Elect Comp 1

7/27/2019 Elect Comp 1

1/13

REF and AIRCON FUNDAMENTALS Page 4 of 12Academic Year 2004 2005, Semester 1Prepared By: Nolasco K. Malabago, Ph.D

RAC ELECTRICAL COMPONENTS:Motor Compressor and its Accessories

I. Terms and Definitions

Calibrate to adjust a meter so that the needle is properly aligned tothe proper set point on the scale.

Contactor magnetic re lay switch which usual ly opens and c loses aline voltage circuit actuated by a control circuit magnetic coil.

Continuity complete circuit in which current can flow.

Control relay e lectromagnetic switch that controls a l ine voltageload by means of control voltage.

Current relay (Coil type) motor starting relay that disengages thestar t winding af ter the compressor reaches 75% of i ts ratedspeed; used on fractional horsepower motor.

Current relay (Hot wire type ) motor starting relay that disengagesthe start winding by the movement of a thermal wire; used onsmall fractional horsepower motor.

Full Load Amperage (FLA) total current the device draws when it isrunning fully loaded.

Infinity (Infinite Resistance) the extreme end of the ohmmeterdesignated by .

Line Voltage main power supply

Locked Rotor Amperage (LRA) the current drawn by a motor whennot running but supplied with power.

Potential relay motor start ing re lay that operates off of the backEMF generated in the start winding; used pr imari ly on hp orlarger motor compressors.


2/13


Probes insulated ends on test instruments leads that are held whilechecking the circuit.

Relay an electromagnetic switch.

Sol id state relay a the rmal -sensi tive motor s tart ing swi tchconstructed from a ceramic material encased in a nonflammable

covering.Time delay relay provides a predetermined interval between

operations of a device.

Range limits of a particular portion of a meter.

Example: 230 VAC (volts alternating current)-this range would bealr ight to use for any AC voltage 1 to 230; anything over woulddamage the meter.

Zeroing the ohmmeter to al ign the meter needle over zero on theohm scale.

II. Safety Rules in Testing Electrical Circuit

1. Stand on dry, non-conductive surfaces when test ing l ive c ircuits.

2. Be sure the power is off when checking a circuit with an ohmmeter.

(Note: an ohmmeter could explode if it came in contact with line

voltage.)

3. Do not use meter leads with defect ive probes.

4. Do not have both hands in a h igh vol tage cabinet .

(Note: Clip one voltmeter lead on and then take the other lead and

check the circuit.)

5 . Do not touch metal cabinet or other grounded materia l.

6 . We ar eye pro tec ti on .

7. Use fuse pullers (i f needed on the t rainer).

8 . Do not work on live ci rcui ts alone.

9 . Do not assume that the power is OFF.

10. Discharge capacitors with a bleed resistor

before removing or testing.

III. General Rules for Protection of the Tester

1. Keep c lean and dry .

2. Avoid exposure to high temperature.


3/13


3. Use only for intended purpose.

4. Use within meter range l imits.

5. Set meter in highest range pr ior to taking readings.

6. Follow directions on specif ic operating instructions.

IV. Meter Applications

1. Voltmeter Measures l ine voltage

Measures voltage drop at

the load

Measures low voltage

Indicates opencomponents

2. Ohmmeter(Caution: Be sure allpower is off beforechecking an electricalcircuit with anohmmeter.)

Checks fora path for current flow

(continuity)

Checks for resistance to current flow

Determine motor windings and terminals

Checks for shorts and grounds

Checks capacitor

(Caution: Be sure that the charge is bled off before checking.)


4/13


3.

3.

3.

3.

