Servicing & Maintaining Window-Type AC and Domestic Ref Units

FANS

Fans are used extensively in air conditioning and refrigeration units for moving or circulating air
over air cooled condensers and evaporators coil. The function of a fan is to increase the
pressure of air which it handles by converting into pressure, the relative velocity of air with
respect to the blades at the entrance. Fans are often designated as booster, blowers or
exhausters. As considered here, a booster is a fan with ducts connected to both inlet and
discharge; a blower has discharge duct only and exhauster has an inlet duct only.

TYPES OF FANS

Fans are identified into two general groups:

1. Centrifugal – in which air flows radially through impeller.

Forward curved blade Backward inclined blade Radial blade

2. Axial flow – in which air flows axially through the impeller.

Propeller Fans

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Sirroco Fans

Propeller fan with slinger ring for spatters or
“sling” that throws droplets of water onto the
hot condenser.

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ELECTRIC FAN MOTOR

An electric fan motor is a mechanical device that converts electric energy into mechanical
motion. In an electric motor, electricity is used to produce magnetism. The magnetism is used to
turn a shaft, and the turning shaft is used to do work.

Electric motors are the most popular and
common type used for providing mechanical
power for air conditioning and refrigeration
system. They are popular because they are
readily available with the use of electricity and
their motors are simple.

MAJOR PARTS OF ELECTRIC (FAN)
MOTOR

1. Frame – the part that holds everything
together. It includes the end bell, outside
enclosure and the bearing or bushing.

2. Stator – the stationary part of the motor. It
includes the field coils (winding).

3. Rotor (armature) – the revolving part of the
motor. It includes the shafting.

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JOB SHEET #4

IDENTIFYING THE TERMINAL LEADS OF 3-SPEED FAN MOTOR USING A
VOM (Volt-Ohm Milliammeter)

OBJECTIVES: After completing this Job Sheet, you should be able to:

- identify the terminal leads of a 3-speed fan motor using a VOM (Volt-Ohm-
Milliammeter).

EQUIPMENT, MATERIALS, AND AIDS YOU WILL NEED

QUANTITY UNIT DESCRIPTION
1 unit Multimeter VOM (Volt-Ohm-
Milliammeter)
1 unit 3-Speed fan motor
1 roll Plastic electric tape
1 pc. Paper
1 pc. Pencil or ball pen

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Introduction:

Terminal leads of fan motors are identified by color-coding and by the resistances of the
windings. The colors of the terminal leads may fade, making them hard to identify. The terminal
leads may have to be identified by the resistances of the windings.

Steps in identifying the terminal leads of a 3-speed fan motor using. a VOM:

1. Label the terminal leads from 1 to 5 as shown in Figure 1. Use a masking tape.

Figure 1.

TERMINALS RESISTANCE RANK
(OHMS)

1 1&2

2 1&3

2. Make a table like the one shown 3 1&4
on the right to record the 4 1&5
resistances of the different 5 2&3
terminal lead combinations. 6 2&4

7 2&5

8 3&4

9 3&5

10 4 & 5

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3. Set the multimeter at R x 1. Measure and
record the resistances of the different
terminal leads. Use the table prepared in
Step 2.

NOTE:
Adjust first the VOM to zero reading before
taking any resistance reading.
Countercheck the values or resistances
(Figure 2).

Figure 2

4. Rank the readings from highest to lowest,
making the highest reading as rank 1 and
the lowest as rank. 10.

Figure 3 illustrates diagramatically the
windings of a 3 -speed fan motor.

Figure 3: Windings of a 3-speed fan motor

Characteristics of the Windings
Terminal:
A and C - highest resistance
A and L - second to the highest
H and M - is equal to M and L
C and H - higher than H and M or M and L

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5. The terminal lead found both on the highest (Rank 1) and second highest resistance (Rank
2) is the auxiliary terminal lead.

NOTE:

If there is no terminal lead found on both the highest and second highest resistance, check
the values by measuring the resistance of the terminal leads again.

a. With the auxiliary terminal lead now identified, the other terminal lead on the highest
reading (Rank I) is the COMMON terminal lead.

b. The other terminal lead on the second to the highest reading (Rank 2) is the LOW
terminal lead.

