60/10 and install myself or not worry about it? Thanks
Should be Fine… as long as they are mounted securely.
Follow the wires, the one going to the the fan motor will go to FAN. the one going to the compressor will be labeled HERM. The one labeled C is the common wires for both.
I have the same problem. There was a red and purple wire attached to one terminal, a red wire to another terminal, and an orange wire attached to the third. But I counldnt red the top bc of rust which was C, HERM, and which was FAN. Any idea? Couldn’t really trace wires back and schematics are to hard to follow. Any help?
Great write up! Two quick questions if I may:
1) What material is the outside of a dual run cap? (Where the strap goes around) My Cap has rust on top but nothing on the side.
2) I’ve seen videos where the new replacement cap is small in diameter than the one being replaced. To compensate for the strap that holds the cap in, they removed the strap and used plumbing strapping(on a roll). This strapping is galvanized. Would this cause a galvanic action between the cap and the strap where they make contact?
what is your solution to a new cap with a smaller diameter than the one being replaced in relation to how you compensate for attaching the holding strap?
I am an amateur but what I did was shorten the strap. I took exceptional care that the strap would not press down too hard or too soft on the capacitor. I think its oval shape made it easier than if it had been around one. It took several (>10) minutes to do this and get it to a point where I thought the pressure was “just right”.
Well my condenser fan motor stopped working and just would hum and get hot. I was told it went out so i bought a replacement a aftermarket with the 4 wire ,and the direction wires and a ground wire.and it came with a run capacitor . I installed the fan motor and connected the brwn and brwn/wht wires to the capacitor that it came with. When I turn on the a/c system now it dont get cold, but the fan works now. Before the fan went out it would blow cold. So now im thinking the original 2 stage capacitor is my problem from the start.
What do you think some feed back would be appreciated. Thank you.
Everyone needs to research and troupleshoot if ur not rseaching ur specs for your motors and capacitor then leave it alone
I have a 3-year old Bryant furnace With a blower that makes humming noise but does not turn. I believe it has a bad capacitor but I can’t locate it anywhere near the blower. Is it possible my furnace doesn’t have a capacitor? If so, how do I jump start the blower? My combo AC unit is located outside. The fan outside works properly.
should have one… check for loose wires; and ground wires…if you give motor fan a “push’ and it gets going … the motor should not be going bad so early…replace capacitor… check high limit switch on furnace?
What causes compressor capacitor (single) to fail 5 times in 9 years? 45 uF 440 v. 1.5 tons Rheem minisplit. I have 3 of the exact same units. One never failed, one failed 2x and the 3rd 5x., this gets the most use. The units have fan caps – seems not nearly as much a problem.
Hello, I looking for some advice. I just ordered on Amazon a dual run capacitor rated MFD 25/5 (as a back up) but when I test it with a multimeter it reads MFD 23/4. Is this defective and need to be exchanged or is this within tolerance?
Could be tolerance of the capacitor or tolerance of your meter. Either way I think you are fine.
Stay with me because I’ve done hours of research and my specific problem doesn’t seem to be addressed. In April I replaced my York condenser fan, blade and both capacitors (and it has worked fine until now. It is over 108 in Texas right now and the other day I was told our A/C was not cooling well. When I got home from work the condenser fan was running backwards and since it was later in the day it was cooling better. The next morning I checked again and the fan was running correctly, blowing air out the top. When I got home I was told it wasn’t cooling well again so I went outside and it was running properly so I thought I would rinse the coils. After putting water on the coils some of the water contacts the fan and it immediately reversed and began sucking air in the top. I have checked the capacitors and they all read within specs. I even tried reinstalling the old capacitors (which also read in specs +- 5%. No help, still running backwards. As far as I can tell it is wired correctly. Just a minute ago I went out and the fan was slowly spinning backwards. Killed the power and waited a few minutes. Running backwards again. I’m beginning to think I need to call a Priest instead of an HVAC tech. Thanks for your reply.
Sounds like you have the wires backwards on the capacitor double check the common and fan wires. C isn’t compressor it’s common it comes from the contactor.
You installed the blades upside down
will wrapping electrical tape around my a/c dual capacitor cause it to overheat and fail ??
The roofing company covered my a/c unit with a tarp while it was running and the unit stopped working. I contacted a repair man and he said the capacitor burned out and replaced it. Question: Can the high heat outside and the lack of ventilation cause the capacitor to overheat and burn out or it this just a coincidence ?
