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Starting capacitors in place on an air conditioning compressor (C) InspectAPedia.comQ&A on Electric motor starting capacitors
FAQs: Install of A/C Motor & Other Electric Motor Start-Boost Capacitors

  • POST a QUESTION or COMMENT about installing a hard-start capacitor to get an air conditioner motor, fan motor, or other electric motor running.

Electric motor starting or start-run capacitor FAQs.

This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment.

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Electric Motor Starting Capacitor FAQs

Photograph of This new compressor was placed directly against a brick wall. One third of its condenser coil cooling ability was blocked.These questions & answers about electric motor starting capacitors were posted originally at CAPACITORS for HARD STARTING MOTORS - be sure to review the advice given there.

The starting capacitor helps a motor start spinning by creating a high-torque, rotating, electrical field in the motor. In many electric motors there are actually two capacitors, one boosting the start winding (the start capacitor) and a second that remains in the circuit while the motor continues running (the run capacitor).

If the start capacitor has failed the symptom is that the motor won't start. You may hear the motor humming or observe that it's getting hot.

Watch out: If you observe a humming electric motor that is not starting we suggest that to avoid damage you turn off the system while waiting for repairs.

On 2019-11-16 by (mod) -

Do keep us posted, Jeff as what you find will certainly help other readers

On 2019-11-16 by Jeff


Thanks again Dan. That about lists all the possibilities. Since I already changed the capacitor I'll start looking at the wires themselves. Appreciate your help very much!
Jeff

On 2019-11-14 by (mod) - why does a motor run the wrong way or reverse its direction ?

ELECTRIC MOTOR RUN DIRECTION describes the usual causes,

Typically an electric motor running in reverse direction is caused by (in order of probabiliy)

A failed electric motor starting capacitor

A single speed single-phase motor leads are reversed on the motor's start widing connections

A single-speed 3-phase electric motor has two of its supply leads reversed

Belt driven air handler motors attached to a blower fan in a multiple-blower HVAC system can be turned backwards with the motor OFF and the squirrel cage fan rotating backwards because of air currents created by other fans that are on in the same system

(For 2-speed electric motors you'll need to contact your motor supplier)

Given that your motor seems to act randomly I would

1. try a new start capacitor

2. if that makes no difference I'd look for a loose wire connection or a winding that's loose or cracked and occasionally opening up in the motor itself.

3. or a bad centrifugal switch that's not switching the start cap in and out when it should. The switch ought to put the start cap IN when the motor is stopped and to take the start cap OUT when the motor gets up to speed. But if the switch is sticking it may not reliably connect the start cap.

Put another way, if the centrifugal switch is sticking you can get random choice of run direction when the motor starts-up again.

See ELECTRIC MOTOR CENTRIFUGAL SWITCH or PTC PRD

Well not in all motors. Some electric motors use a potential relay instead of a centrifugal switch. If the pot. relay is bad the effect of random start direction could still occur.

4. If a motor ALWAYS starts in the wrong direction we think the start winding leads have been reversed - that's not your issue

On 2019-11-14 by Jeff G

Hi Mod. I looked at your suggestions but can't quite find a situation where it runs in different directions each time (randomly). It's a single phase motor. Perhaps the "new" capacitor I tried was defective, so I may have to get another one and see if it makes a difference.

On 2019-11-11 by (mod) -

Jeff

Try the on Page search box to search for our article on

Electric motor runs backwards

Where you'll find a description of common causes and diagnosis and repair

On 2019-11-07 by Jeff G

My condenser unit fan runs in different directions each time it turns on (randomly). Sometimes it blows (correct direction) and sometimes it sucks (wrong direction). I've changed the capacitor because it used to just stall until I gave it a spin, but now it seems to randomly spin in whatever direction it wants.

On 2019-10-30 by (mod) - blower motor is a two-speed motor and the low-speed winding has apparently failed

Les

Thank you so much for following-up as what you report will help other readers. I'll be sure to keep the two-speed motor failure diagnosis in this article series - this was a failure that I'd not considered.

On 2019-10-30 by Les Kinman

Disregard...found my solution. It turns out my blower motor is a two-speed motor and the low-speed winding has apparently failed. The thermostat "ON" setting runs the fan at the A/C speed, and that's fine, but the heat speed is fried. As a temporary solution, I jumpered the two hots together so that it runs at the same speed whether on cool or heat. Works fine now.

...

After searching extensively, I decided to post my question to the community. When in heat mode, my forced air gas furnace will not kick on the blower motor when it reaches the set point on the fan control switch. I can hear the "click" but the motor doesn't start. However, if I turn the fan to "ON" on my thermostat, the blower motor comes on and runs fine. With voltage across the fan control switch terminals, why won't the blower come on with heat, while it will come on via the thermostat? Appreciate any help.

On 2019-08-03 by (mod) -

I wouldn't buy any repair part without having a service technician check for system. The problem could be a bad fan motor or bad capacitor or something else such as a fan relay or control.

