Knowing how to test a pool pump capacitor can save you time and money when the pump motor fails. Every day that a pump is down, the likelihood of a lengthy and expensive cleanup increases. Troubleshooting a pump motor should begin with testing the capacitor(s).
What Is a Capacitor?
The basic definition of a capacitor is a device that’s used to store an electric charge. Most pool pump motors utilize a start capacitor and/or a run capacitor. They both look similar to a large battery. Start capacitors are usually located at the back of the motor and the run capacitor is located at the top of the motor.
Symptoms of a Bad Capacitor
Humming. Is your pool pump motor humming, but not turning on? Most pool motors require extra torque to get the motor up to speed. A failed capacitor will prevent the motor from turning over. Another cause of humming could be a seized motor shaft. If you can spin the motor shaft manually, the capacitor is likely the cause of the humming. If the shaft does not spin manually, the bearings or complete motor should be replaced.
Overheating. It is common for pool motors to run on the hot side. However, the motor will shut itself down if it is running too hot. A defective run capacitor can cause the motor to run at a higher amperage. Higher amps mean more wattage and more wattage means more heat. Other symptoms of a pool motor overheating would be an oversized impeller, bad windings or high voltage.
One Speed Working on a Two-speed Motor. There are a couple reasons why a two-speed pool pump motor would only run on high or low speed. As you can probably guess, the run capacitor is a frequent offender. If it’s not the capacitor, it’s likely a bad phase winding and the motor needs to be replaced.
Testing the Capacitor with a Multimeter
- Remove the cover at the back of the motor or on top of the motor to expose the capacitor.
- The capacitor will store an electrical charge. It will need to be shorted out by placing an insulated screwdriver across the leads of the capacitor. CAUTION: Capacitors have been known to explode when shorted out. For this reason, wear eye protection and place a cloth over the capacitor before shorting it out.
- Remove the leads to the pool pump capacitor. Note the placement of the leads so that you can restore them to their correct positions when you reconnect them.
- Set the multimeter on ohms to 1K.
- Slip a heavy piece of paper between the points on the switch.
- Attach one probe to each terminal. On an analog meter the needle should move rapidly to right then slowly drift to the left. If a digital meter is used, readings should start low and rapidly increase to maximum value. If the needle or number starts at zero and doesn’t move, the capacitor is bad and therefore needs to be replaced.
Replacement
Replacement capacitors must have the same MFD or UF rating as the original. If the same voltage rating is not available, it is acceptable to use the next higher voltage. For example, if a 370 volt unit is not available, use the next rating which is a 440 volt.
Other Related Content
How to Replace a Pool Pump Capacitor
Hi Matthew,
I am not sure how to attach a picture but the info on the label is as follows:
Pump Model No. / Part No. is SF-N1-3/4A /340037. Manufacturer is Pentair SuperFlo. 3/4 hp with 0.94 S.F.
The capacitor on the top is
Genteq 97F9606.
25 uf
+6 -6 %
P10000AFC
628318-307
I’m not sure if that is the starting capacitor or if that is the running one and the starter is elsewhere. I get a humming when the power is switched on. I can manually turn the impeller so it isn’t stuck or seized.
Thanks for any info/advise you can offer.
This would be the replacement capacitor AO Smith Replacement Run Capacitor, 25MFD 370V
As for the actual troubleshooting of the capacitor or testing it, follow the steps in the article.
What’s the part number for the start capacitor for the SF-N1-3/4A (340037) ?
What is the part, model, or catalog number on your motor’s label? A picture of the motor label would be most helpful.
Hi
My pump humms for a few seconds then trips the breaker the pump spins freely
Could it be the capacitors
It could be. You should test it.
Hi, My hot tub pump will not always start on slow speed. It just hums…. but if I press the button and put it on High speed, it will start… then I can reduce it on slow speed and it works… What’s confusing is that most of the time it will start on slow speed… seem like it will not start everytime and humm… is that a capacitor going bad? or do capacitors goes bad all the way? Thanks!
It could be the capacitor as there is a hum. Have you tested the capacitor?
Hi
I have a Jet 102m that is working when connected to power but has little or no pressure.
What do you suggest i do?