3 . Ammeter Checks starting amperage

Checks running amperage

Checks locked rotor amperage

4. Circuit Conditions

4.1. Open Circuit

Most frequent circuit problem No path of current

Voltmeter will indicate voltage across open

Caused by

Pitted Contacts

Defective relay coil

Broken wire

Blown fuse

Tripped circuit breaker

Open switch

4.2. Short Circuit

Second most frequent circuit problem


5/13


Electrical circuit that has a lower resistance than intended

Indications

Blown fuse

Tripped circuit breakers

Melted wires

Swollen run capacitors

Blackened terminals

Burnt case

(Example: Touching a screw driver to a current carrying

conductor and at the same time against the side of

appliance cabinet would result in a blown fuse, a badly

burnt screwdriver, a burnt spot on the cabinet and

possible personal injury)

4.3. Grounded Circuit

A high resistance path that current may take to a common

ground

May be caused by a blown fuse or tripped circuit breaker

May be determined with an ohmmeter

V. Servicing and External Testing of Hermetic Motor CompressorUsing Continuity Tester

1. Servicing Electric Motors

The maintenance, troubleshooting, removal, repair and installationof electric motors as well as their accessories is a major portion of aservice technicians job.

Such person must know how to use instruments and beknowledgeable about electricity to accurately determine the trouble.

It is important that a solid base be provided for the installation ofany motor and that it be bolted down securely.

The armature shaft should be leveled for a horizontal motor andexactly vertical for a vertical motor.


6/13


If the motor is severely damaged and must be replaced, thefollowing information must be taken:

a ) type o f moto rb) operating line vo ltagec) maximum current draw

d) direction of rotation and speede) mount ing hardware

Use the manufacturers nameplate to get all the required motorspecification as the original motor.

The replacement motor may have a maximum current draw of 10%larger, but never less than the motor being replaced.

Approximate amperage rating for smallhermetic motors @ 220 240 VAC

HPRating

Full Load Locked Rotor

1/6 2.2 13.21/4 2.9 17.41/3 3.6 21.61/2 4.9 29.43/4 6.9 41.41 8.0 48.0

1 1/2 10.0 60.02 12.0 72.03 17.0 102.0

2. Motor Lubrication

Open motors may be lubricated in various ways. It depends on thetype of bearing used and the position of the motor. Open motorsusing bronze bushings, plain or sleeve may be lubricated in twodifferent ways:

a ) W ick sys temb) S lip ring system

The wick system uses a well or reservoir in the end bell. A wick(cotton or wool yarn ) carries oil from this well to the shaft andbushing.

This system allows long interval between servicing bearings andprevent the bearing from getting too much oil .

If the bearing is to be removed from the shaft, the yarn should belifted clear of the bearing to prevent it from being forced betweenthe shaft and the bearing upon replacement.


7/13


Wick lubricated bearing s hould be oiled one or two dropsevery six months using medium viscosity (200 300 viscosity) ,no detergent oil such as SAE 20 or 30.

3. Cleaning Motors

a) Dust and l int in the motor wi l l prevent proper air circulation.b) Compressed air or hand bellows should be used to blow the

dirt out.c) Any oi l which may overflow from the bearing should be wiped

off.d) I f the motor must be dismantled, all parts should be careful ly

cleaned before being worked on or reassembled.

4. Servicing Fan Motors

The common fan motor troubles are:

a ) loose connectionb) dry bea ringc ) worn bea ringd) burn out motore ) l oo se fanf ) out -of -ba lance fang) fan blades touching the housing

Loose or dirty connections will cause too much voltage drop at the motor and the fan motor wil l lose speed, hum loudlyand

overheat.

To check, use sensitive ohmmeter and dont rely on visualinspection.

A dry bearing will cause the same symptoms but wil l last for ashort period of time before the bearing wil l seize (bind) or becomebadly worn.

A rattle in the fan motor may sometimes be nothing more than aloose fan on the motor shaft.

This noise can be remedied by tightening the set scre w that

fastens the fan hub to the shaft.

If the fan blade touches the fan housing, the motor may be out ofl ine or the shroud or housing may be bent.

It can be remedied by moving the fan on the shaft or moving theshroud or housing.

Do not bend the fan blades. It will cause the unit tovibrate.


8/13


5. External Testing of Hermetic Motors

In diagram A ,The starting winding is being checked for continuity. I f the bulbl ights on, i t means that the current is f lowing through the start ingwinding f rom S to C . In thi s case, there i s no open spot in thewindings.