Covering a condensing unit while its running in cool mode will raise head pressure and cause your compressor to go off on thermal overload… It woo n necessarily take out your capacitor but it is possible with the increased load and higher amp draw
Does it matter where you connect the brown and brown with white stripe wires on the smaller oval capacitor?
can u tell me waht is H,F,C capacitor terminal.
C – Common
F – Fan
H – Herm (Hermetically Sealed Compressor)
my Ac stopped blowing cold air. When I called my home warranty company they sent someone out and came to the conclusion that frogs got on the Capacitor caused a short and locked up my compressor. Does this sound like something that could happen.
Happens all the time
My condensing fan motor starts fine but after 10 to 15 min it shuts off. Compresser stays running but fan motor stops. I have 2 capacitors in my unit but fan is not connected to large round capacitor. Only the compressor and common utilized on large cap. Could my issue be the run cap that the motor is connected to or could there be another issue I should look into? Please help!
Could be capacitor, could be bad fan motor… if you have a low ambient kit, sometimes it will cycle the condensor fan motor on and off to keep the pressures in a certain range
Is there risk to hooking up the brown/white wire to a dual run capacitor? I just replaced the fan motor and capacitor, the original motor had 3 wires the new 4. The wiring diagram said to hook it up to the common lead on the capacitor. So I did. Will it cause ether fan to overspend and/or any damage? Do I remove it or is it safe to leave it.
Yes this is this is a died short . White is common to make a 4 wire motor into a 3 wire connect brown/white (common)to the white (common) these two or the same wire.
I am having a problem understanding the duel round capacitor. Is it just a starting capacitor for the compressor and fan motor, or is it a run capacitor for the compressor and fan? Or is it both? I always hear people calling it a dual run capacitor, that is where the confusion comes in. Thank you
It is a dual run capacitor
My understanding is a dual capacitor is sometimes referred to as a “dual round”, so that may be the source of the confusion. A dual round capacitor will include two capacitors, combined in one “package”. Most single capacitors are an oval shape. Single capacitors will usually (always?) have two male connectors (at least the ones commonly used in HVACs); whereas the dual capacitors three male connectors, one of which will be a common connection.
Hi , Great site, My ac seems to be working but just not cooling as it should could it be the capacitor?
whenever i look at these hvac videos they say they are changing the start run capacitor. yet it always seems that they are changing the dual capacitor, compressor, fan.. am i missing something? i have yet to see one video of someone changing a run capacitor. how does the start capacitor turn off, i never see anything in the schematics,, also, are those dual capacitors start capacitors ?
my existing capacitor was 45 +5 but by mistake I installed 70 + 10 capacitor , I noticed the fan was spinning too fast > after 5 -10 min of running , I stopped it and replaced with old capacitors
would this have caused damage to compressor already ?
The fan is running normally but I am worried about compressor
I am replacing the existing 4 wire condenser fan ( purple, purple, black, orange) with a new 3 wire (purple, orange, and black) condenser fan. Currently I have 3 capacitors wired to the condenser unit outside. How do I wire this new fan? I read that I need an extra jumper wire from contactor to the run capacitor? Then purple wire from fan goes to other side of capacitor?
In my town I could not find the required 70/5 440 dual capacitor. Will my unit be in trouble if I use a 60/5 440 for rwo days which is when Amazon will deliver my 70/5 440 capacitor. Also, what will happen if I use the 60/5 440 capacitor?
For 2 days might not be bad in an emergency situation. It was cause your system to draw more power than needed and the equipment we work harder to meet the demand. It’s important to pay close attention to your run load amps and lock out rotor amps which you will fine on the data template on the machine. (LRA/RLA) If your within the designer engineered specifications you should be ok for 2 days other than a small spike in your power bill or a occasional light dim or flicker when the system starts or stops.
I had an AC guy fix my unit about 5 years ago and it turns out I needed the fan motor and capacitor replaced. My fan it not turning on now again, so I thought I’d try to have a look. My unit requires a 30+5, but when looking in there, a 45+5 is used, but only one side of the dual capacitor is connected and then there is a separate single 5 uF capacitor in there. Why would he not have just used both sides of the dual capacitor? Why is the capacity higher? Maybe the fan motor he replaced it with required a higher one? Difficult to know how to fix when he did not just stick with OEM.
The technician on your job site did not have the correct capacitor and installed the closest thing he had to be done with the job in one visit. A lot of A/C techs are not very good at what they do … and many who are good at what they do are not quite ethical at times. It’s good to know the basics.
