If a compressor motor is receiving the correct voltage but it refuses to run or it trips a fuse or circuit breaker, the problem might be that the motor windings have failed. The most common types of motor winding failures are:
1. An open winding is one in which the wire that forms the winding has separated or broken. A grounded motor is one in which the insulation around the winding wire has broken down and the copper wire itself is making electrical contact with some part of the motor casing
2. A grounded motor is one in which the insulation around the winding wire has broken down and the copper wire itself is making electrical contact with some part of the motor casing.
3. A shorted winding is one in which the winding insulation has failed, and one part of the winding is making unintended contact with another part of the winding.
Four ohm measurements are required to check the motor windings in a compressor. An ohm measurement must be taken between each pair of pins emerging from the casing .
If all show continuity (as they should), then take another ohm measurement between any pin and the compressor casing. It should read “infinite.”
The pin-to-pin readings should be something like two, six and 8 ohms, or four, 11 and 15 ohms. The highest reading should equal the sum of the other two because it is actually a reading of the two other windings in series.
The second-highest reading should be two to four times higher than the lowest reading (the start winding normally has two to four times as much resistance as the run winding). If one winding is open, two of the readings will be infinite. If any reading is zero, it indicates that a winding is shorted.
If the winding resistances are all reasonable, then you must take an ohm reading between any one of the pins and the casing ground. You’ll need to scrape off a bit of paint on the casing to ensure that you’re making good electrical contact between your ohmmeter probe and the metal of the casing. You’ll also need to make sure that your ohmmeter is set on the highest ohm range available.
If you get an infinite reading, the motor is not grounded to the casing. It is not necessary to check the other pins, because you have already determined that the pins are continuous with each other. If any winding is grounded, all three pins will show a less-than-infinite reading to the casing. Checking compressor motor windings (three phase)
“Ohming” out the windings on a three-phase motor is even easier than on a single-phase motor. The pin-to-pin resistances should all be equal. They may be quite low (maybe one-half ohm or less). Be careful not to jump to the conclusion that just because the winding resistance is very low, that the windings are shorted. The three-phase motor windings are checked to the casing ground in the same way as a single-phase motor.
Motor wiring color codes
1. An open winding is one in which the wire that forms the winding has separated or broken. A grounded motor is one in which the insulation around the winding wire has broken down and the copper wire itself is making electrical contact with some part of the motor casing
2. A grounded motor is one in which the insulation around the winding wire has broken down and the copper wire itself is making electrical contact with some part of the motor casing.
3. A shorted winding is one in which the winding insulation has failed, and one part of the winding is making unintended contact with another part of the winding.
Four ohm measurements are required to check the motor windings in a compressor. An ohm measurement must be taken between each pair of pins emerging from the casing .
If all show continuity (as they should), then take another ohm measurement between any pin and the compressor casing. It should read “infinite.”
The pin-to-pin readings should be something like two, six and 8 ohms, or four, 11 and 15 ohms. The highest reading should equal the sum of the other two because it is actually a reading of the two other windings in series.
The second-highest reading should be two to four times higher than the lowest reading (the start winding normally has two to four times as much resistance as the run winding). If one winding is open, two of the readings will be infinite. If any reading is zero, it indicates that a winding is shorted.
If the winding resistances are all reasonable, then you must take an ohm reading between any one of the pins and the casing ground. You’ll need to scrape off a bit of paint on the casing to ensure that you’re making good electrical contact between your ohmmeter probe and the metal of the casing. You’ll also need to make sure that your ohmmeter is set on the highest ohm range available.
If you get an infinite reading, the motor is not grounded to the casing. It is not necessary to check the other pins, because you have already determined that the pins are continuous with each other. If any winding is grounded, all three pins will show a less-than-infinite reading to the casing. Checking compressor motor windings (three phase)
“Ohming” out the windings on a three-phase motor is even easier than on a single-phase motor. The pin-to-pin resistances should all be equal. They may be quite low (maybe one-half ohm or less). Be careful not to jump to the conclusion that just because the winding resistance is very low, that the windings are shorted. The three-phase motor windings are checked to the casing ground in the same way as a single-phase motor.
Motor wiring color codes
