Compressor continuity?

[Davej]

Opened up a dehumidifier and seem to have a shorted compressor? There
are three connector pins on the top of the compressor and I'm guessing
that NONE of them should show any continuity to the case, right?

Thanks.

[The Daring Dufas]

If any of the pins show continuity to the can, the coils are shorted and
compressor is bad. ^_^

TDD

[Stormin Mormon]

Yes? That is agreeable? NONE of the three
pins under the cover? Should have continuity
to the case?

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.
"Davej" <gal...@hotmail.com> wrote in message news:8a0e88ea-70c3-4736...@m4g2000yqe.googlegroups.com...

[Stormin Mormon]

How about if all three short to can?

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.

"The Daring Dufas" <the-dari...@stinky-finger.net> wrote in message news:kptimg$ql1$1...@dont-email.me...

[hrho...@sbcglobal.net]

Isn't it likely that there are one hot lead and one neutral lead, and
one safety/ground????? Assuming that it is a 120V circuit!!!

[gregz]

Any experts here ? I don't see many good answers.

Greg

[Fat-Dumb and Happy]

One of several on youtube, this is for a 220V system
http://www.youtube.com/watch?v=4RfepFb1Dx8

[The Daring Dufas]

The three pins on most single phase compressors are "C" Common, "S"
Start and "R" Run. The power is hooked to C and R. The capacitor or
start relay is hooked to S with the other side of the capacitor
connected to R. The neutral is hooked to C common and line to R run.
If it's a 120vac compressor there may be a start relay connected so
you should follow the wiring diagram. Some units may have two capacitors
that are connected to the R run terminal through a start relay with a
start capacitor and a run capacitor. There is usually a
wiring diagram on a panel cover or on the insulated cover for the
terminals on the compressor. ^_^

TDD

[nestork]

No, what those three pins are are connections to the start winding, the
run winding and the common.

Take a look at this representation of a typical induction motor:

[image:
http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee11/IMAGES/MOTORS_FIG6.GIF]

That thing you're looking at is called a "stator". A magnet, or a rotor
with windings on it that turn the rotor into an electromagnet rotates
inside the stator.

Note that the same wire wraps around both vertical poles, and a second
wire wraps around the two horizontal poles of that stator. One wire is
called the "start winding" and the other is called the "run winding".

In actuality, one end of start winding is connected to one end of the
run winding and so a schematic representation of that same electric
motor would look like this:

[image:
http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee11/IMAGES/MOTORS_FIG7.GIF]

And those three pins should be labeled "S" for start, "R" for run, and
"C" for common. The S pin will connect to a point on the top right
corner of the previous diagram, the R pin will connect to the bottom
left corner of the diagram and the C pin will connect to the top left
corner of the diagram where the start and run windings connect
together.

You should find that the resistance between the start pin and the common
pin added to the resistance between the run pin and the common pin adds
up to the resistance between the start pin and the run pin. And, you
are correct, there should be no continuity between any of the pins and
the motor housing.

The preceding discussion presumes that the motor in your dehumidifier is
a "split phase" motor that uses different kinds of wire for each
winding. One winding will use a large number of turns of very thin wire
whereas the other will use a much smaller number of turns of a very
thick wire. Because of the different impedances of those totally
different kinds of coils of wire, one kind of coil will develop it's
magnetic field earlier than the other when the same 120VAC 60 Hz voltage
sine wave is applied to them both. As a result of one winding
developing it's magnetic field earlier than the other, an observer in
the middle of the stator would see what appears to be a rotating
magnetic field. And, if that observer happened to be the magnetic
needle in a compas, it would rotate with that rotating magnetic field at
60 cycles per second, or 3600 rpm.

In fact, the way the electric motor depicted above would work is that
power would be applied to the TWO electric wires going to the motor.
The winding that uses many turns of thin wire would develop it's
magnetic field first, with the winding on one side of the stator being
North and the winding on the other side being South. Then, the winding
with fewer turns of thick wire would develop it's magnetic field with
the winding on one side of the stator being north and the winding on the
opposite side of the stator being south. Then the first winding would
reverse it's polarity so that the formerly south pole is now north, and
vice versa. And, then the same switch happens in the second winding.
and that whole sequence happens over and over and over again at a rate
of 60 times per second. So, a compass needle in the middle of that
stator would spin around and around, always pointing to which ever
winding happened to be north at the time.

