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.
If any of the pins show continuity to the can, the coils are shorted and compressor is bad. ^_^
TDD
Thanks.
If any of the pins show continuity to the can, the coils are shorted and compressor is bad. ^_^
TDD
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!!!
Any experts here ? I don't see many good answers.
Greg
One of several on youtube, this is for a 220V system
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
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: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: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: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.
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!!!
Any experts here ? I don't see many good answers.
Greg
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
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.
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
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.
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.
Thanks all, the unit is indeed kaput.
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