How To Replace a Pool Pump Capacitor

Written by:  Danny Rhodehamel

Save yourself the cost of a new motor. Check the capacitor first. When you turn on your pump and the motor produces a humming sound, the motor may be frozen so that it won't turn or you may have a bad capacitor. Check the capacitor. It can be replaced for a fraction of the price of a new motor. Note: Some motors have two capacitors: a run capacitor and a start capacitor. If so, check both.

Tips & Warnings


Things You'll Need

Step by Step

Step 1
power pool pump

Turn off the power to the pool pump. For maximum safety turn the power off at the circuit breaker.

Step 2
pool pump capacitor hump cover

Depending on the make of the pool pump, the capacitor will be under a hump cover on top of the motor, or it will be under a cover on the electrical end of the motor, or both. Some pumps have both a run capacitor and a start capacitor. The run capacitor will generally be rated at 15-50 MFD and 370 VAC. The start capacitor will generatlly be rated at 50-400 MFD and 125 or 250 VAC. This picture shows the location of the capacitor under a hump cover.

Step 3
pool pump capacitor

This picture shows the location of the pool pump capacitor at the end. In either case the covers are normally held on with two screws. Remove these screws to take off the cover and expose the capacitor. This capacitor is about the size of a roll of half dollars.

Step 4
pool pump capacitors

Pool Pump Capacitors store an electrical charge that can shock you even when the power is off. Before removing the capacitor, discharge this energy by placing a screwdriver across the leads of the capacitor. CAUTION: Capacitors have been know to explode when shorted out. For your protection wear eye protection and place a cloth over the capacitor before shorting it out.

Step 5
pool pump capacitor

If the capacitor is located at the end of the pool pump, remove the single screw that secures a clip holding the capacitor. Note how the plastic strip is positioned between the clip and the capacitor. It will have to be replaced in this position to keep the capacitor from shorting out on the motor. If the pool pump capacitor is on top of the motor, it should be free after you have removed the cover and the capacitor's leads.

Step 6
capacitor leads

Remove the leads to the pool pump capacitor. Note the placement of the leads so that you can restore them to their correct position when you reconnect them.

Step 7
rating on capacitor

Check the rating on the pool pump capacitor for replacement specifications. They will vary by manufacturer. Look for their MFD (or uf) and VAC specifications. For example, this one is a start capacitor rated at 124-149 MFD and 125 VAC. Try to replace the bad capacitor with an identical capacitor. If the exact capacitor is not available, you can use one with slightly higher capacitance. Do not use one with a lower rating.

Step 8

Use a multimeter to verify that the capacitor is bad. Using the lowest ohms setting, touch the meter leads to the pool pump capacitor's terminals. If meter remains at 0, you know that the capacitor is bad. Check the new capacitor to verify it is good. First short out the terminals on the new capacitor to reset it. Then touch the meter leads to the capacitor terminals. If the capacitor is good, the meter will jump up to the other end than slower back off to 0.

Step 9
pool pump capacitor

Connect the motor leads to the pool pump capacitor and secure the capacitor in place as required. Watch the placement of the plastic strip as mentioned above.

Step 10

Replace the cover.

Step 11

Reestablish power at the circuit breaker.

Comments (1 to 40 of 64)

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User: Inyopools

gmark – I don’t think it is the capacitor. A start capacitor is only operational on start up until the motor reaches near full rotation, and then it cuts out. So it wouldn't be cyclic unless the motor is slowing down periodically for some other reason. I would take the motor out of its housing and see if there is debris around the impeller or if the impeller is loose and rubbing against the diffuser. It may also be your motor bearings starting to fail.

User: gmark

Need help, I was hosing off my pump pad and my flo tech pump started making a loud humming sound and smelled like it was melting. This lasted 30 second s or so then started working again. It continues to cycle this wayour constantly every few minutes. Could the capacitor work intermittently

User: Inyopools

Pete – The majority of pumps use an A.O.Smith motor like the one shown in this guide. If your pump uses an A.O.Smith motor (see motor label), wire the capacitor as shown in step #6. If not, I would recommend calling the pump manufacturer.

User: Pete

Hi, I'm replacing my capacitor and don't know which terminals to hook the wires on because it's a different brand. How do I know which one to hook up. Can I damage the pump if I do the wrong one?