6. Using the LOW terminal lead now as the reference point, measure the resistance of the two
remaining terminal leads.

a. The one with the higher resistance is the HIGH terminal lead.

b. The other unidentified terminal is the MEDIUM terminal lead.

7. Using now the LOW terminal lead as the reference point, measure the resistance of the
other terminal leads.

NOTE:

If the terminal leads are identified correctly, they must follow the table below.

Terminals

L and A - highest resistance

L and C - second highest resistance

L and H - second lowest resistance

L and M - lowest resistance

NOTE:

If the readings of the resistances do not follow the pattern above, repeat identifying the
terminal leads.

Assignment

After carefully studying the step-by-step procedures of identifying the terminal leads of a 3-
speed fan motor using a VOM (Volt-Ohm-Milliammeter), ask for the materials and tools from the
instructor. Practice the skills required until you have gained mastery.

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SELF-CHECK #4

CALL YOUR INSTRUCTOR who will observe you perform the steps in identifying the terminal

leads of a 3-speed fan motor using a multimeter (VOM). He will also evaluate your performance
using the Instructor’s Checklist.

Instructor’s checklist Acceptability
Yes No
1. Checked if terminal leads have labels. ______ ______
2. Checked if VOM is adjusted at zero adjustment. ______ ______
3. Checked if terminal leads are ranked correctly. ______ ______
4. Checked if terminals are ranked correctly. ______ ______

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JOB SHEET #5
CLEANING FAN MOTOR AND FAN BLADE

INTRODUCTION
All fans that move air accumulates dirt particularly on the fan blades and motor. Such dirt
reduces the efficiency of the fan. To maintain proper operation of the fan, the dirt should be
removed regularly.
Steps in cleaning fan motor and fan blade:
1. Disconnect lead wires of the motor and

remove the fan blade from the motor shaft.

2. Remove the motor cradle bolts/screws
holding the fan motor.

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3. Lift the motor up and out and proceed to
clean the fan motor and blade.

4. Remove dirt and grease from the housing
of the motor.

5. Check the sleeve bearings by moving the
shaft up and down. If the movement is
excessive, the bearings or shaft may be
defective.

6. Mark the end plates of the motor with a
permanent pen or a punch before
disassembling it.

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7. Loosen and remove the end plate screws
and bolts.

8. Remove the end plate by prying it from the
casing without using excessive force.

9. Remove the rotor. Make sure that the
windings in the rotor and stator are not
damaged, dented or scratched.

10. Soak the stator windings in motor cleaner
for about 5 minutes.

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11. Use a paint brush to remove dirt and
grease from the stator assembly.

12. Rinse the stator assembly with fresh
motor cleaner. Allow to dry.

13. If all the motor parts are found to be in good condition, you may then assemble the motor.

1. housing
2. plate
3. rotor
4. end plate
5. bolt
6. bolt

CLEANING FAN BLADE

1. Remove the surface dirt and grease from
the blade.

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2. Apply cleaning solution to fan blades then
wait for about 5 minutes. Clean stubborn
spots with smooth sandpaper.

3. Rinse the fan blade in water.

REMOVING AND REPLACING DEFECTIVE
SLEEVE BEARINGS

1. If the shaft can be moved vertically, it
indicates a worn bearing, a worn rotor
shaft, or a worn bearing housing.

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NOTE: A loose rotor shaft may cause the
rotor to rub on the stator core and cause
the windings to overheat and short.

- A defective sleeve bearing

2. If the sleeve bearing is defective, then proceed as follows.
3. Remove the cup cover containing the

sleeve bearing.

4. Remove the lock washer of the sleeve
bearing.

5. Force the bearings out of end plates using
the proper bearing extractor.

6. Remove all retainers.

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7. Place the new sleeve bearing on the
extractor and press the bearing into the
end plate.

8. Return the oil retainer, lock washer and the end cap then reassemble the motor.
REMEDYING EXCESSIVE SHAFT END
PLAY.
1. Disassemble fan motor.