After about a half a second, the motor gets up to about 3/4 of it's full
speed, and the centrifugal switch trips and cuts the start winding out
of the circuit so that the motor keeps turning on the run winding
alone.

NOW, normally the electric motors in air conditioners, fridges and
freezers need high starting torque, and you can get higher starting
torque by using a capacitor to cause the magnetic field of one winding
to develop earlier than the other, like this:

[image:
http://lh4.ggpht.com/_X6JnoL0U4BY/S1cIAHhcthI/AAAAAAAAHK4/ExTuYx05tis/tmp9C12_thumb4_thumb.jpg?imgmax=800]

That's because a capacitor is essentially just two plates that are close
together, and an electric voltage applied to one plate causes electrons
to be repelled and a tiny current to flow out of the OTHER plate.

In fact, if you apply a sine wave voltage signal to the first plate, the
current out the other plate will be at a maximum with the rate of CHANGE
of voltage in the first plate is at a maximum, and that actually happens
when the voltage sine wave's value goes from negative to positive or
from positive to negative. That is, the current out of a capacitor is
at a maximum when the applied sine wave voltage has zero value.

Similarily, when the current out the second plate will be at a minimum
when the rate of change of voltage in the first plate is zero, and that
actually happens when the voltage sine wave's value is at a maximum or a
minimum voltage. That is, current out of a capacitor is at a minimum
when the applied sine wave voltage is at a maximum positive or negative
value.

This, you can make both the start and run windings out of the same
number of turns of the same size wire if you put a capacitor in the same
circuit as one of the windings. That capacitor will cause the current
sine wave going into one of the windings to be 90 degrees out of phase
with the current sine wave going through the other winding. And, since
the magnetic field develops in lock step with the current through the
winding, one winding in a "capacitor start" motor will develop it's
magnetic field 90 degrees on the applied voltage sine wave earlier than
the other winding.

But, since that capacitor can't be serviced inside a hermetically sealed
motor, it's necessary to put the capacitor on the outside of the motor
so that it can be replaced if it ever goes bad.

There, now you know more about the basics of induction motor than 99
percent of home owners.




--
nestork

[Stormin Mormon]

No, it's not likely.

Sorry, meant to write NO!!!!! It's NOT likely!!!!!!

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.

<hrho...@sbcglobal.net> wrote in message news:6d797744-861a-426d...@b2g2000yqp.googlegroups.com...

[Stormin Mormon]

Dufas and I repair these things for a living. Dehumidifier compressor should have a cover on the side, which contains a start relay and an overload protector. These can be pulled off the electrical pins. None of the three pins should have continuity to the tin can, the copper tubing, or the electrical ground on the plug.

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.

"gregz" <ze...@comcast.net> wrote in message news:1724559198393389374.1...@news.eternal-september.org...

[Stormin Mormon]

Some have a relay, and no capacitors. Most have an overload protector on the common pin.

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.

"The Daring Dufas" <the-dari...@stinky-finger.net> wrote in message news:kpu1g8$k1h$1...@dont-email.me...

[jamesgang]

You've got a short. It's shot. The winding resistances are so low that a single short on any winding will look like all three connectors are shorted.

[gregz]

Trying to remember what was said in the book. I know the resistance is
suppose to be very high. A high resistance might be overcome with line
voltage. Any current from case to any terminal might be a better test, but
a short is a short.

Greg

[cotton...@yahoo.com]

On Thu, 20 Jun 2013 16:27:23 +0000 (UTC), gregz <ze...@comcast.net>
wrote:

Disconnect all three wires from the compressor, and read resistance
from the connectors on compressor to its case. Some times the short is
in the capacitor circuit or elsewhere. There should not be any reading
from the compressor's connectors to the case.

[Stormin Mormon]

Please make note of where the wires go. Not always easy to remember. This I know from experience. Digital pictures are useful.

.
Christopher A. Young
Learn more about Jesus
www.lds.org
.
.

<cotton...@yahoo.com> wrote in message news:39p8s8tnjpd7rlqkm...@4ax.com...

[Davej]

On Friday, June 21, 2013 4:41:17 PM UTC-5, Stormin Mormon wrote:
> Please make note of where the wires go. Not always easy to remember.
> This I know from experience. Digital pictures are useful.
>

Thanks all, the unit is indeed kaput.