Deck 20: Troubleshooting Electric Motors

Question 1

Belt tension will not have any affect on the wear of the bearings.

Answer 1

False

Question 2

A technician needs to check a single-phase compressor. He labels the three terminals "A," "B," and "C" and takes resistance readings of the windings. He reads 10 ohms from "A" to "B," infinity from "B" to "C," and infinity from "C" to "A." Identify the terminals.

A) A: common B: start C: run
B) Cannot identify terminals: winding grounded
C) A: start B: run C: common
D) Cannot identify terminals: open winding

Answer 2

D

Question 3

If a resilient-mounted motor develops a short to the frame, the technician can simply cut the ground strap wire as a permanent repair.

Answer 3

False

Question 4

If the cost of repairing the motor is close to the cost of replacing the motor, it would definitely pay to repair the motor if the new component carries a one-year warranty and the repaired motor carries only a 90-day guarantee.

Question 5

The recommended way to discharge a capacitor is to ____.

A) place a screwdriver across the terminals
B) assume it will discharge itself over a period of time
C) use a 20,000 ohm 5 watt resistor that has had insulated leads soldered to it
D) use an ohmmeter

Question 6

Open winding will not affect the resistance reading of the start winding as well as the resistance reading between the Run and Start terminals.

Question 7

If a motor hums but does not start, there is a potential problem ____.

A) with the starting components
B) with an open winding
C) with insufficient supply voltage
D) all of the above

Question 8

If the resistance of the run winding is lowered, the imbalance in magnetic fields between the start and the run winding will be increased, and the starting torque of the motor will actually increase.

Question 9

What is the best method to repair a fractional horsepower motor that has bad bearings?

A) Replace the bearings.
B) Replace the bearings and shaft.
C) Add a capacitor to the circuit for added torque.
D) Replace the entire motor.

Question 10

Most electrical problems with an electric motor are ____.

A) short circuited windings, closed windings, and grounded windings
B) short circuited windings. open windings, and grounded windings
C) all of the above
D) none of the above

Question 11

The electrical components for a fully welded hermetic compressor are checked at the disconnect box for the compressor unit.

Question 12

Pulleys must be in proper alignment or belt and bearing wear will occur.

Question 13

If a condenser fan motor grounds out, it will usually ____.

A) trip a circuit breaker to shut off the unit
B) keep running as the current is only going to ground
C) run a little faster because the amperage draw will increase
D) cause the evaporator to ice up

Question 14

If the resistance of the run winding decreases, the ____.

A) motor probably will not start
B) motor will draw too much current while it is running
C) centrifugal starting switch will not start the motor
D) load on the motor is probably too great

Question 15

The wiring and connectors that carry the power to a motor must be in good condition. When a connection becomes loose, oxidation of the copper wire occurs. The oxidation ____.

A) has no effect on the electrical connection
B) acts as an electrical resistance and causes the connection to heat more
C) decreases the resistance
D) none of the above

Question 16

Before testing a run or start capacitor with an ohmmeter, the capacitor should be discharged with a 20,000-ohm 5-watt resistor.

Question 17

An open winding in an electric motor means that ____.

A) the winding is making contact with the motor frame
B) one winding is making contact with another winding
C) a wire in a winding is broken
D) the centrifugal switch to the start winding is open

Question 18

Technician "A" says that a shorted winding will result in an increased current flow through the winding. Technician "B" says that if a motor is to be replaced, a motor with a lower horsepower rating should always be used. Which of the following statements is correct?

A) Technician "A" is correct. Technician "B" is correct.
B) Technician "A" is correct. Technician "B" is incorrect.
C) Technician "A" is incorrect. Technician "B" is correct.
D) Technician "A" is incorrect. Technician "B" is incorrect.

Question 19

A megger ____.

A) is an ammeter that can measure very small amounts of current
B) is a digital voltmeter that measures very high resistances
C) measures high voltage direct current
D) measures very high resistances

Question 20

Technician "A" says that while checking the windings of a compressor, a reading of 10 ohms or less from the common terminal to ground indicates that the motor is okay. Technician "B" says that the resistance of the start winding should always be less than the resistance of the run winding. Which of the following statements is correct?

A) Technician "A" is correct. Technician "B" is correct.
B) Technician "A" is correct. Technician "B" is incorrect.
C) Technician "A" is incorrect. Technician "B" is correct.
D) Technician "A" is incorrect. Technician "B" is incorrect.

Question 21

The leads of an ohmmeter using the R x 100 scale are placed on the terminals of a capacitor and then reversed. The needle does not move. This would indicate that the capacitor is ____________________.

Question 22

How can a technician tell if a belt is slipping?

Question 23

If the needle of an ohmmeter used to check a capacitor goes toward the 0 ohms reading, stops and falls back to 20,000 ohms, what does this mean?

Question 24

What is a common mistake technicians make when trying to remove drive assemblies?

Question 25

If the needle of an ohmmeter used to check a capacitor goes to the 0 ohms reading and does not move, this would indicate that the capacitor is ____________________.

Question 26

A motor will not start when power is applied. If the belt is removed, the pulley spun, and power applied, and the motor continues to run, the first part to check is the _________________________.

Question 27

When the leads of an ohmmeter are placed on the terminals of a capacitor, what should the needle of the ohmmeter do?

Question 28

How can a technician determine if a run capacitor has overheated?

Question 29

Two common reasons for motor failure are improper pulley alignment and _________________________.

Question 30

A motor has four leads out of it: two red and two black. The resistance between the red leads is 3 ohms. The resistance between the black leads is 5 ohms. The black leads are connected to the ____________________ winding.