Woke up this morning and pool pump was not running. I have power to both the timing box and pump itself. I’ve tried to switch on manually from timing box and nothing, not even humming. Also I can turn the motor shaft freely by hand. Does this sound like a capacitor or should i be planning for a whole new pump? Current pump is a Pentair 1.0 model number/part number SF – N1 – 1A / 340038
Since you are already testing the wire voltage, you may as well test the capacitor just to clear it from the list of possibilities. If the capacitor or the motor is the only issue, the housing is still in good working order, then all you need to do is replace the failed part.
Hi! About a year ago my Polaris booster pump stopped working. All it would do was make a horribly loud humming/buzzing noise – and I’m just getting around to it (I know, I know). I watched one of your videos about capacitors yesterday which inspired me to think that I might be able to fix it on my own. I looked last night and found the following information:
PB4 Booster Pump – Enclosure Type 3
Century Pool & Spa Motor 1081 Pool Pump Duty
Serial 056103M
Part 7-173840-23
HP 3/4 SF 1.5
HZ 60 RPM 3450
Volts 230/115
My question is this – I didn’t take the capacitor cover off last night because it was almost dark. Do I have to take this off to get the information that I need to order the correct capacitor to try or is the information that I gave above enough to know which to order? Also, I haven’t tried to turn the pump on in at least 6 months since it stopped working. The hum is not as loud now as it was then. Does this mean that now there’s something else wrong?
Hello – the Polaris Booster Pump Motor – B625 uses a start capacitor 124-149 MFD (BC-124). The hum is a sign the capacitor is failing.
How long should a capacitor last, mine are only lasting a few months?
I don’t know the exact expected lifespan of a capacitor, but it is definitely longer than a few months. if you are replacing them that often, you have something causing them to fail. We list the common causes and how to fix them in this guide: PSC Ep. 86: Why is my pool pump motor capacitor failing?
I have a Sta-Rite Dyna-Pro-E Pump (2-Speed) #MPEA6YG-207L that will only run on low speed. It will sometimes run at high speed if I flip from low to high while it is already running but then it shuts down a short time later (overheating?). It will not start on high speed. The motor is #AE100GLL-Y. What capacitors would this take?
This guide gives you a few other things to check: My Pool Pump Runs On Low Speed But Not On High Speed. The AE100GLL-Y uses a start capacitor 2509516-002 and a run capacitor (628318-309)
YOU GUYS ARE KILLIN ME ! SO MUCH BAD ADVICE HERE! I’M A TECH AND THERE ARE GAPS IN MANY OF THESE COMMENTS . ALL OF YPU SHPULD BE CALLING A MOTOR TECHNICIAN. NOT AN ELECTRICIAN OR POOL GUY BUT A TECH. ONLY FOUND USUALLYIN HVAC OR MOTOR REPAIR INDUSTRY.
Spoken like a true unbiased professional.
Hello. I have a Hayward pump sp32152ee. Which start and run capacitors do I need? 1.5 hp dual speed. Thx
The run capacitor is the 628318-307 and the start capacitor is PTMJ189
pump was shut off this morning tripped circuit breaker Pump model Pentair 1.0 HP whisperflo WFE4
ran for a second then tripped again
Now once you reset it it trips immediate
checked pump motor shaft spins fine not frozen
Think it is the capacitor ?
Rob take a look at the dropbox URL – I posted a pic of the capacitor. Do you sell this?
The pump is the 3/4 HP (using it for solar)
Specs ono cap: 15uf 370V
The picture you posted is the run capacitor. The run capacitor is part number 5270-01. There should also be a start capacitor at the back of the motor. You’d have to remove the end cap to see the start capacitor.
Ahhh I didnt realize there are two caps. I’ll look at the start cap. Thanks for your attention.
Thanks for the quick reply! I’ll take a look at the Cap but I believe the motor is 230v. From reading it sure seems like the capacitor is a common issue on pool pumps 🙂
Video and pics of pump https://www.dropbox.com/sh/mwrt559rjr6bx77/AAAIVfUqITO6I82HeKojQjEya?dl=0
The capacitor voltage can be different from the motor voltage. It doesn’t always match. You can have a low voltage capacitor and a high voltage motor.
Hello my Pentair Sta-Rite P6E6D-205L doesn’t start. When turned on it hums for 7-8 seconds, then a single relay click sound comes from the motor and it stops humming. If I leave it alone in the on position it repeats this every 5-10 minutes. What do you think I’m dealing with?
