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I have a Danby DPAC8399 air conditioner, and its fan motor started acting strangely. Sometimes, it it will only do a hum and won't start, and other times it will do that hum for a few seconds and then start in the wrong direction. I can help the motor by giving a push to the fan so it starts in the proper direction. From these symptoms, I though the start/run capacitor was bad. So I measured it with a multimeter and it displayed 7.72 μF, which is in range for an 8 μF ±5% capacitor. Still, I replaced it just in case, but the motor is still having the same behavior.

Now I am wondering what to check next. Is there a way to know whether I have to replace the PC board or the motor itself?

Here is a picture of the motor and its plate:

enter image description here

In case it can help diagnosing the problem, I measured the resistance between the different wires (Updated with values measured while motor disconnected prom PC board):

Color Yellow Blue Black Brown (Neutral)
Red 11.2 Ω 15.1 Ω 21 Ω
Yellow 5.1 Ω 31.5 Ω
Blue 46.5 Ω
Black

The fan has 3 speed (Low, Med, High) and I measured the voltage between the ground and these wires for all the speeds:

Speed Yellow Yellow Blue Black Brown (N)
High 123.5V 124.1V 124.5V 20.15V 0.5V
Med 105.8V 123.5V 127.0V 12.96V 0.425V
Low 94.2V 113.5V 123.5V 12.55V 0.4V

The air conditioner has 4 modes (Cool, Heat, Dry and Fan), but I did all my test in fan mode only.

Picture of the PC board:

enter image description here

Picture of the PC Board on which you can see the capacitor at the bottom:

enter image description here

On the right of this picture, you see the 5 colored wires going to the motor. Outside these wires there is a ground wire, and an orange and a white wire going to the capacitor:

enter image description here

The original capacitor and its specifications:

enter image description here

UPDATE:

I am also wondering why the black wire has infinite resistance with the other motor wires and has only 20 volts or less. And why the brown wire has only 0.5 volts or less? Does this look normal for such a motor?

UPDATE 2:

Well, it was quite a bit of work taking the motor out of the AC. It is definitely not meant to be serviceable unfortunately. And no luck finding a centrifugal switch. See the pictures of the open motor:

enter image description here

enter image description here

Also, I am wondering what the symbol means on the brown wire on the diagram:

enter image description here

UPDATE 3:

I ordered a new PC Board and swapped the PC Board, but that did not fix the issue. The motor still sometimes starts in the wrong direction.

UPDATE 4:

I managed to find a new motor and swapping the motor fixed the issue.

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  • \$\begingroup\$ Does anyone know what the black wire is for on the motor? It is labelled as "SL". I don't know what that means. \$\endgroup\$ Jun 16 '21 at 14:23
  • \$\begingroup\$ The SL might indicate 'shield'; perhaps it grounds the metal of the fan case etc. That's consistent with the ohms readings. \$\endgroup\$
    – Whit3rd
    Jun 17 '21 at 1:32
  • \$\begingroup\$ @Whit3rd There was in fact a green and yellow wire from the case to the ground that we cannot see on the pictures. Just to be sure, I tested continuity between the black wire and the case and there is none. I was wondering if it meant "slow" and if there is a slower speed than Low on this fan. It is not a speed that I can select in Fan mode though. I have also been wondering if that wire was supposed to help start the motor for a brief moment at start up. \$\endgroup\$ Jun 17 '21 at 11:48
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An AC motor which uses a start capacitor will exhibit this behavior if the capacitor is not connected; it is possible that this motor has a centrifugal switch, which should start the motor by connecting the capacitor until spinup is achieved; dirty contacts on such a switch will make it hard to start, and sometimes just hum. The centrifugal switch will be affixed to the rotor, inside the motor bell housing.

It is also possible that some other switching mechanism (maybe one of the relays?) is intended to be a starting switch, so it might be useful to trace the capacitor's wiring and see if it has a relay connected, which does not have electrical continuity from its COM to NC terminals (this can be checked with power disconnected using an ohmmeter).

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  • \$\begingroup\$ Unfortunately, I could not find a centrifugal switch nor a relay or any other component on the capacitor wiring. \$\endgroup\$ Jun 16 '21 at 3:13
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    \$\begingroup\$ This is a run capacitor and not a start capacitor, as you can see the wiring on the label, the capacitor is directly connected to the winding without any switch. \$\endgroup\$
    – Damien
    Jun 16 '21 at 4:19
  • \$\begingroup\$ @Damien Yes, you're right. The most likely phase to be missing, then, is not that one. Perhaps the relays to the other windings? Or, the connector joints on the printed circuit? \$\endgroup\$
    – Whit3rd
    Jun 16 '21 at 4:31
  • \$\begingroup\$ @Damien Does it mean that there is not start capacitor for this motor? There is another large capacitor, but I thought it was for the compressor motor. \$\endgroup\$ Jun 16 '21 at 4:38
  • \$\begingroup\$ If there are two big cap, it's possible the second one is a start capacitor, but given the motor size I doubt it would be needed, usually start capacitor are for fairly large motors that have high loads, not a fan. \$\endgroup\$
    – Damien
    Jun 16 '21 at 4:39
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A bad crimp on the connector of the orange or white wire could account for the failure to start because the capacitor would be disconnected. See if you can validate continuity between each connector and the conductor in its wire. Note that the orange wire is under stress and continuity may be intermittent depending on stress and position.

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  • \$\begingroup\$ One of the new photos shows that the current path to the capacitor goes through bayonet crimp connectors. That makes a total of six crimps to test and verify (male and female bayonets and the spade connectors, all x2). I can't tell you how many bad crimps causing sudden unexplained failures I've found over the years. \$\endgroup\$
    – MTA
    Jun 16 '21 at 12:51
  • \$\begingroup\$ I checked the crimps and I can see the wires being held tight in them. Unfortunately, I cannot test continuity in the capacitor wires (white and orange) as they go straight into the motor and there is not other end where I can measure from, unless I remove the insulation on the wire, but I did not want to do that. \$\endgroup\$ Jun 17 '21 at 0:26
  • \$\begingroup\$ @Jean-FrançoisBeauchamp A visual check suggests that the connections are OK but an electrical test would confirm it. The conductors can be broken where the crimped connector grips the insulation. \$\endgroup\$
    – MTA
    Jun 17 '21 at 1:33
  • \$\begingroup\$ I used a tool with a needle to puncture the wire and text continuity from the connection to the wire of both capacitor wires and continuity is fine, unless it is broken at the motor end. So I ordered a new PC Board for my AC and I'll see if that fixes the issue. \$\endgroup\$ Jun 29 '21 at 17:33
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A dead capacitor or a dead connection between the capacitor and the motor.

The capacitor-phase-shifted winding determines the motor direction. Without it, the motor can run either direction, provided you "show" it in which direction to start. If the motor is not "shown" where to go, it hums until either overheats or starts in random direction.

In some motors, the "starting" capacitor is disconnected by a centrifugal switch or a timer. Both the switch and the "start" winding may be defective as well, but the capacitor is the usual element to swear at and replace.

The underlying reason:

The easiest to understand motor is three-phase. The three windings powered by these 3 phases create a rotating magnetic field and the rotor follows it. In the single phase motor, the field doesn't really rotate, it just alternates between the two directions. It looks like rotating and the rotor can follow it pretty well, provided it already runs. And for starting in a particular direction, there is a separate winding wound at angle to the main one and powered by a phase-shifted voltage/current.

(There is a good example for a motor that starts in random direction by design in the microwave ovens. The table turns in whatever direction it feels like.)

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