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Thread: A/C fan motor capacitor wiring

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    Coco is offline New Member
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    A/C fan motor capacitor wiring

    My outdoor a/c unit fan motor was making lots of noise, so I replaced the motor. The old motor was an Emerson KA55HXGSY with 3 wires - Black, Purple, and Brown. The brown wire connected to the "fan" terminal of a dual capacitor. A hard-start capacitor was also wired across the "c" and "herm" terminals of the dual capacitor. The replacement motor is an AO Smith FSE1026SV1 with 4 wires - Black, Yellow, Brown, and Brown/White stripe. The new motor wiring diagram shows the Brown and Brown/White stripe wires going to a separate fan motor capacitor. I didn't get a new capacitor with the motor since the unit ran fine (just noisy fan motor bearings). I connected the Brown wire from the fan motor to the "fan" terminal of the dual capacitor and taped off the brown/white stripe. When I swiched on the a/c again, the fan started once and the a/c worked great for a couple of hours. It wouldn't start again after shutting it down. Just a clicking noise. I bought a new dual capacitor (35/5 MFD) and a new hard-start capacitor and installed them. Now I get a clicking noise and a faint humming. The capacitor specs on the old and new fan motor are the same (5MFD).

    Did I wire this new 4-wire motor correctly? Can you use a 4-wire motor with a dual capacitor? Where should the brown/white wire go to?

    Thank for your help.

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    LazyPup's Avatar
    LazyPup is offline Deity
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    In most AC condensing units both the compressor and the fan motor are capacitor run motors.

    Capacitor run motors have two separate sets of windings, the "Run Winding" and the "start Winding".

    The run winding is then connected directly to line 1 of the contactor. A second wire is connected from Line 1 of the contactor to one side of a capacitor. A second wire is connected from the second terminal on the capacitor to the Start winding of the motor. This configuration is putting the capacitor in series with the start winding.

    We must remember that this is an Alternating Current circuit which means the voltage rises from zero to peak positive and back to zero, then to peak negative voltage and back to zero 60 times per second. As the voltage is rising the run winding is energized and the capacitor is charging. The moment the voltage changes polarity the run winding is not energized but the current stored in the capacitor instantly discharges into the start winding. The two windings are placed in the motor at approximately 90 deg out of phase in rotation so that when one winding is not energized to otehr one is, thus it produces a more balanced output.

    If a capacitor run motor is run for even a short time without a capacitor the entire load is placed on the run winding which usually results in reduced RPM & motor overheating and failing.

    Typically an OEM (original equipment manufacturer) fan motor will only have three wires, Common (White) Run(Black) & Capacitor(Brown) which is actually connected to the start winding.

    When replacing an OEM motor with a universal replacement type we commonly find additional wires on the motor.

    Not all AC condensers use the same RPM for the fan, and not all fans rotate the same direction so the universal replacement motors allow us to configure it to the needs of the unit.

    The standard color code for a universal multispeed reversible motor is:

    White = Common
    Black =High Speed
    Blue = Medium Speed
    Red = Low Speed
    Brown = Capacitor

    Occassionally we find a second capacitor wire:
    Brown with white Stripe = Capacitor common

    Purple & Yellow for changing rotation.

    In your case your replacement motor is a single speed motor so it does not have the blue or red wires. The black wire is the run winding.

    For your motor the Black wire should be connected to line 1 of the contactor.
    The white wire is connected to line 2 of the contactor.

    If you were replacing with a multi speed motor you would chech the RPM of the original motor and select the color that corresponds to that speed on the replacement motor and connect that wire to line 1 of the contactor, then cut or tape off the two remaining wires.

    When the AC has a dual capacitor the center terminal of the capacitor is the capacitor common and is connected to Line 1 of the contactor.

    If you had a separate capacitor for the fan motor you would check the top of the capacitor for a red dot or an embossed dot near one of the capacitor terminals. That is the identified terminal and the Brown wire is connected to the identified terminal, then the brown with white stripe is connected to the opposit terminal on the capacitor. (If the capacitor has no identified terminal you then just connect one wire to each terminal.)

    The Brown wire from the fan motor is then connected to the capacitor "Fan" terminal and the Brown with white stripe is connected to the center capacitor common terminal.

    The HERM terminal is for the start winding of the "Hermetic Compressor"

    Some universal motors also have two purple wires and two yellow wires which are connected pruple to purple and yellow to yellow. That is for clockwise rotation. If you need counter clockwise rotation you then disconnect the wires an connect one yellow to one purple, then the other yellow to the other purple to reverse rotation.

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    Coco is offline New Member
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    Smile A/C fan motor capacitor wiring

    Thank you very much for your detailed response LazyPup! I read your posts on capacitors earlier, but my understanding of electricity and motors wasn't enough to figure this one out. I will hook up the brown/white stripe wire from the fan motor to the common terminal of the dual capacitor and give it a try. Thank you again. I'll let you know the outcome.

    Coco

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    Coco is offline New Member
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    Question A/C fan motor capacitor wiring - update

    I connected the brown/white stripe wire from the fan motor to the Common terminal of the dual capacitor. I still get a single click when the a/c is turned on, followed by a humming noise, but no condenser fan! The fan portion of the dual capacitor is 5MFD. Do you think I need a separate 5MFD fan capacitor? Any other ideas?