2. Insert or add two fan shaft washers to both
shaft ends.

3. Assemble again and test if there is any
more shaft end play.

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SELF-CHECK #5

CALL YOUR INSTRUCTOR to ask you to carry out a number of exercises in fan blade and
motor repair. He will observe you and check you according to the criteria stated below. You
have 45 minutes to complete this exercise.

Instructor’s checklist Acceptability
Yes No
1. Selection of instrument and materials ______ ______
2. Use of tools ______ ______
3. Detection of defective sleeve bearing ______ ______
4. Disassembling of fan blade and fan motor ______ ______
5. Assembling fan motor ______ ______
6. Cleaning of fan motor and blade ______ ______
7. Detection of excessive shaft end play ______ ______
8. Removing and replacing of defective sleeve bearing ______ ______

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Learning Outcome #4 : Service Electrical Power and
Control Circuit

Assessment Criteria:

 Proper electrical tools and test instrument are used in checking power supply and
electrical controls and wiring conditions

 All electrical controls, wiring, power supply are checked and inspected

 Loose connections and other wiring defects are reported

 Defective controls and wiring are repaired / replaced in line with standard operating
procedures.

Resources:

Equipment and Materials:

You should be provided with the following:

1. Electrical tools and test instrument
2. Set of screwdrivers
3. Electrical pliers
4. Multitester
5. Clamp ammeter
6. Electrical wire
7. Electrical tapes
8. Window-type air conditioning unit
9. Refrigeration unit

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LEARNING EXPERIENCES

LEARNING OUTCOME NO 4: Service Electrical and
Control Circuit

Learning Activities Resources
 Operation Sheet #1
1. Read Operation Sheet “Checking
Electrical Connections and Controls”

2. Do the Self-Check.  Ask your trainer/instructor to provide you
with set of tools and instrument for you to
execute a Performance Test. Your
instructor will record your proficiency by
using the checklist provided.

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OPERATION SHEET #1
CHECKING ELECTRICAL CONNECTIONS AND CONTROLS

OBJECTIVES: After completing this Operation Sheet, you should be able to:
- check electrical connections for tightness; and
- check electrical controls for normal operations.

EQUIPMENT, MATERIALS, AND AIDS YOU WILL NEED

QUANTITY UNIT DESCRIPTION
1 unit Multitester (UDM)
1 unit Clamp-On Ammeter, 300 Amps.
1 set Screw drivers
1 set Open-end wrenches

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CHECKING ELECTRICAL TIGHTNESS
INTRODUCTION:
Short, open and loose connections in refrigeration electrical circuits are the primary causes of
failures and breakdown. An open circuit will render a refrigerator totally inoperative. A short
circuit will blow out the fuse while loose connections will cause intermittent operation, and most
probably a burned motor compressor. Checking of the different electrical components and
circuits is necessary to locate the trouble and select the remedial measures to be applied.
Steps in checking electrical tightness:
1. Compressor terminal block. Check the

terminals to see if the screws are
tightened properly by using the
appropriate wrench, as shown.

2. Check the plug connection for tightness by
using a screw driver.

CHECKING ELECTRICAL CONTROLS FOR NORMAL OPERATION
1. Continuity test is shown.

- If the tester registers an infinite reading,
it means motor winding is good.

- If no reading is indicated, the motor
winding is open.

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2. The thermostat continuity test is shown.

- At R x 1, no reading means thermostat
is good.

- At R x 5 or 10, with reading means
thermostat is good.

- At R x 5 or 10, slowly turn the tester
knob to zero if tester point does not
deflect and remains in maximum
reading, it means thermostat is open or
shorted.

3. The overload protector test is shown.

- If tester registers an infinite reading, it
means overload protector is good.

- If tester does not register any reading,
overload protector is open or shorted.

4. The starting relay test is as shown.

- If tester registers an infinite reading, it
means starting relay (overload
protector) is good.

- If tester does not register any reading,
starting relay (overload protector) is
open or shorted.

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5. The motor compressor test is shown.
6. The clamp ammeter test is shown.

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CHECKING POR OPEN/SHORT (CONTINUITY TEST)
1. Set the multitester to range R x 1.

