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A. O. SmithLevel 2 A. O. SmithLevel 2
Introduction
This application guide is not intended to be a
repair manual for any of the equipment
described. It is intended to provide general
knowledge to persons working in fields related to
electric motors and to provide service information
to qualified persons.
Motors are of little use by themselves. They
are designed to be coupled to some other part and
convert electrical energy into mechanical energy.
The selection of a replacement motor for a specific application would be a very involved process
if it were necessary to start with the basics of
magnetism, electricity, and motor construction
each time a replacement was required. In order
to present replacement motor offerings in a logical, orderly manner, the motors are grouped by
type, construction, and often, the application for
which they are intended.
Motors in original applications are designed to
be operated under specific conditions. If the
equipment or installation is modified, the motor
may be overloaded. For example, if a furnace
designed for use in a home with duct work is
placed in a shop and has little or no supply duct
work, it may be close to a free blow condition (no
static pressure or resistance to air flow). The
motor may become overloaded.
A.O. Smith’s replacement motor selections are
identified by applications where possible. This
makes it easier to narrow the choices in the
selection process.
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 1
32 Motor Troubleshooting Guide
� Most motor applications have service manu-
als whose procedures, especially those involving safety, should be followed. Within the
scope of this discussion, the assumption must
be made that the procedures have been followed to the point where the motor is suspected, and proper voltage (nameplate as connected
+
10%) is available to the motor.
� In addition to the electrical hazard, an
applied motor could be very hot if a start was
attempted during other test procedures.
� Always ground motor and secure so starting
torque will not cause it to move in bench test.
� Always use the proper tools (not a hammer)
to remove fans and pulleys from a motor that
is to be reinstalled. Likewise, never pound
anything onto a motor shaft. A ball bearing
can easily become brinelled or work hardened
leading to eventual failure.
� In a new installation of new equipment that
does not start, follow the established procedures to the point where a motor check is recommended. The procedure is basically the
same for a replacement motor on an existing
application except the case where the motor
burned out as soon as the power was applied.
In this case, the motor was probably hooked
up wrong.
� On a replacement motor there is slight possi-
bility that the wrong nameplate was applied.
Does the connection information physically
match the motor? Are other motors with the
same part number but different date codes
the same? Specific resistance values from the
manufacturer may be required for positive
confirmation.
A. O. SmithLevel 2
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2 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
HEATING, VENTILATING, AIR CONDITIONING &
REFRIGERATION (HVAC&R)
Heating and air conditioning applications often
use the same types of motors or share the same
motors if the systems are combined. Heating systems using motors heat either air or water. Once
heated, the air or water is moved by a motor and
blower or motor and pump.
All air conditioning systems using motors within the scope of this manual use essentially the
same principles. The components may look different depending on the system capacity and
configuration.
Heating,
Ventilating,
Air Conditioning &
Refrigeration
(HVAC&R)
Motor Troubleshooting Guide 31
� If motor appears to run okay it may be okay.
Or, it may have an internal problem such as
loose or plugged cooling fan. It is possible for
a winding coil to be shorted onto itself without indicating an open condition. The motor
would be weak and probably overheat under
load. If the motor has a terminal board, connections could be loose causing intermittent
operation.
� Check for phase imbalance on three phase
systems.
� Checking a motor in its application is the
only practical method for most people to
determine performance under load. If the
motor is defective, the application provides
many clues to help determine the cause . Did
the motor fail due to a defect or old age. Or,
was its failure hastened by the application or
environment? The application is the only
place an attempt may be made to check voltage.
� On permanently installed equipment, the
voltage may vary depending upon the total
system load. It can also vary with the total
load on the power company grid.
� Mobile equipment such as rental units are
often abused through the use of inadequate
extension cords or undersized generators.
� Was the motor misapplied or has the applica-
tion load change? Dirty or blocked coils may
overload a condenser motor. Reduced static
pressure may overload a motor driving a
blower wheel.
� Is the belt driven load free to turn, and in
proper operating condition?
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A. O. SmithLevel 2 A. O. SmithLevel 2
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 3
THE REFRIGERATION CYCLE
The refrigeration cycle involves a number of
physics principles to convert energy from one
form to another, and to transfer that energy from
one point to another.
One of the principles in the change of state.
Just as it takes energy to change ice at 32
degrees fahrenheit to water at the same temperature, energy transfer is required to change the
state of a refrigerant.
The diagram below describes the refrigeration
cycle. Simply stated, electrical energy in the case
of an electrically driven compressor, compresses
the refrigerant gas and causes it to move through
the system where it changes from a gas to a liquid and back. In addition to the changes in gas
volume, heat is added or taken away at different
points in the process.