On 2019-08-03 by Carolyn

I forgot part of the story! When I noticed the outdoor fan wasn't turning I checked the fuse box. The A/C fuse was flipped and I reset it. When I went back to the a/c the fan was turning but then stopped. I tried resetting the fuse again but it didn't want to stay. So what would be causing the fuse to flip and the fan not to turn?'

If the fan in my outdoor a/c unit is not turning, is it the capacitator? I noticed the air coming out of the registers was not cold. When I went to check things out I noticed the outdoor unit wasn't running even though the fan from the indoor unit was blowing. When I started looking for the possible problem I read about compressor/Condensors and Capacitators that all seemed to have something to do with turning the fan. How do I know what it is that I need?


On 2018-11-29 by kevinl108@yahoo.com

My Kenmore heap pump (model #TCH260AKA1 lcp air-conditioner) outdoor unit trips my circuit breaker when thermostat calls for heat. If I turn the thermostat to "OFF" and turn on the circuit breaker for heat pump, the heat pump outdoor unit fan would start to run. It seems running smoothly.

Once I turn the thermostat to "HEAT", the heat pump would try to start the motor with a few clunks but fail to start. At this time the circuit breaker has been tripped and no power going to the heat pump. I can still hear the humming sound next to the heat pump (assuming that it's the thermostat continuing to call for heat). When this happens, I'm still getting heat from the AUX heating and my room temperature will go up slowly.

I tried a new capacitor and the heat pump could not start so it's not the capacitor problem for sure.

Please help! Thanks!
Kevin

On 2018-11-20 by (mod) -

Mike

Are you sure the issue is the capacitor? The replacement you describe should have been fine.

I suspect the issue is that the motor is seizing or otherwise failed.

On 2018-11-20 by mike

the motor is smoking and too hot when i replace the capacitor 161-193mfd 110VAC 60Hz with 161-193uf 125VAC 50/60Hz +65C
IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-04-16 by (mod) - my starting cap just has 2 wires

Not all motors use start/run caps;

And if there's a single cap with just 2 wires yes that sound like a starter - else if it included run there'd be a 3rd terminal on the cap and there'd be 3 wires.

When a motor will run when given a starting spin that's a good tip-off that probably the starter cap is bad

On 2019-04-16 by Gary

I have a Rheem blower motor that just hums, won't start. motor & wiring are ok.. I can't find a start cap. only a run cap

I looked at wiring & only shows a run cap. with 2 brown wires tapped to motor. could this be my start cap. if so I tried a new one, still hums . will run if you spin motor.any ideas?

On 2019-02-27 by chris

Good morning. I have a Saer 1.1.kw pump that I use on my wellpoint. Last week the capacitor was replaced and from then on the pump runs for about an hour, switches of and restart automatically after +- 30 sec.

The longer the pump runs the shorter the intervals. It never did this before. I asked the person that replaced the capacitor why this is happening, he did not have an explanation.

What can I do to stop this because it is frustrating as each time the pump starts it sucks sand into my irrigation system, previously it was not a problem, but with the frequent start it is. Thank you

On 2018-11-29 by Aerovox

Id # 103414-07 Aerovox

P104F 310 370VAC 6U- 41-F_6o29

On 2018-10-29 by (mod) -

Take a look at the terminal markings on the capacitor, Barbie and the wire it just as we described above on this page.

On 2018-10-29 by Barbie

I have a new dual run capacitor for an outside central ac unit. It is the same as the one that came out of unit..in order to get the right one I unhooled the wires...Im wanting to make sure I get it right. I have a brown wirre that extends up to the fan area , another wire that goes to I am guessing gthe compressor it is a black tubular round part .

Then the other wore leads to some black box which is about two to three inches with other wires going into it..I have a fan a hermit and a c places to hook it up what goes where

On 2018-08-27 by (mod) -

We need to know what the original 2 pin capacitor was doing: starting cap or run cap,
We need to know what the new capacitor is providing; for example it may be a combined start+run capacitor.

You will select either the start or the run terminal depending on what the original capacitor was doing, and the 2nd wire will be the common wire.

On 2018-08-27 by Errol Anderson

How do I connect a four (4) pin capacitor to a table fan, which originally used a two (2) pin capacitor? Thank you.

On 2018-03-10 by (mod) -

re-posting

Kt kimball said:
Have not herd back robert .?

(phone weather report image deleted)

On 2018-03-10 by (mod) -

Typical capacitor wire color codes are given in the
HOW TO WIRE up a START CAPACITOR article https://inspectapedia.com/electric/Starting_Capacitor_Wiring.php

On 2018-03-10 by Kt kimball

Robert need color code for the 2 run cap on the magnetek

On 2018-03-10 by Kimball

Robert from info you asked for

On 2018-03-10 by Kt Magnetism part 177660_02. 230v 3450 rpm 22.0 amp type coast code g enclosure do serial bp8.052 made in USA

Magnetism part 177660_02. 230v 3450 rpm 22.0 amp type coast code g enclosure do serial bp8.052 made in USA photo 1 insulator class b1+ form KHH

I have a magnetek 5hp 230 3450rpm has 1 start cap and 2 run cap 1.has1blue 1white 1 brown the other 2blue and 1 brown 1 Orange rated at 25.0mfd 370 or 440 which wires go where thanks


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