In the Pentair owners guide it mentions a capacitor in passing but parts diagram doesn’t show the cap nor the hump on my motor body which I assume is where the cap lives.
Hello Rob – It sounds like a bad start capacitor. The start capacitor is usually located at the back of the motor. The replacement start capacitor for the P6E6D-205L should be part number 5270-11. The MFD/UF rating is 124-149 and the voltage is 110-125. You can verify the specifications by looking at the start capacitor on your motor.
My pump runs for 5-10 seconds and shuts off. Will come back on maybe about 3-5 minutes later and repeat the same thing. I recently replaced the seals on the shaft and impeller but made no other changes. I’ve triple checked the orientation and placement of the seals, etc. I have ~123 volts while it is on and does not drop or spike voltage. I had no problem prior to replacing the seals. Also, the circuit breaker in my box is NOT tripping. What gives? Thanks for any help.
Have you tried testing the capacitor?
My pump started making a loud sound then it just cut off. Been running good now nothing… Any suggestions?
If the motor shaft spins freely, it could be a bad capacitor. You can test the capacitor by following the steps in the article above.
Hello there,
Motor shaft spins freely.
I replaced the capacitor and still humming and won’t fire up.
?
Check the winding resistance and the voltage of the lines feeding the motor.
From that small description of the problem, no I can’t diagnose it. But have you tried completing any of the troubleshooting mentioned in our guides? How To Determine Why a Motor Won’t Start or Shuts Off
Hello,
back in Dec i purchased a Run capacitor from here. It failed again last weekend. I purchased a new one from you guys and it’s working fine. But what would make the run capacitor fail so quickly?
I asked a question back in December regarding if the run capacitor i was looking at was the correct one and you guys said yes.
Thanks in advance
Run capacitors can fail for several reasons.
1) Wrong capacitor. This could happen if the wrong MFD value was used, or a 370 volt was used where it should have been a 440 volt.
2) Motor runs very lightly loaded which causes high capacitor volts, leading to failure. Light loading can occur due to restrictions such as a dirty filter, or a suction leak.
3) Capacitor may have had a defect from new.
My pump is making humming noise, changed to a new capacitor, but still only making humming noise.
The can turn the impeller freely from the back.
What else can I try?
It sounds like a bad phase winding. Sometimes they will run continually once they are helped along. Other times, they will be weakened enough that eventually, they will trip the motor overload. At this point, we would recommend replacing the motor.
Hello i have a water pump i nesd to know with which capacitor will work (my pump it has HP 1.3)
We’d be glad to assist you. What is the catalog or part number of your pump motor? This will help us determine the capacitor.
Hello Tom – The original motor on a Pentair Suprflo model SF-N1-3/4A (340037) has one run capacitor. It does not have a start capacitor.
I have a Pentair 2.0 HP motor model number 184214- does it have 2 capacitors? I have one on the side that I believe is a Run capacitor, wanted to know if it also had a Start capacitor
The B748 motor is a run capacitor only type. The replacement capacitor is 2444
Hi my name is yomi my pump is not humming and all the cables are well connected
Motor not humming ! Circuit breakers are good and there is power to motor ! Does it matter If capacitors are bad if there is no “humming” from motor ?! Motor has power but seems to be DEAD !
The motor may be dead if you have power properly applied and you hear no noise. Make sure that the wiring at the motor terminals is in place. The wires can loosen up over time and there may not be a good contact between the wires and terminals. You can test the capacitor, following the directions above, in order to rule it out as well.
I have a Jandy Stealth 2 speed pump. Capacitor blew out today (had replaced it 2 years ago). The old capacitor
was by Genteq 50/60Hz 370VAC. The new one I bought is a 25 MFD 440V run capacitor. What is the difference between the two? The good news is, since I am familiar with having done this before (pool built in 2009), it was very easy to replace and pool started right up!
Hello Mary – The obvious difference would be that the new capacitor has a higher voltage. That’s fine as long as the MFD rating was the same (25) on the old capacitor.
‘5. Slip a heavy piece of paper between the points on the switch.’ umm what does that mean?
Hello Bob – The paper is used to isolate the circuit. The best way is to short the capacitor with an insulated tool and then remove one of the wires, which will also ensure that only the capacitor is in the circuit being tested.
I think this is a preventative measure to make sure that your testing leads don’t touch and cause an arc across the two contacts of the capacitor