The
Refrigeration
Cycle
▼
▼
▼
▼
▼
▼
▼
DISCHARGE LINE
SUCTION LINE
LIQUID LINE
RECEIVER
EXPANSION
VALVE
CAPILLARY TUBE
BLOWER/MOTOR
BULB
FAN/MOTOR
COMPRESSOR
EVAPORATOR
CONDENSER
HIGH PRESSURE SIDE
LOW PRESSURE SIDE
REFRIGERATION DIAGRAM
30 Motor Troubleshooting Guide
� On belt driven loads with sleeve bearing
motors, check to see that the motor is oriented properly in relation to the bearing’s oil
wick window.
� Excess heat is the enemy of a motor. If the
motor has been operating properly, has anything changed? Is the voltage too high or too
low? Is the ambient too high for the motor?
Are internal or external fans clean and
intact? Has foreign material gotten into the
motor? Is normal air f low around the motor
blocked, causing recirculation?
� Is there any evidence of physical damage or
overheating?
� In applications such as direct drive furnace
blowers, the motor needs system air for cooling. There is not a general rule of thumb,
but use of a replacement motor significantly
stronger than the original may result in overheating. Speed will be up and the system
may not provide enough air for cooling.
Select a close replacement and check amps
after installation.
� Check windings for continuity.
� Check for continuity between motor leads or
terminal board and frame as indication of
short to ground.
� Check capacitor if capacitor start and/or run.
� Check the overload if accessible.
� If a single phase motor with a mechanical
start switch starts but does not come up to
speed, check the switch for proper operation.
If this same type motor just hums and does
not start, check the switch and start winding.
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4 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
Electrical energy is converted to mechanical
energy by the compressor motor. The compressor
draws a refrigerant gas from the evaporator, compresses it and sends it to the condenser where it
is liquefied. Refrigerant gas entering the condenser is full of heat picked up from the previous
cycle plus heat from the compression cycle. In
the condenser, heat is removed from the refrigerant and it returns to the liquid state. An expansion valve controls the flow of refrigerant
between the condenser and evaporator. The temperature of the gas entering the evaporator is
lower than that of the air to be cooled. Heat is
removed from the air to be cooled. This heat is
absorbed into the liquid refrigerant causing a
change of state back to a vapor. The cycle continues until a thermostat senses that the desired
temperature has been reached and shuts the system down.
HERMETIC COMPRESSORS
The motors and other components of the system operate in a closed system and must be compatible with each other. Compressors are designated as hermetic or semi or accessible hermetic
depending on the type of construction. The word
hermetic means an airtight seal or sealed from
outside elements. Typically, home refrigerator,
room air conditioner, home air conditioner, and
small commercially applied compressors are in a
welded shell, leading to the hermetic designation.
Larger commercial compressors use castings and
other parts, similar to an automobile engine,
which are bolted together and get the designation
accessible hermetic.
Hermetic
Compressors
Hermetic Stator/Rotor
Motor Troubleshooting Guide 29
Knowing why a motor failed may be important
in selecting the proper replacement motor, and
insuring a good service life.
Try to determine the age of the installation and
if the motor is the original. If the motor is a
replacement, how long has it been in service?
Does it appear to have been properly installed?
What is the duty cycle or service period?
Having some indication of the problem often
indicates items to check first. A bench check is
usually a confirmation of a suspected problem.
The type of motor and its construction will
dictate which items may be checked without
disassembly.
The following tips and suggestions are by no
means complete, but offer some of the basics
relating to a motor and its application. Other
modules cover some subjects in more detail, and
specific knowledge from other sources may be
needed.
� To the degree possible, check the same areas
in the application as would be done in a
bench test.
� Is there any evidence of water damage?
� Does the shaft turn freely?
� On sleeve bearing motors, check end play
(.01-.06” normal). Lack of end play could
cause motor to bind when hot.
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A. O. SmithLevel 2 A. O. SmithLevel 2
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 5
The function of both types is essentially the
same. Due to the initial cost of the larger systems, parts may be salvaged and used in rebuild
or remanufacturer operations.
Hermetic motors are used in hermetic compressors. The sealed system contains a refrigerant
gas and lubricating oil.
Hermetic motors are functionally the same as
other types of motors except that the housing,
bearings and shaft are provided by the compressor manufacturer. These motors are often
referred to as rotor/stator kits. Single phase versions are often of the permanent split capacitor
(PSC) type which does not require a starting
switch. Systems using PSC compressor motors
often have “Dual Can” capacitors which are two
separate capacitors in one housing. One capacitor is used for the compressor and one for the fan
motor.
A.O. Smith has a selection of hermetic
rotor/stator kits for rebuild and remanufacture
operations.
28 Motor Troubleshooting Guide
Motor
Troubleshooting
Guide
Some procedures require special tools and specific product knowledge which is beyond the
scope of this module.