NOTE: Refer to L.E. “Using the
Multimeter/ VOM” if necessary.

2. Apply a teat prod to the tip of the plug of
the refrigerator.

3. If the circuit is open or shorted, no
resistance reading will be noted on the
tester, as shown.

4. If the circuit is not open or shorted, a
resistance reading will be noted at the
tester dial.

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CHECKING THE THERMOSTAT CONTROL
1. Connect the test prods to the terminal, as

shown.

2. A good thermostat control will register zero
or no resistance.

3. If resistance is registered on the tester dial
as shown, the thermostat is shorted and
will have to be replaced.

CHECKING THE OVERLOAD PROTECTOR
1. Connect the test prods to the terminals of

the overload protector, as shown.

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2. A good overload protector should indicate
a zero reading.

3. If resistance is registered on the tester dial
as shown, the overload protector is shorted
and will have to be replaced.

CHECKING THE MOTOR COMPRESSOR
1. Connect the test prods to “C” common and

“R” running term, as shown.
- CR with continuity
- CS with continuity
- RS without continuity
2. A reading of between 10 to 50 ohms
should register.

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3. Any part of the compressor terminals
should not indicate any resistance reading
with respect to the body chassis of the
compressor. If reading is registered, then it
is grounded.

AMMETER TEST
1. Plug-in the refrigerator, as shown.

2. Clip the clamp ammeter to one side of the
line cord.

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3. If ammeter reading is higher than the
normal ampere rating of the motor
compressor, the internal winding is
shorted. Rewind or replace the compressor
motor.

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OPERATION SHEET #2

OVERLOAD PROTECTOR: TYPES, PARTS AND OPERATING PRINCIPLES IN A
REFRIGERATING SYSTEM

OBJECTIVES: After completing this Operation Sheet, you should be able to:
- explain the operation of an overload protector; and
- identify the parts of an overload protector.

MATERIALS, AND AIDS YOU WILL NEED
- Charts
- Transparencies
- Trainer

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INTRODUCTION

Overload protector is in series with the running and starting winding. Overload protector allows
an excessive current for a very short time (about 3 to 4 seconds - approximate time for the
motor to start. It will break the circuit of the high current flows lasts for any length of time (5
seconds or more) As shown in figure 1.

Figure 1. Wiring Diagram

A. External Overload Protector

An overload protector during normal and
overcurrent/over heating conditions as
shown in Figure 2.

When there is a high rise in temperature, Figure 2. Normal condition (contact close)
copper expands more than steel, causing
warping (or bending) of the bimetal disc Figure 3. Over control/overheating
which opens the overload contacts thus, (contacts open)
removing the motor from the circuit. When
the temperature goes down to normal Overload protector on normal and overheating or
level, the bimetal disc returns to its normal overheating position.
position and the contact points close.
Figure 4. Parts of an overload protector.
Basic Parts of an Overload Protector

1. Heater - safeguards the
compressor against the overcurrent.
It is in series with the contacts and
the motor windings (see Figures 2
and 3). When the motor is subjected
to a sustained overcurrent, the
current through the heater is high,
and the temperature of the heater
increases. This heats the bimetal
disc.

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2. Bimetal disc and contacts Figure 5. Overload Protection

Safeguards the compressor motor
against overheating. The bimetal is
positioned beside the heater and this
senses the temperature change in the
heater and compressor dome (or
housing). It opens or closes the
contacts depending on the
temperature condition of the motor.

3. Terminals and pin connector

- enable the overload protector to be
electrically connected to the circuit.

4. Case - holds the other parts in place.
Also makes the installation of the
overload protector possible.

B. Internal Overload Protector

Internal overload protector is mainly used
in hermetic motors. It is installed inside the
motor winding and protects the motor from
overheating. When the winding
temperature rises above safe limits, the
internal overload protector opens and
disconnects the motor windings from the
power source, preventing damage to the
motor.

Figure 6. Locations of internal overload protector

Figure 7. Internal overload protector

The contact points are made of fine silver for excellent conduction of current. The bimetal
strip (disc) responds to temperature in the motor windings and closes the circuit when the
temperature goes down to a safe value.