Nothing wrong with what he did electrically, just made what he had work.
A/C fan and condenser stopped working. I suspect Contacter. I ordered the part. But when I opened the A/C I noticed there was a wire not attached. The single capacitor looked like it was hooked up tight to the fan motor. But tracing the Disconnected wire deeper inside was a dual capacitor in which the Herm looked intact to it, but the loose wire was connected to the fan part of the dual capacitor. Could it be the fan motor was working working off two capacitors and I accidentally disconnected one? If so, where do I connect it to? The contactor? Which side?
he wanted to charge you for the parts and labor. maybe the one side tested bad. I doubt it.
Clyde, who is “he”? I am the one trying to put this thing together. I got the contacter yesterday. I am trying to figure out where this loose wire is suppose to go.
My AC fan would not come on , so r eplaced a dual run capacitor today., for The fan started right away, but after15 to 20 min I noticed the thermostat didn’t lower. The fan stopped again. Also, I ordered the part from Amazon by the numbers on the capacitor, and the new one is is 2 inches shorter than original.
any suggestions, in the middle of a heat wave .
I’m going to sound like an idiot here, I’m aware when you replace anything you go by the previous specs to replace it with, but I was kind of thrown a random “test” so to speak where I had to match the right capacitor to the right motor, how exactly would you go about doing that?
Our AC stopped working yesterday and after a few calls we got someone to after 5. The service call was $110 for after hrs., I’m fine with that, but the tech told us we need a new unit that our compressor was shot. Then he said he could “hard start it” to get us through temporarily. The only thing he changed was the run/start capacitor shown here. Which I think I understand is not a “hard start kit” that can be used to bypass something, I don’t know. Anyhow he charged us $330 to replace the run start cap and because I’m pretty sure he didn’t have the right one on the truck, sold me a song and dance about how a 55/5 cap would give our dying compressor the jolt it needed to start over the 45/5 that was in it. Just talked to another company and they said they do sometimes do that. The OG also said that the amps the compressor was pulling 12 something should be 7 something.
A jump start or hard start kit needs to be used and wired into the capacitor. That’s was a temporary modification. A modification that was outside the engineering and manufacture design which could harm your system by causing excessive over amping. A jump start kits does provide extra power but only for a brief second. A safety is wired into the circuit that cuts off the extra power being feed to the system once its demands are met. A capacitor does not hints over amping. It would be like flooding a gas engine.
He ripped you off, sorry to hear that. There are a lot of dishonest people in the field. It’s also a secret hvac code not to bad mouth other techs so another tech or company may not be inclined to point you in the correct direction.
i have a 4 wire 380v fan that reads
:380v 50Hz 350w
:B IP44 S1
color codes for wires Blue,black ,brown & yellow ,my main worry is what can be the (uf)capacitance of it if connected to single phase because i cant figure out how it can be opened to apply delta or Y series pliz help coz i have a 220 power supply @ home
Thanks for the Ebay link. From what I’ve seen, APRStore.com offers a nice sizing chart for HVAC capacitors and furnace capacitors. Most of the capacitors I’ve looked at are $5 to $15 dollars, so a little less than Home Depot and Lowes.
Replacement is really easy, but be sure to watch a youtube video on how to replace it.
Stay safe and hire a professional if you feel unsure about doing it yourself!
Hello, I have an Armstrong unit and I believe I need a new capacitor. The past two days I’ve been jump starting it but now it doesn’t spin at all. The unit works otherwise but just no cold air. So the existing capacitor specs are 55+7.5 MDF and 370 VAC 50/60 HZ. I looked up my unit and the specs are 45+5 MDF 440 VAC. This is a new home to me and first summer. I’d prefer to use what the manufacturer states than to match what is currently there now. I’m going to buy both but unfortunately the proper one will not arrive until late next week and other tomorrow or next day. Hopefully I will hear back from someone prior to installation and appreciate any and all advice. Thanks!
Can i use two capacitors in place of one capacitor in a cooler motor to increase the speed of cooler ?
I want to replace a dual 55/15 uf with a 55/5 uf and a 15 uf. On what terminal do I connect the jumper wires and to what terminal and which capacitors do I connect the three wires that were connected to the Common terminal on the original 55/15 uf capacitor.
Im sure you figured it out by now but the common wire will need to be jumped from your dual to the single and the fan wire will need to connect to the 15 and the compressor wire will connect to herm on the 55/5