These tips and suggestions are offered for persons with proper qualifications and necessary
test equipment, and as information of general
interest to persons in the replacement motor
distribution channel.
There is not a single listing of motor troubleshooting procedures to be followed in a given
order. The procedures will also differ for new
and existing installations and motors that are
being bench checked. As with anything dealing
with electricity, personal safety is the prime concern.
BENCH CHECK
First, consider what symptom lead to the
motor’s removal from service. Examples: “It was
noisy,” “it wouldn’t start when the power was
applied,” “it tripped the breaker,” “it runs for several minutes then shuts off,” “it just hums when
power is applied,” “smoke came out when it was
turned on.”
WARNING!
This is not a guide for
the do-it-yourselfer.
Bench Check
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6 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
HVAC&R
Application
Basics
HVAC&R APPLICATION BASICS
Many motors for heating, ventilation, air conditioning and refrigeration applications are
designed special purpose. Knowing the application makes it possible to begin the selection
process at a point where the possible replacement
will likely be found. An understanding of the
application will help assure that the best possible
selection is made.
A heat pump performs the same functions as an
air conditioning system, but contains a valve
which changes the refrigerant flow and in effect
changes the evaporator into the condenser and
vice versa. In heat pumps the coils are commonly
called the indoor and outdoor sections. In the heat
pump mode, heat is removed from the indoor coil
and added to indoor air, and heat is added in the
outdoor coil. Heat is present in all substances
including air and water until absolute zero is
reached at which point all molecular activity stops.
As an example, air at 30 degrees fahrenheit may
seem cold but it is warmer than air at 20 degrees
fahrenheit because it contains heat.
Because they incorporate a change of state of
the refrigerant, it is possible for heat pumps to be
more efficient than straight resistance heat. This
efficiency is expressed as a measure of watts
input to BTU output. A heat pump’s efficiency
decreases as the outside temperature decreases.
Electric resistance strip heat is often incorporated into heat pump systems and is activated when
the heat pump cannot meet the demand for heat.
Some systems use water instead of air as the
heat transfer medium in the outdoor section.
The water may be a constant source in a drilled
well or a f lowing source. Heat pumps are also
used to transfer heat to swimming pools.
In systems using air as the heat transfer medium, fans driven by electric motors are used to
move air over the evaporator and condenser coils,
facilitating heat transfer. Propeller fans are the
norm on the outside sections with blower wheels
used indoors.
Special Purpose Motors 27
EXPLOSION PROOF APPLICATIONS
Motors used in hazardous environments such
as flour mills and gas pumping applications
require special construction features so that a
short or spark in the motor will not ignite flammable liquids, vapors or dust that may be present. The design, manufacturing and application
of these motors is subject to Underwriter’s
Laboratory rules and many other local and
national codes.
Many OEM gasoline pump motors have special
mounting flanges and on/off switches and are not
replaceable by stock type motors.
Due to the liability potential, recommendations
should not be made as to the application of these
motors. The person making the purchase should
have the training and qualifications to know the
exact motor required.
POULTRY DUTY FAN MOTORS
Commercial poultry house fans use both aluminum and steel propeller blades, direct or belt
driven, mainly by base mounted motors. The
designs are usually totally enclosed, air over
(TEAO), meaning they rely on the blade’s air
movement for cooling air.
It is essential to the chicken’s survival that hot,
stale air is exhausted.
TRANSFORMER COOLING FAN MOTORS
These are very specialized direct drive propeller fan motors used to cool large electric utility
transformers. They are sometimes referred to as
“fin fan” motors. The design is very robust,
employing ball bearings and stainless steel
shafts. Replacement motors are normally
secured through the original equipment channel.
Explosion
Proof
Applications
Poultry Duty
Fan Motors
Transformer
Cooling Fan
Motors
XP1070
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A. O. SmithLevel 2 A. O. SmithLevel 2
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 7
Outdoor
Section—
Residential
OUTDOOR SECTIONS—RESIDENTIAL
Enclosed motors are widely used in new outdoor installations. The use of enclosed replacement motors has risen dramatically in recent
years. The service person may use one motor for
both enclosed and open applications, reducing
inventory dollars. Even though a motor is totally
enclosed, it still needs to breathe and have a
place for moisture to drain. Replacement motors
typically have drain holes in both end frames. A
plug is required in the hole on the top of the
motor as installed. If a motor has two plugs, the
one on the bottom should be removed. If only one
plug is provided, it should be installed in the top
hole.
If it is possible for rain or other moisture to
accumulate on the motor leads, the leads should
be placed to form a drip loop so the moisture will
not drain into the motor’s other components.