    The a/c unit worked fine except for the motor bearing noise. After I changed the motor it did a 2 hour cooling cycle with no problems. Ever since then, all I get is a click, and hum.

    Thanks for your help, Coco.

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    HayZee518's Avatar
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    Ain't sure but that "click" may be the thermal overload tripping.

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    Coco is offline New Member
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    HayZee, how long before you get a thermal overload? This click happens as soon as the thermostat is turned from "off" to "cool", and then the light humming starts. The fan motor never turns. I only have the power on for three seconds or so. Could it be a relay of some sort?

    More info. I tried hooking up the brown/white stripe and brown wires to the Common and Fan terminals of a second capacitor with the same result - just a click and hum.

    The new fan motor is shown as a replacement for the old on a cross reference chart. It is the same volt, hp, size, and rpm. The AMP rating of the old motor is 1.3. The new motor says AMPS 1.3, MAX LOAD AMPS 1.8. Is the new motor drawing more power than the old one, and possibly overloading another component?

    I was able to remove and reuse the original fan blade.

    Thank you very much for your help. I feel like I'm so close to getting this fixed, I'd like to be able to finish the job.

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    Coco is offline New Member
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    Update #2

    I did some further testing after suspecting a problem with the contactor. I read up on the operation of the contactor from a post from LazyPup (url below). Thanks!

    Troubleshooting Central Air

    I turned on switch on the thermostat from "off" to "cool". Got the same old click. Then I pushed in the plastic tab on the contactor armature with an insulated screwdriver and the fan motor and compressor started. When I released the tab, everything stopped.

    I located what I think are the #18 awg wires that should supply 24VAC to the contactor (they are on the L2/T2 side of the contactor, on the side). There is also a larger gauge black wire connected to one of the side terminals. Do I measure the voltage on the signal wires with the terminals connected, or disconnected? Should there be any voltage at the signal terminals with the signal wires disconnected?

    Do I check the voltage on each wire to ground, or just between the two signal wires?

    Thanks again.

  8. #8
    LazyPup's Avatar
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    All 24volt control voltage originates at your 24volt step down transformer which is usually located inside the indoor HVAC unit or wall mounted close to it.

    The power goes to the thermostat then to the AC condensing unit contactor.

    The contactor has an internal 24v electromagnet. When the thermostat calls for AC the 24v energizes the magnet and pulls the contactor armature down to complete the 240 volt circuit to the unit.

    To test the control voltage first turn the thermostat to AC and set the calling temp well below the room temp to insure the thermostat will be calling for AC.

    Locate the signal voltage connections on the contactor. They will be on the sides and will have the small diameter thermostat wires connected to them.

    Using a volt meter measure the voltage from one of those low voltage signal connections to the other. Do not measure from signal voltage to the heavy line voltage connects as this could damage your meter, the control components or your thermostat.

    While the control voltage is often stated as 24v it is not uncommon to get readings ranging from 18 to 24V.

    In your post you stated that when the thermostat is turned on you could hear a click but you got no responce until you actually pressed down on the armature with a screwdriver. Generally the clicking sound would be indicating that the magnet is energized and trying to pull the armature down, but for reasons unknown the armature is not moving far enough to effectively complete the circuit. This is very typical of a defective contactor. The armature may be fouled by dirt and debris in the slide mechanism or their may be a burned contact that is not closing properly. The best solution is to replace the contactor.

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    Coco is offline New Member
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    Thumbs up A/C working now

    The A/C is working fine now. I replaced the old single pole contactor with a new dual pole contactor. I'm sure the old contactor was in need of replacing, but when I changed the contactor, it didn't change the "symptom" I was chasing (see below).

    After replacing each part (motor, capacitor, and contactor) on the 17 year old York heat pump, I turned on the thermostat from "off" to "cool" and waited for the results. I didn't wait more than about 5 seconds to turn it off again if the fan motor didn't come on, because I was afraid of burning something up if I wired it wrong. Every time I got a click immediately (sounds like an electrical relay), but I have no idea what this noise is. Yesterday, I set the thermostat set temperature higher than the room temperature. Still got a click when I moved the switch from "off" to "cool". I then lowered to set temperature to 10 degrees below room temperature. I then had to wait for about 1 minute (60 seconds) before the compressor and fan motor came on with a much louder click from the contactor. If I hadn't tried it for a full minute, I'd still be looking for the problem with the unit. I have a programmable thermostat, maybe this is the explanation. Thought I'd pass on my experience for any other novice in the same situation.

    Thanks for helping me through this one LazyPup. I really appreciate your advice.

    Coco

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    Cmudr1 is offline Handyman
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    Quote Originally Posted by Coco
    The A/C is working fine now. I replaced the old single pole contactor with a new dual pole contactor. I'm sure the old contactor was in need of replacing, but when I changed the contactor, it didn't change the "symptom" I was chasing (see below).
    Congrats on getting everything working! Im still a little hazy though. You say it works after a min, then what is the first click sound you're hearing? Is it maybe the relay like you said getting power and ready to turn on with the thermostat? Is it that a normal sound you readily hear? Is all you had to do before was wait a min to come on, or is that just after replacing the contactor. Now I'm not an expert and dont mean to pry, but this thread happened to intrique me a bit. Im sorry im not able to offer any real advice, but after ready enough of fthese I might start to figure things out. Again good job on getting it working!
    Chris

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