Unit 20 Troubleshooting Electric Motors

electrical, mechanical, appear, Technicians

Motor Troubleshooting

Problems are either ________________ or _________________

Mechanical problems may ______________ to be electrical

__________________ must be able to diagnose system problems correctly, and locate the cause of the problem, which is not always the resulting effect

Most common problems involve the

Mechanical Motor Problems

_________________________________ bearings of the shaft where the drive is attached

Bearing failure

Mechanical Motor Problems

Tight or worn bearings

Lack of lubrication

Excessive grit in the bearing

Overtightened belts

Not often repaired by the field technician

Pulley, coupling, fan wheel

Remove Drive Assemblies

___________, _____________, or ______________ must be carefully removed from the shaft

Special

Remove Drive Assemblies

__________ pulley pullers can be used

shaft

Remove Drive Assemblies

Set screws are tightened to the _________

damage

Remove Drive Assemblies

Trying to drive the motor shaft out of the assembly can ______________ the shaft

Overtightened

Belt Tension

_______________________ belts damage bearings

slippage

Belt Tension

Loose belts can result in _________________

Belt tension gauges

Belt Tension

___________________________ should be used

aligned, damaged, straightedge, small motors

Pulley Alignment

Drive and driven pulleys should be ______________

Drive mechanisms can become ___________________

May be aligned with the help of a ___________________

Certain amount of adjustment tolerance is built into ____________________

Easier

Electrical Problems

_____________ to diagnose

burned

Electrical Problems

Motor may smell ______________

Common motor problems include:

Electrical Problems

Open motor windings

Short circuit from winding to winding

Short circuit from winding to ground

ohms

Open Windings

Can be detected with the ___________ function on a digital multimeter

resistance

Open Windings

Should be a known, measurable __________________ from terminal to terminal

open, run, start

Open Windings

The ___________ winding would affect the resistance reading of the start winding

Would also affect the resistance reading between the _______ and ________ terminals

Alternative, increases, run, start

Shorted Motor Windings

Results from holes in the winding insulation

___________________ path for current is created

Current flow through the winding ____________________

If the short is in the _______ winding, the motor may start, but the current draw will be high

If the short is in the __________ winding, the motor may not start, but excessive current will be drawn

continuity, Megohmmeters (meggers), ground, refrigerant oil

Short Circuit To Ground (Frame)

Should be no _________________ from a winding to ground

_______________________________ can be used to detect small, high resistance paths to ground

In damp conditions, dirty motors have a resistance reading from windings to _______________

If _____________________ is dirty, hermetic compressors may have resistance readings from a winding to ground

easy, full power

Single-Phase Motor Starting Problems

Relatively __________ to troubleshoot

Check for ____________ to the motor

Symptoms of starting problems

Single-Phase Motor Starting Problems

Motor hums, then shuts off

Motor runs for short periods and shuts off

Motor will not try to start at all

electrical circuits

Single-Phase Motor Starting Problems

If motor turns freely, check ___________________________

starting components

Single-Phase Motor Starting Problems

If motor hums but does not start, the __________________________ should be checked

digital multimeter, Discharge

Checking Capacitors

Capacitors can be checked with a _______________________

____________________ capacitor before testing

Formula for a run capacitor under load:

Checking Capacitors

(Start Winding Amperage x 2652)/Voltage

When testing a capacitor without a load:

Checking Capacitors

Connect one lead to each terminal

Check dual capacitors on both sides

Remove bleed resistor before testing

Run capacitors

Capacitor Identification

Encased in metal; oil-filled

Swollen capacitors should be replaced

Start capacitors

Capacitor Identification

Dry type, encased in a shell of paper of plastic

May have a bulge in the vent at the top of the container if exposed to overcurrent

Should be changed

good, Loose, electrical contacts, resistance, heat generated, low voltage, amperage

Wiring and Connectors

Wiring must be in ___________ condition

____________ connections can cause problems

Can result in oxidation on ________________________

Oxidation increases circuit ____________________

Resistance increases the amount of ___________________

Can result in ______________________ being supplied to the motor

Low voltage can result in increased motor ______________________

outside

Troubleshooting Hermetic Motors

Can only be checked electrically from ______________ the compressor shell

Experience the same problems as open motors

Troubleshooting Hermetic Motors

Grounded circuit

Open circuit

Short circuit

Starting component problems