Almost all units being built today have 60
degrees celsius (140 degrees fahrenheit) fan
motors on the hot side of the coil. The ambient
or outside air is pulled through the coil, picking
up additional heat before it passes over the
motor. If the ambient air is first drawn over the
motor and then pushed through the coil, the
motor has a lower operating temperature.
If a motor rated 40 degrees celsius (104 degrees
fahrenheit) is installed on the hot side of the coil,
nuisance tripping may occur, especially in high
ambient situations.
Motors used on residential systems are usually
sleeve bearing. Light commercial units which
look just like the residential units may have ball
bearing outdoor motors. The motor should definitely be a special ball bearing design if a speed
control device is used.
FSE1036
Totally Enclosed Outdoor
Sleeve Bearing Fan Motor
FE1036
Totally Enclosed Outdoor Ball
Bearing Fan Motor
26 Special Purpose Motors
Some electric compressor horsepower ratings
have been determined by comparing the CFM to
a compressor using a gasoline engine. Since the
gasoline engines are not as efficient as electric
motors, a compressor may be called five horsepower even though the motor does not actually
develop five horsepower. Amps are important in
the final motor selection since they determine the
required circuit capacity to which the compressor
will be connected. A replacement motor with the
equivalent horsepower and service factor may not
be acceptable due to the efficiency of the original
motor. Some motors are capacitor start and run,
with more than one run capacitor. A replacement
capacitor start only motor may have running
amps which are too high.
CARBONATOR PUMP
These motors are used in beverage dispensing
systems. The shaft extension is special and
designed to mate to the pump. Carbonator pump
motors are also used in hydraulic pump applications. Even though the mounting is special, it is
uniform among motor manufacturers.
SUMP PUMP
Motors used on sump pumps may be of the
pedestal type and mounted on the end of a support column (1-1/2”ID or 1-3/4”OD), or the
immersible type. Most smaller immersible types
are not repairable. Key factors in selecting a
pedestal type replacement are horsepower, service factor, enclosure, protector/overload and hub
dimensions.
SEWAGE/EFFLUENT PUMPS
Motors used in these applications are sealed in
a housing and may or may not be repaired or
replaced by a qualified service person. The electrical designs are generally similar to stock type
motors, but their mounting is special. The original equipment manufacturer should be contacted
regarding replacement.
Carbonator
Pump
Sump Pump
Sewage/
Effluent
Pumps
CB2024A
SP2030A
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8 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
Motor usage is heavily weighted to six pole
(1075 RPM) designs, followed by eight pole (825
RPM) then four pole (1625-1725 RPM) units.
Two speed motors are used on some units to
reduce operating speeds and costs when lower
ambient temperatures do not require as much air
flow over the coil.
Since the horsepower required for the fan
varies directly as the cube of the speed, a six pole
motor cannot be used to replace an eight pole
motor. Depending upon the static conditions, the
same fan blade may require almost three times
the horsepower to run at 1100 RPM as it does at
825 RPM.
Typical mountings are lug, belly band or
extended motor thru bolts. Some motors use
screws in tapped holes in the main frame to
attach mounting strips or cables.
Blocked coils reduce air flow to cool the motor
and can cause an overload condition.
Fans may be statically balanced, but dynamically out of balance due to bent blades. This condition may lead to bearing failure.
The term split system refers to units with separate indoor and outdoor sections connected by
refrigerant line. Packaged units as the name
implies, have all the components in one place.
Room air conditioners, commercial rooftop units,
PTACS (Packaged Terminal Air Conditioners)
and mobile home packs are examples of packaged
units. Even though packs and commercial units
are entirely outside and only ducted to the inside,
they have a physical barrier between the inside
and outside sections.
FS1037S
Closed Except Lead End
Outdoor Sleeve Bearing
Fan Motor
Lug Mount Adapter Bracket
Special Purpose Motors 25
GARAGE DOOR OPENER MOTORS
COMMERCIAL DOOR OPENER MOTORS
GATE MOTORS
In general, these motors are excellent examples of good design and application and provide
testimony to the reliability of today’s motor production processes. If a motor does have a
defect that will lead to failure, that failure is
most likely to occur early in the warranty period at which time the entire unit is replaced. If
a motor fails at some later time, it is usually
less expensive to replace the entire unit.
Commercial units utilize reversing switches
and are usually serviced by door firms who get
their motors from the original equipment manufacturers.
AIR COMPRESSORS
Motors used in air compressor applications
may be belt drive or direct drive. On direct
drive units, the compressor housing usually
provides support for the shaft extension end
bearing. As such, these are partial motors and
replacements are not available in a stock motor
line. Belt drive compressors use a more conventional motor with a base and single shaft
extension. Horsepower, service factor and
RPMs are the keys to identifying a replacement
motor. The horsepower and CFM (cubic feet
per minute of air) characteristics of compressors are often advertised. Commercial/industrial compressors use NEMA frame motors with
identifiable service factors. Hobby compressors
often have motors with the service factor
marked as special. Special means less than
one.