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SELF-CHECK #6

A. Without looking back on the previous pages, answer the following questions on a piece of
paper:

1. What are the functions of an overload protector?

2. How does a bimetal disc open or close the circuit?

3. What is the purpose of the heater?

4. Differentiate an external overload protector from an internal overload protector

B. Below are the parts and an illustration of a overload protector. Identify the parts by writing
the corresponding number of each part in the circle provided in the illustration. When you
have completed the activity. CALL YOUR INSTRUCTOR.

Parts of an Overload Protector

_______________ Case _______________ Bimetal disc
_______________ Terminals _______________ Contact
_______________ Pin Connector _______________ Heater

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INFORMATION SHEET #6

CHARACTERISTICS OF HERMETIC COMPRESSOR MOTOR WINDINGS

OBJECTIVE:

After completing this Information Sheet, you should be able to:

- discuss the characteristics of hermetic compressor motor windings.

SUPPORT MATERIALS:

This Learning Element may be supplemented with the following:

1. Charts about hermetic motor
2. Transparencies
3. Trainers or cut-out view of a hermetic compressor motor

TECHNICAL INFORMATION

Hermetic compressor motor employs two kinds of windings: the starting and running
windings. Figure 1 shows the position of windings in the stator of the motor. They are
positioned this way so that the magnetic force created by each winding complements each
other to create a higher torque or force.

Figure 1. The rotor and stator of hermetic motor.
The section shows the position of the start and run windings.

The start winding is used only during the starting period, that is, when the running winding
alone cannot develop the needed torque (force) to start the compressor. A relay is used to
remove the start winding from the circuit when the motor reaches its full speed.

The windings are insulated from the stator and compressor dome as shown in Figure 1. A
low resistance across the compressor dome or body, and any of the terminals reveals grounded
windings.

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The start winding has a smaller diameter wire and so it has a higher resistance compared
to the run winding. The run winding which is energized every time the compressor runs is made
of heavy-duty wire of bigger diameter.

The table below shows the resistance of the winding, (see also Figure 2).

TERMINALS WINDINGS REMARKS

C&R START Lowest resistance
C&S RUN Medium resistance

S&R RUN & START Highest resistance

COMBINED

Figure 2. Diagram of Compressor
Motor Windings

The sum of the resistances of the run
and start winding is the resistance across S
and R terminals. If the total or the individual
resistances of the run winding (C& R) and
start winding (C & S) is not equal to the S
and R reading. The windings are partially
shorted. If this happens, the compressor
should be replaced with a new one.

To cool the windings during operation, the Figure 3. Refrigerant vapor from the suction line
cool refrigerant vapor from the suction line cools the windings. The oil distributes heat to all parts
flows over, the motor windings. The
compressor oil also helps in the distribution and lubricates the moving parts of the entire
of heat to the different parts of the compressor.
compressor. Figure 3 illustrates these in
details.

At the start, the flow of current is very high, about two to four times than the running current.
This Initial high current is called “locked rotor amperage”. When the motor attains about 75% of

its rated speed, the start winding is removed automatically from the circuit. The run winding

alone drives the compressor. The current passing through the running winding is called the
“running current”.

NOTE: The compressor motor should not be allowed to operate at high current for more than
ten seconds. The windings will be burned and destroyed permanently.

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SELF-CHECK #7

Without looking back at the previous page, answer the following questions briefly in a
separate answer sheet.
1. Which has the highest resistance, the run or the start winding?
2. How high is the starting current compared to the running current of a compressor motor?

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INFORMATION SHEET #7

ELECTRICAL CONTROL, CURRENT AND POTENTIAL RELAYS

OBJECTIVE: After completing this Information Sheet, you should be able to:

- identify an electric control and its function;
- identify a temperature control and its functions;
- describe the construction of current relays and magnetic switches and their

operations; and
- describe the construction and operation of potential relay, by answering the questions

in the Progress Check correctly.