In diagram B ,The windings are being checked for grounds. Grounding meansthe same part of the internal wiring or the terminals are touchingor making electrical contact with the metal parts of the unit.

I f the bulb l ights on when one of the electrical lead is touched toany of the terminals and the other lead is touched to the clean orbare metal body of the dome, it means that the current is f lowingalong the internal wires and through a grounded wire into themetal. Be sure that the terminals are c lean and dry dur ing thetest; it might be temporarily grounded by dirt .

In diagram C ,The continuity of both the running and starting windings arebeing checked.

In diagram D ,The running winding only is being checked for continuity.

Any shorting of the motor winding wil l increase the current draw,dec re ase power and ove rheat the uni t. ( a sho rted c irc ui tsometimes be detected by an interruption in the steady hum ofthe motor when it is running).


9/13


VI. Identifying the Run (R), Start (S), and Common (C) Terminalsof Single - Phase (1PH) Hermetic Compressor

Terminals of Hermetic Compressors can be:

Screw Type

Screw and Lock Quick Connector Type

Usually, a s ingle phase electr ic motor have two mainwindings for s tarting and operat ion. The terminals areconnected as follows:

One end is connected to run windings

One end is connected to start windings

The third terminal is common lead to both windings

STEPS1. Draw the picture of the terminal on a piece of paper (which may

be in these forms).

2. Take the readings by pair ing the two leads.

Result:

The pair with the highest resistance reading is the

start and run.

The pair with the higher resistance reading is thestart and common.(this identifies the lighter gagehigher resistance wire of start winding )

The pair with the lowest resistance reading is runand common.

3. Examplea b c

a-b =8Wa-c =12Wb-c =4W

From the paired terminal readings:

...the pair with the highest resistanceis a-c, so b is the common terminal(label it C).

.. .the pair with the lowest resistance isb-c, therefore c is the run terminal (label it R).

...the remaining terminal is (a)which is the start terminal (label it

S).


10/13


VII. Electrical Symbols

VIII. Wiring Diagrams

Why Use a Diagram?

Most e lect ri ca l p roblems can be d iagnosed with the a id o f a

wiring or schematic diagram.

The diagram serves as a road map to the electrical connections of

the appliance and, l ike any map, must be studied before the best

route to proceed can be determined. L ike a conventional roadmap, the appliance diagram will help identify the different routestha t c ur ren t c an take, i den ti fy point s o f i ntere st ( ci rc ui tc omponen ts ), and p rovide impor tant i nformation suc h asresistance values and the colors of different wires.

I t' s impossible to describe and l ist every new component and

i l lustrate every method of depic t ing i t . One reason for th is isthat,


11/13


appliance technology is changing rapidly;

there are far too many manufacturers to fu lly representthem all in the manual.

Wiring versus Schematic Diagrams

Schemat ic d iagram. The more commonly used are ladderschematic because

The components are laid out in a stacked, straight l inemanner, much like the rungs of a ladder.

Of all the types of diagrams available, this type is probablythe easiest to read and understand.

The ladder diagram is preferred over the wiring diagram fortroubleshooting purposes.

Schematic Diagram of aRefr igerator

Wiring Diagram of a


12/13


Wiring diagram. This type has dist inct advantages of over aschematic.

Each separate wire is shown along with its color.

Mult iple connection points, such as the terminal block onthe defrost timer (circled above) are readily apparent. Thisfeature makes replac ing the t imer much easier s ince thew ires c an be r ec onne cte d by w ire c olor and te rminalnumber.

Termination point for each wire is shown thus, tracing aparticular wire is also simplif ied.

As a general rule, each type of diagram has its purpose.

For component t roubleshoot ing purposes, the schemat icworks best.

The wiring diagram simplifies locating and replacing parts

or locating breaks in wires.

In most cases, on ly one type of d iagram is suppl ied by themanufac tu re r so, r egardless o f which i s ava il ab le , thetechnic ian must be able to use e i ther with some degree of competency.


13/13


Documents

Elect Comp 1