Also, keep in mind that there is a range of
performance within the same horsepower rating, depending upon motor type and manufacturer. Check the replacement motor amps after
installation to verify selection.
Air
Compressors
Garage
Door Opener
Motors/
Commercial
Door Opener
Motors/
Gate Motors
CP1502M
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Heating, Ventilating, Air Conditioning, & Refrigeration Motors 9
Commercial systems whose components and
configurations differ from basic home and commercial packaged and split systems may also use
fractional horsepower motors in either indoor or
outdoor sections. Fan coil units with a motor and
blower wheel(s) are used in systems where
chilled/heated water or refrigerant is piped
through a building instead of using a central
blower and duct work. Some chillers use the
same type outdoor fans and motors as rooftop
and packaged units.
Motors used in commercial applications such as
condensers usually have ball bearing construction because the loads are heavier. Sleeve bearing motors typically are quieter than ball bearing
motors and are favored in indoor air moving
applications.
Ball bearing motors may be used to replace
sleeve bearing motors but not vice versa unless
you are certain they will meet all application
requirements.
FC1106
“Patented” Fan Canopy
Deluxe Commercial
Condenser Fan Motor
FY3106
56 Frame, 3Ø Totally Enclosed
Ball Bearing Commercial
Condenser Fan Motor
FB3056
Base Mounted, 3Ø
Outdoor Ball Bearing
Condenser Fan Motor
BK1072
Commercial Indoor
Blower Motor
24 Special Purpose Motors
Special Purpose
Motors
Following are some examples of special purpose
motor applications. Keep in mind that the original equipment was tested to insure that the
motor would operate safely and properly under
the conditions for which it was designed.
Modification or misapplication may be unsafe
and detrimental to the motor or equipment.
There are literally thousands of applications
using general purpose type motors with mechanical and electrical variations. Each of these variations must be evaluated to determine if a stock
motor will work, possibly with modifications, or if
a replacement must be obtained from the OEM.
GLASS WASHERS
Sump pump motors are often used on glass
washers used in bars. This use is not condoned
by motor manufacturers. A motor designated for
glass washer duty should be used and wiring
must be done in accordance with all applicable
codes and include a ground fault device.
Glass
Washers
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10 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
FURNACES
Furnaces generally use motors for three functions: move either heated or cooled air, move
fuel, and provide air for combustion. A specific
furnace may use more than one motor. High efficiency furnaces capture more of the heat of combustion and use a motor and blower to provide
combustion air and exhaust flue gases. These
motors are commonly called draft inducer motors.
“C” frame and 3.3” are the most common motors
used in this application.
Natural gas and propane f low through control
valves into the burner area of a furnace under
pressure. Oil furnaces use a motor and pump to
spray the oil into the burner area. NEMA standard M and N flange motors are common in oil
burner applications. Rotation, horsepower and
flange type are key elements in motor replacement.
A furnace burns substances such as natural
gas, oil, propane, wood and coal. The heat
exchanger separates the combustion process from
the air in the space being heated. The motor and
blower circulate air through the heat exchange in
a continuous cycle until the desired temperature
is reached. In most cases, a thermostat and control circuit is used to operate the cycle.
The thermostat controls the combustion cycle.
The control circuit senses the plenum temperature within the furnace and signals the blower
motor to start and stop. This same control circuit
also shuts off the combustion process if the blower motor fails to start.
Furnaces are designed as hi-boy or up-f low,
counterflow or downflow, low-boy and horizontal,
depending upon the space in which they are
applied. The motor/blower performs the same
basic function in all designs.
Furnaces
EL2002
Reversible Switch Model Oil
Burner Motor
General Purpose Motors 23
General Purpose Motors
General purpose motors as their designation indicates
may be used in a variety of applications. The designer of a
piece of equipment can tailor the load so that a general
purpose motor may be applied. The system consisting of
the motor and the driven load often has a rating which
indicates the standard and maximum amount of work it
can do. The ratings may or may not include an overload or
safety factor. As an example, a hydraulic pump system
used to power a lift has a limit to the amount of pressure it
can develop and transfer to other system components. If
the lift is rated for 10,000 pounds, and the load is 20,000
pounds, a relief valve must open or the weakest link in the
system will fail. The replacement motor should be equivalent to the original design. A weaker motor would not allow
the system to operate as designed. And, a stronger motor
may create an unsafe condition. In the case of a table saw,
the load varies depending upon the type of wood being cut,
and the speed of the cut. A 1/2 horsepower motor may be
suitable to start and run the saw and cut pine, but it may
be okay to apply a 1-1/2 horsepower motor to the same saw
in order to cut oak.