EQUIPMENT, MATERIALS, AND AIDS YOU WILL NEED

QUANTITY UNIT DESCRIPTION
1 pc.
1 pc. Current relay
1 pc.
Potential relay
1 pc.
Schematic diagram of temperature
control switch

Wiring diagram illustrating motor
control

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INTRODUCTION:

An electric control is a device that makes or breaks electrical circuits. It controls the flow of
refrigerant, changes the capacity of the compressor, provides automatic defrosting, and
transfers liquid from one portion of the system to another.

An electrical household refrigerator uses an overload safety control and a motor starting relay,
aside from other electric controls previously described.

The temperature control is used to automatically
start and stop the motor and compressor as
often as necessary to maintain the desired
temperature in the refrigerator.

HOW TEMPERATURE CONTROL OPERATES

1. A thermostatic bulb changed with volatile
liquid, as shown, helps in the detection of
any change in temperature.

2. This change in temperature is transmitted to
the bellows through the capillary tube, as
shown.

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3. The gas pressure on the bellow causes the
bi-metal to expand or contract, as the case
may be, as shown.

4. This expansion or contraction causes the
bimetal to press against the spring, as
shown.

5. The compression of springs causes the
contact point to close and start the motor
and compressor, as shown.

6. As the motor runs, the control bulb is cooled
and the pressure in the bellows is reduced.
The reduction of pressure allows the spring
to push the bimetal in opposite directions,
snapping the switch and stopping the motor.
The control bulb slowly warms up until the
motor starts again and the cycle is repeated.

Current relays and magnetic switches are
generally used on low torque smaller (H.P.)
motors. Shown below is the diagram of a
current relay switch.

Relay – current type

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Shown below is a diagram of current relay and magnetic switch connection.

Current Relay Connection

CURRENT RELAY AND MAGNETIC SWITCH OPERATION

1. Current relay and magnetic switch are
normally open, as shown.

2. This normally open contact closes
immediately when the motor is energized
by the surge of current which occurs at the
time of starting (see illustration at right).

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3. When the motor speeds up, the current drops and the magnetic coil which is in the main
winding circuit releases the movable contact, disconnecting the starting winding, as shown.

4. POTENTIAL RELAYS are generally used on high torque capacitor motors. Shown below is
diagram of the parts of a potential relay.

Parts of Potential Relay
POTENTIAL RELAY CONNECTIONS
High starting torque motors 2 terminal overload potential relay

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1. The contacts are normally closed, as
shown.

2. The coil is continuously connected to the
starting winding, as shown.

3. The coil opens the starting contact when a
predetermined voltage appears across it,
as shown.

4. The contacts remain open during normal
operation, due to the induced start winding
voltage, as shown.

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5. Contact closes when the voltage across it
is cut or stopped.

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SELF-CHECK #8

Read the items carefully and answer each question correctly. Write only the letters on the space
provided.

_____ 1. The function of which is to disconnects the motor from the source when the motor
becomes overloaded

a. pressure control
b. thermostat
c. temperature control
d. overload protector

_____ 2. Which one is NOT an electric control?

a. float switches
b. relays
c. capacitor
d. thermostat

_____ 3. An automatic switching device that disconnects the starting winding after reaching its
three-fourth rated speed is called

a. relay
b. overload
c. thermostat
d. running capacitor

_____ 4. A relay generally used on low torque smaller H.P. motor.

a. potential
b. current
c. pilot
d. capacitor

_____ 5. A winding of the motor that is disconnected when the motor has reached its
equivalent value

a. running
b. common
c. starting
d. secondary

_____ 6. Current and potential relay has similarities except in

a. overload
b. compressor terminals
c. control
d. motor capacity

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_____ 7. When the motor resumes its normal operation, this winding is the only one connected
to the circuit.

a. starting
b. running
c. secondary
d. common

_____ 8. A type of relay generally used on a high torque capacitor motor.

a. potential
b. current
c. pilot
d. hot wire

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ANSWER KEY to SELF-CHECK #8

1. d
2. c
3. a
4. b
5. c
6. d
7. b
8. a

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INFORMATION SHEET #8

CAPACITORS: TYPES AND FUNCTIONS IN A REFRIGERATING SYSTEM

OBJECTIVES:

After completing this Information Sheet, you should be able to:

- Enumerate and discuss the characteristics of capacitors used in refrigeration and air
conditioning; and

- Explain the functions of capacitors in a circuit.

