Quiz 20

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

Trying to remove the drive assembly while it's still fastened to the shaft

An open winding in an electric motor means that________.

a wire in a winding is broken

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

Technician "A" is correct. Technician "B" is incorrect

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 in the run winding. Which of the following statements is correct?

Technician "A" is incorrect. Technician "B" is incorrect

A technician needs to check a single-phase compressor. He labels the three terminals "A" to "B", infinity from "B" to "C" and infinity from "C" to "A". Identify the terminals.

Cannot identify terminals: open winding

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

Check ohms and see if the top of the capacitor is bulging

T/F: Belt tension will not have any affect on the wear of the bearing.

False

T/F: If a resilient-mounted motor develops a short to the frame, the technician can simply cut the ground start wire as a permanent repair

False

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

False

T/F: Open windings will not affect the resistance of the start winding as well as the resistance reading between the Run and Start terminals

False

T/F: The electrical components for a fully welded hermetic compressor are checked at the disconnect box for the compressor unit

False

How can a technician tell if a belt is slipping?

If the tension of the belt is loose and if it can come off easily

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

It should move in a steady sweep, from zero, and bleed back to infinite

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

Replace the entire motor

T/F: Before testing a run or start capacitor with an ohmmeter, the capacitor should be discharged with a 20,00-ohm 5-watt resistor.

True

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

True

T/F: Pulleys must be in proper alignment or belt and bearing wear will occur

True

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

acts as an electrical resistance and causes the connection to heat more

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

all of the above

A megger ______.

measures very high resistances

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

motor will draw to much current while it is running

The leads of an ohmmeter using the Rx100 scale on the terminals of a capacitor and then reversed. The needle does not move. This would indicate that the capacitor is __________.

open

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

over tighten belt

Most electrical problems with an electric motor are_______.

short circuited windings

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

shorted

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

start

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

start switch

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

the capacitor can be shorted inside

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

trip a circuit breaker to shut off the unit

The recommended way to discharge a capacitor is to _______.

use a 20,000 ohm 5 watt resistor that has had insulated leads soldered to it