The important point here is to select a replacement
motor equivalent to the original unless you have enough
knowledge of the application to be certain that a stronger,
weaker or different type of replacement motor is acceptable
and safe.
POWER TOOLS
General Purpose NEMA 48 and 56 frame, 2 pole and 4
pole motors are common on contractor and home type tools
such as drill presses, jointer planners and table saws.
Motors should have manual overloads or no overload.
There are no exceptions to this rule - EVER! If a motor had
an automatic overload and tripped, it could start unexpectedly after cooling and cause injury.
The information and procedures described in the replacement module of this series will assist in determining that
you are dealing with a general purpose motor. Catalog listings of general purpose motors are organized by physical
and electrical characteristics to aid in the selection process.
Power
Tools
EB3104
3Ø Enclosed
Industrial Duty
RB1074
Capacitor Start
Resilient Base
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Heating, Ventilating, Air Conditioning, & Refrigeration Motors 11
A squirrel cage blower wheel powered by a
direct drive PSC motor is the most common system now used in residential systems because they
are efficient and compact. Six pole (1075 RPM)
multi speed motors are now the norm. Some
eight pole (825 RPM) motors are also used. Belt
driven blowers were common in the past and
many are still in use. Four pole (1725 RPM)
motors are the most common. Some two speed
motors are used in conjunction with electronic air
cleaners to provide continuous air movement to
reduce drafts. Two speed belt driven motors may
have one of two different types of internal switches. One type requires an external relay to switch
from high to low and low to high speeds.
As mentioned above, three speed, direct drive,
permanent split capacitor, 1075 RPM motors are
the most common. The speeds are available so
that the air flow may be tailored to the installation. Different speeds are needed to move the air
depending upon the static pressure in a system.
High speed may be used if the system has air
conditioning since more work is required to move
the cold air which is heavier. Medium speed
could be used to move air in the heating mode.
The wire lead from any speed(s) not being used
should be insulated separately and secured so
that it does not cause a short.
Furnace blower motors are available in both
115 and 230 volt versions. The 115 volt versions
are a throwback to the days when most homes
did not have 230 volt systems. 230 volt versions
are more common today, especially on electric
furnaces.
FDL1036
High Efficiency Indoor
Blower Motor
GF2034
Belt Drive Blower Motor
22 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
The propeller fan moves air by the wedge
action of the blades. If the blades are cupped, air
will move away from the cupped side. If the
blades are f lat (normally they are not) as in
Diagram C, air will move in either direction
depending upon motor rotation.
The lower edge of the fan blade, as related to
the wedge action, is the leading edge just as the
thinnest part of a wedge goes in first to split a
log.
Blower wheels are centrifugal fans. As with
any centrifugal action, the speed is greatest at
the outermost portion of the device, in this case,
the wheel’s outside diameter. The fins may be
slanted in the direction of the air flow, but this is
not always the case. If the motor and wheel are
not together, it will be necessary to determine on
which side the motor mounts.
If the motor applied to the blower wheel in
Diagram B ran in the opposite direction, air
would move in the same direction as shown but
not efficiently.
Replacement motors often have rotation letters
such as CWLE (clockwise, looking at the lead
end) or CCWLE. The letters CWPE (clockwise,
looking at the pulley or shaft extension end) are
also used on some motors.
Drawing a simple sketch of the motor, fan and
unit often helps in the orientation process.
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12 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
Electric furnaces are a combination of wire
strips and an air handler. The resistance of electricity flowing through the wire strips creates
heat. The strips heat air which is circulated by
the air handler. Electric furnaces use the same
type of air handlers and motors as other types of
furnaces.
Some furnaces use variable speed motors run
continuously. This feature prevents air from
becoming stratified and drafts are reduced. Also,
with an electronic air cleaner, the air is constantly being circulated.
Furnace motors are normally of an open construction since they are in a relatively clean, dry
and protected environment.
Multi speed direct drive blower motors are normally designed to have at least 100 RPM difference between speeds. It is not possible to know
exactly where a given motor will operate on one
of the lower speeds unless a loading point is
determined. Multiple horsepower ratings and
speeds shown on stock motors are offered as a
guide and are not exact. It is not possible to
determine speed on a bench with a strobe since
the motor is not loaded and will operate close to
the same speed on all taps. These motors may
trip the overload on a bench test since they are
not loaded and will run faster than in an application, and do not have the necessary cooling air
being drawn over them.
Most HVAC&R direct drive motors have nonNEMA standard mountings and shafts and have
frame suffixes of “Y” or “Z”. This does not mean
that stock replacements are not readily available.
In many cases, stock motor shafts will need to
be shortened for specific applications. Care must
be taken to avoid bearing damage.