SUPPORT MATERIALS

For more information, refer to the following support materials:

1. Trainer
2. Charts
3. Transparencies

TECHNICAL INFORMATION

A capacitor is a device used to store electricity. It is usually made of two aluminum foils
separated by insulating materials. Leads are attached to the plates. See Figure 1 for
details.

Figure 1. Capacitor Construction

The basic function of a capacitor is to store electrical energy and release it when needed.
In refrigeration and air conditioning, it is used to help start motors to improve their power
factor.

All capacitors have two basic ratings the microfarad (mfd) rating and the voltage rating.
The microfarad rating identified the capacitor’s electrical storage capacity which is
capacitance, while the voltage rating identifies the maximum voltage that can be applied
across the plates.

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In specifying capacitors, both capacitance and voltage ratings are given.

Capacitors may be connected to a line with a lower voltage but not to a line with a higher
voltage. This means that a capacitor with a 220 volt rating may be connected to a 110
volt circuit, but a capacitor with a 110 volt rating cannot be connected to a 220 volt line.

Figure 2A shows the two types of capacitors used in refrigeration and air conditioning,
the starting and the running capacitors. Sometimes, both of these capacitors are
enclosed together in single case (see Figure 2B).

Figure 2A. Starting capacitor Figure 2b. Running capacitor with fan capacitor

Starting Capacitor

Starting capacitors are intended for short and Figure 3. Wiring diagram for start and run capacitor
infrequent compressor starts (see Figure 2A).
They are made of aluminum foil, paper and a
material in paste or liquid form called
electrolyte. The starting capacitor is connected
in series with the starting winding as shown in
Figure 3.

The starting capacitor is intended to give additional power to the motor during the starting
period. Because this power is not necessary after the motor has attained its normal operating
speed, the current is automatically cut off from the starting winding by the starting relay to which
the starting capacitor is connected in series.

Running Capacitor

This is a heavy duty type-oil filled capacitor. it is lower in microfarad rating than the starting
capacitor. (See Figure 2B). It remains in the circuit at all times during compressor operations,
(see Figure 3). It is constructed in such a way that heat does not build up excessively.

The running capacitor also increases the rotating force during the starting period and
improves the motor’s running efficiency. It also reduces the running amperage (current) by
increasing the power factor of the motor.

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SELF-CHECK #9

Without looking back at the previous pages, answer the following questions briefly:
1. Explain the function of a starting capacitor.
2. Differentiate a starting capacitor from a running capacitor.
3. How are capacitors specified?

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INFORMATION SHEET #9
THE THERMOSTAT

OBJECTIVES:

After completing this Information Sheet, you should be able to:

- state the function and operating principle of the thermostat;

- state the purpose of the range and differential adjustment;
- install the thermostat according to a diagram satisfying the instructor’s checklist in the

Progress Check; and

- describe the methods of adjusting the range and differential setting; and answer all
the items in the Self-Check correctly.

EQUIPMENT, MATERIALS, AND AIDS YOU WILL NEED

QUANTITY UNIT DESCRIPTION
1 piece Screwdriver
1 piece Thermostat
Sample of a thermostat
Illustration of a thermostat

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INTRODUCTION
Most refrigerator manufacturers design their units to operate only for 8 to 14 hours a day. This
is done by means of a thermostat temperature actuated control.
FOUR TYPES OF SENSING ELEMENTS OR BULBS USED IN A THERMOSTAT
1. Sensing element with gas charged

temperature bellows.
2. Vapor pressure temperature bellows.

3. Liquid charged temperature response
diaphragm.

4. Capillary tube coil used as bulb.

5. The capillary tube is the one that contacts the sensing element and the operating
mechanism.

6. Copper has a greater coefficient of expansion than iron. This bimetal strip will bend as the
temperature changes. The bending action of the bimetal will open and close the contact
point in an electrical circuit. You will observe that when the bimetal is heated, it bends
upward and when cooled, it bends downward.

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FUNCTIONS OF A THERMOSTAT
1. It starts the compressor driving motor.

2. It stops the compressor driving motor.

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