User: Inyopools

klst21655 - Sounds like either a bad capacitor or a short in the motor windings. If windings, you will have to replace the motor.

User: klst21655

My Hayward Super Pump makes a very loud buzzing noise when turned on. The Impeller turns freely but Pump will not run. Capacitator?

User: Inyopools

csitg - The "POP" would indicate something electrical. Take off the back cover of the motor and check the motor's capacitor (if it has one) and its thermal protector. See our guide on "How the Common Capacitor Start Pool Motor Works" to see where these parts might be.

User: Inyopools

Motor stopped - See these guides: "How To Determine Why a Motor Won't Start or Shuts Off" and "How To Troubleshoot a Pool Pump Motor - Motor Fails to Start".

User: csitg

I have a Flotec pump, I really don't know how old it is but while walking by it yesterday I heard a "POP" then the pump stopped working. Any suggestions? Thank you.


I have a 1hp Hayward Super Pump. All summer it's been working beautifully. Yesterday it stopped working. We had alot of rain,so I'm guessing that bhad something to do with it. In 20+ years it never happened before. I checked all the breakers etc. I was hoping to find a re-set button. Had no success. Any Ideas?

User: Inyopools

Raj - The winding in your low speed circuit may be bad. You may have to replace the motor. Check first that your wire connections to the pump terminal are tight.

User: Raj

I have an AO smith K48L2A1 motor in my spa.

The pump will not start at low speed, it simply hums and then stops. The pump will start at high speed and will run at low speed once it has been started (no load).

I had both the start and run capacitor tested, and they passed. But to be sure, I replaced the start capacitor anyway (original 124-149) (replacement 130-156MFD). But this still hasn't resolved anything, and the pump will hum and not start at the low speed.

Any ideas what to try next?

User: Inyopools

scott44 - This sounds like a voltage issue. Starting then shutting down after a few seconds is characteristic of having 115V supply voltage going into a pump that is configured for 220V. Also check that the wiring to your motor is not damaged and that you have tight connections to the motor terminal.

User: scott44

My AO Smith 1 1/2 hp 3600 rpm motor starts, but makes an odd noise and is clearly not going 3600 rpm, more like 500 rpm. Then shuts off after a few seconds of this. Could this be a capacitor problem?

User: Jpstone13

So installed a matching capacitor in mfd and hz yesterday although it was a different brand. I know it is important to hook it up properly but when I took the new one out it had side posts as opposed to vertical when in a similar position. I installed it and turned the pump on and tho it did start, if made a high pitched noise and then a pop followed by a spark that tripped the circuit and shut off. Two questions. One, did this happen because I hooked it up incorrectly or could it be that the motor was already bad? Two, did I just ruin my motor by doing this?

User: Inyopools

JamesTheTruth - The start capacitor is generally in the back of the motor under the cover. I would assume that you replaced that capacitor already. Some motors also have a run capacitor on top of the motor under the hump. Your motor does not have a hump, so only one capacitor. If your motor is still humming, I would guess it's has a damaged windings coil and will need to be replaced.

User: JamesTheTruth

I have successfully replaced the capacitor but pump but pump still Humes then freezes. Dealer said there probably is a starter capacitor also which needs replacing. Where is the starter capacitor located on a A.O. Smith UST 1102 1HP 3450.

User: Inyopools

txtngauge - Assuming you protected the motor from freezing (if applicable), it should work now. Use a multimeter and check the electrical circuit to your pump to make sure you are getting power to the pump. Check the wiring under the motor cover to make sure the contacts are tight.

User: txtngauge

Just tried to start up our pump and NOTHING...the pool is only 3 years old and we had no problem before closing the pool last fall. any suggestions or is it just time for a new motor?

User: Inyopools

Gampopa - If the low speed failed in the pump, you would probably have failed low speed windings and they would create smoke. Your problem is probably due to a failed pneumatic switch.

User: Gampopa

We have a Waterway 4 hp 56 frame 2 speed pump for our hot tub that seems to only work on high speed. When we hit the pneumatic switch to go to low speed there's no sound nor flow nor vibration from the pump. Could this be a capacitor problem or something else? I want to avoid pulling the pump and heater control out again to have it serviced.

