This will always be the case.įor a short to ground situation, you can put a lead on one of the three terminals and the other on a bear metal point on the motor housing. For single phase motors, the relationship is R1 + R2 = R3.
Take the first reading and lets call that one R1, the second reading R2, and the third reading R3. The readings will be interrelated in such a way that you will know a problem exists if the relationship is not correct. Changing the meter to the white and red leads will give you a third reading. Changing the leads to the black and red will give you a second reading.
Connecting a resistance meter from the black to the white leads should give you a resistance reading. Second is a disconnected short, and third is a short to another lead.Ī motor that has not failed has a measurable resistance that will always be true for operational motors. There are three ways for the motor to fail electrically. We will discuss the electrical failing here. Inside the motor, all three wires are connected and you can run a circuit by using any combination of two of the three wires.ĭetermining a motor with an electrical problem: A motor can fail either mechanically or electrically. The black and red wires run a different winding and also create a resistance measured in amperes. The black and white wires connect forming a circuit and the motor winding in this circuit creates a resistance measured in Amperes. In this explanation I am going to stick with red for simplicity. Sometimes this wire can be brown, yellow, blue or another color depending on the manufacturer.
The black and white wires are the normal L1 and L2 from your power source. The wires run to the motor are the black, wh ite and red. In this figure we show a typical single phase motor. What I will explain here will apply to both situations. Residential systems run off a single phase electrical system either with one (125V) or two legs (250V). There are three major motors used in an air conditioning system: the compressor motor, the outdoor fan motor, and the indoor blower motor.
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