120 Unit 20 Review

The black leads are connected to the _____ winding.

• start

• run

• open

• shorted

A motor will not start when power is applied. The belt is removed, the pulley spun, and power is applied, and then the motor continues to run. What should be checked next?

• Motor bearings

• Motor shaft

• Starting switch

• Run capacitor

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: common; B: start; C: run

• Cannot identify terminals: winding grounded

• A: start; B: run; C: common

• Cannot identify terminals: open winding

A technician suspects the belt in a motor is slipping and notices the pulley has a polished, mirror-like finish. What is the recommended action?

• Tighten the belt and replace the pulley.

• Clean the pulley.

• Replace the pulley and lubricate the belt.

• Replace the motor.

An open winding affects the resistance reading of the start winding but not the resistance reading between the Run and Start terminals.

• True

• False

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

• True

• False

Belt tension will have no effect on the wear of the bearings.

• True

• False

Compared with open motors, hermetic compressor motors _______.

• have no electrical components to test

• are easier to diagnose because of their simple enclosure

• are harder to diagnose because they are enclosed in a shell that dampers motor sound

• are prone to types of motor failure that rarely affect open motors

How can a technician tell if a belt is slipping?

• The motor runs for short periods but then shuts off.

• Airflow is increased through the air distribution system.

• Motor bearings wear out prematurely.

• A low force reading on a belt tension gauge indicates that the belt is too loose.

How can moisture accumulation in an open motor affect ground readings?

• A slight ground circuit may occur.

• Resistance to ground increases.

• Instruments measuring ground resistance become less accurate.

• Moisture has no effect on ground readings.