DL1036
Standard Efficiency Indoor
Blower Motor
FM1036
Fleximount Indoor
Blower Motor
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 21
Rotation
Rotation on some double shaft motors may
effectively be changed by rotating the motor
180˚. The rotation of any three phase motor is
reversed by switching any two of the three line
leads.
There are several ways to identify the rotation
of a motor in the application.
1. Look at the motor nameplate, connection
diagram and physical connection.
2. If the motor has not failed completely and is
still operable, observe the rotation and mark
the end frame or main frame.
3. Look for a rotation arrow on a propeller fan
and blower wheel or housing.
4. Determine which way the air must flow in
the unit and then look at the propeller or
wheel and housing.
Diagram A
Diagram B
LEADING
EDGE
LEADING
EDGE
LEADING
EDGE
AIR OUT
SIDE VIEW
MOTOR
WEDGE
ACTION
FORWARD CURVED BLOWER WHEEL
SIDE VIEW
TOP VIEW
CUPPED SIDE
OF BLADE
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A. O. SmithLevel 2 A. O. SmithLevel 2
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 13
FAN COIL UNITS
These units are a combination of a fan, motor
and coil in one package. While a package containing these components in a residential, cooling
only system could technically be called a “fan
coil”, usually the term refers to commercial and
institutional applications where chilled or hot
water is sent through the coil.
A wide variety of product configurations is
available. The motor and blower wheel principles discussed under the furnace section also
apply here.
One common variety is the classroom type
which uses a double shaft extension motor and
two blower wheels whose length is large compared to the diameter. Using the small diameter
wheels, the desired amount of air may be moved,
but the unit does not protrude too far into the
room. The same type of motor and blower combination is also found in hotel room units which
look like PTACs.
Five inch diameter (42 frame) motors are very
popular, but some 48 frame motors are also used.
Larger commercial direct drive units typically
utilize ball bearing motors.
Fan Coil
Units
DBL6409
1050 RPM, 5 Speed Fan Coil
Motor, 42 Frame
20 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
Fan Blade
and Blower
Wheel Basics
FAN BLADE AND BLOWER WHEEL BASICS
The horsepower needed to drive a propeller fan
or blower wheel varies directly with the cube of
the speed if the static pressure or discharge area
does not change.
The propeller fan needs more horsepower if the
discharge area is reduced (assuming speed does
not change) and the blower wheel needs less.
The reverse of these principles also apply.
The principles above have great importance for
installed motors,and when selecting a replacement motor. As examples:
� Blocked or dirty coils on an outdoor unit
reduce air f low and put more load on the fan
motor, possibly causing the thermal overload
to trip.
� If a 1075 RPM motor is used in place of an
825 RPM motor, the loading is too high and
the motor will not operate.
� It may be impossible to determine if a
replacement furnace motor is properly loaded
if the access panel(s) is not in place - static
conditions have changed.
ROTATION
The selection of a replacement motor obviously
requires one that turns in the proper direction for
the application. Many single phase replacement
motors are dual rotation. Some product groups
have motors that are identical except for rotation
and other groups or specific motors have the rotation which matches the original OEM offering.
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14 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
ROOM AIR CONDITIONERS
Like PTACs, room units have all the components in one package. Semi-enclosed motors are
common, but many units use totally enclosed
motors because of the condensate water coming
off the coils. Belly band lug mount kits and
resilient mount length adapters are often used
with replacement motors.
Motors are single voltage and mostly 230V in
units above 9,000 BTU. Some units have a 277
volt rating (sometimes marked 265 volt) which is
a single phase power source from a three phase
system. The largest percentage of motors are six
pole (1075 RPM) permanent split capacitor
designs. Some shaded pole motors will be found
in the lower BTU unit, but their use has been
declining due to low efficiency.
Some 60 cycle units use four pole (1725 RPM)
motors which are designed to operate at a slipped
down speed in the 1300-1425 RPM range. The
unit design requires speeds higher than 1075,
but operation at true four pole speeds is not
required or desirable from a noise standpoint.
These units require a direct OEM replacement.
Be aware that motors rated for both 60 and 50
cycle will have RPMs listed as 1725/1425. The
1425 RPM in this case is at 50 cycle operation, so
this motor is not an acceptable replacement for a
60 cycle motor with the RPMs listed as 1425.
Room Air
Conditioners
Lug Mount Bracket
End Frame Length Adapter
Kit
SA1016
Room Air/PTAC Motor
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 19
Pedestal Fans
YA2020
Yoke Mount
Miscellaneous
PEDESTAL FANS
Pedestal fan motors are used to circulate air
with a propeller type blade mounted directly on
the motor shaft.
Some motors are base mounted, but more common is the yoke mount which is a bracket welded
or bolted to the motor frame. Extended motor
thru bolts for mounting a fan guard are common.