User: Inyopools

help - Some motors for spa and jetted tubs and above ground pool applications do not use capacitors. See our guide on "How To Identify Pool Motor Types" for more information.

User: help

I have a AO smith flex 48 1.5 HP

I cant find the capasitor

User: Inyopools

motor wire sparked - Components in the motor may have been shorted when the wire sparked. See our guide on "testing the motor windings resistance". If that doesn't help, take the motor to a local motor shop and have them do a more complete check.


I have a Utilitech 1HP motor 230V. On the back of the shaft is a device with springs hooked to it. This device nicked one of the hot wires coming into the motor. It sparked and I turned it off and now it will not start. I fixed the problem and I have power to each wire to the motor. The motor will not start. Help

User: Inyopools

Mark - As a final comment on our previous communications, the engineers at the manufacturers suggest upping the voltage on your 35 MFD,370 V capacitor to 440V. The voltage represents the voltage the capacitor can handle, so the 440 would be more resilient.

User: Mark

I have a Hayward Northstar Pump with a 2.0 HP USN1202 moter (AO Smith). Over the last 4 months, the motor has started failing. A friend suggested changing out the capacitor. I did this and the system starts working again. Then in about 1 month, the motor fails again. Replaced the capacitor, works fine...for about a month, then fails. Any idea on what could cause the repeated failures of the capacitor? Should I replace the motor or could the problem be elsewhere?

User: InyoPools

Jim - I checked your question on capacitors with a motor expert at the motor manufacturers, and he stated that the capacitor replacement would not degrade the pumping capacity of the pump.

User: Jim

Could a capacitor be a cause of a weak pump? I've replaced the capacitor on my pump because it went bad but now my pump can't suck in enough water. It doesn't pull enough to use the vacuum path or the skimmer path by themselves, so when together, there's not enough suction to vacuum the pool. The small basket by the pump looks like it's pulling in air but I've checked all the seals, replaced every single gasket, used the proper "sealant" on them, etc. Could the capacitor be the problem here or is it the pool motor?

FYI, the problem and the capacitor replacement dates do not coincide, just making note of a change.

User: InyoPools

weekend engineer - No. The startup capacitor will change up almost immediately.

User: weekend engineer

does a new start capacitor or a discharged start capacitor (due to removal to work on the motor), have to have a charge period before the motor will start?

User: InyoPools

rich man - According to the motor rep - Three phase motors cannot be used on single phase power as far as we are concerned, from a warranty standpoint. They require a drive that converts single phase to 3 phase.

User: txt

how do i check if my motor is ok using a mutimeter

User: rich man

please explain to me how to connect a 3phase motor to single phase supply coz it is an old motor with no markings on the wires.
Also tell me how to connect the start capacitor

User: InyoPools

spanishmoss - Yes the ohms test is performed with the capacitor disconnected.


thanks for your clear and informative step by step guys rock......R. S. Miller Tucson,AZ.

User: Rick

I just wanted to thank you all for this very helpful and informative site.You rock thanks.....Rick

User: spanishmoss

Good article. I'm replacing a 30mfd 370vac/b capacitor which has two terminals. Are the terminals interchangeable, or is one positive and the other negative? Also, will the ohms test work if the capacitor is not hooked up to the motor? Thanks

User: InyoPools

Ed - If your motor shaft does not turn freely, your motor bearings are probably going. When the motor gets to this point, most people buy a new motor.

User: Ed

Seems the motor is a little difficult to turn. Pulled the motor/impeller from the housing, and tried to turn the impeller. Not too easy. Motor does not start, hums for a few seconds, then trips the breaker. Ideas?

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Tips & Warnings

The run capacitor will generally be rated at 15-50 MFD and 370 VAC. The start capacitor will generatlly be rated at 50-400 MFD and 125 or 250 VAC.

Discharge the pool pump capacitor before removing it to avoid a shock.

Disconnect power to the pool pump motor at the circuit breaker before working on the motor.

Please Note:

Inyo Pool Products is not responsible for any injury or damaged equipment
while using our guides. Using our guides is doing so at your own risk.
These guides are suggested use of your pool or spa equipment and may vary
depending on which product you are using.