MISCELLANEOUS
Many applications using small (1/8 HP or less)
motors do not have replacement motors available
since the unit cost is low. Examples include ceiling or “paddle” fans and window and box fans.
Other applications such as humidifiers, hood
exhaust fans, bathroom fans, refrigerators, small
room air conditioners and furnace draft inducers
may use 3.3” diameter motors. Four pole shaded
pole and two pole permanent split capacitor
motor with thru bolt mountings are common.
AO1154, 3.3”
AO120, 3.3”
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A. O. SmithLevel 2 A. O. SmithLevel 2
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 15
PTACS
Packaged terminal air conditioning units are
similar in construction to room air conditioners.
All of the components are in one package. They
are common in hotel/motel rooms, small offices
and apartments. Strip electric heat is a common
option. Heat pump versions are available. Many
different manufacturer’s units have the same
dimensions so they may be used interchangeably
in a standard size wall sleeve.
Some PTAC designs use two single shaft
motors (one for the condenser side and one for
the blower wheel). Designs with one double shaft
motor are more common.
Typical blower motors require air over the
motor for cooling. The blower motor used on two
motor PTACs is on the other side of the unit
bulkhead from the blower wheel and does not get
the same air flow as a furnace blower motor. An
exact replacement should be used, or the unit
should be tested at the maximum ambient condition to insure the motor will not overheat.
AIR CURTAINS
Air curtains move a thin, high volume stream
of air from top to bottom in an open doorway to
keep the air on the opposite side from mixing.
Double shaft motors with blower wheels are commonly used.
PTACs
Air Curtains
18 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
OBG2002
Unit Heaters
Hot Water
Circulators
Whole-House
Ventilators
UNIT HEATERS
Unit heaters are the ductless furnaces that
hang from the ceilings of factories, warehouses
and garages. The motor and propeller fan are
usually visible. Enclosed motors are common
due to the often dusty environment.
Motors may be either belt drive or more commonly, direct drive. The direct drive are usually
42 or 48 frame designs using thru bolt/extended
stud or resilient ring mounts. Replacements are
available with and without bases, and PSC types
often have the capacitor mounted on the motor.
HOT WATER CIRCULATORS
Heating systems that have hot water boilers
use a motor driven pump to circulate the water.
These motors have special shaft extensions and
mounting brackets.
WHOLE - HOUSE VENTILATORS
The units normally mount in the ceiling,
pulling air in through open windows and
exhausting it to the attic where it exits through
vents. Many older units used open drip proof
motors, but most new designs have totally
enclosed motors or some type of metal shield to
reduce the fire hazard. Belt drive motors are
generally four pole (1725 RPM), and direct drive
are mostly six pole (1075 RPM).
UH1036
Ball Bearing, Mounted
Capacitor, Unit Heater Motor
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16 Heating, Ventilating, Air Conditioning, & Refrigeration Motors
EVAPORATIVE COOLERS
These units which are also referred to as
swamp coolers are an alternative to air conditioning in areas where the relative humidity is low
enough that the process is effective. They are
common in the desert southwest and high desert
areas such as Salt Lake City and Denver. Dry air
moves over a media pad saturated with water.
The moisture laden air is blown through the area
to be cooled and exhausted through vents or
slightly open windows. As the moisture evaporates inside the space, a cooling effect occurs.
This is the same as the cooling effect on your
skin when water evaporates after stepping out of
the shower.
Most motors used in home units mount in a
resilient base and have the same ring to ring
dimensions. Replacement motors are often sold
without bases since the base doesn’t normally
fail. Single and two speed units are available.
The motors are connected to the blower wheel
with a drive belt. Proper belt tension is 1/2 to 3/4
inch deflection at the center of the belt span.
The motor pulley must be of the type and size
recommended by the cooler manufacturer. If an
adjustable pulley is used, the pulley should be set
by a technician with the necessary electrical test
equipment. The adjustable pulley allows the load
(blower) to run at a speed compatible with the
motor.
Evaporative
Coolers
V2054
Evaporative Cooler Motor
Heating, Ventilating, Air Conditioning, & Refrigeration Motors 17
To set an adjustable pulley:
1. Open pulley to maximum width and
tension belt.
2. Read recommended motor amp rating at
the highest speed.
3. Using an ammeter, measure the amps at
the highest speed.
4. Stop motor, close pulley one-half turn and
retention belt.
5. Repeat step 4 until the amp reading
meets but does not exceed the motor’s
rated amperage.
IMPORTANT:
If the amperage exceeds the
motor’s rating, the motor will
overheat and stop.
CAUTION: The motor will restart automati-
cally after it cools and the overload resets.
NOTE: Cooler installations not using
duct work will require a smaller
diameter pulley than the same
cooler using duct work. The duct
work creates static pressure or
resistance to air flow which
reduces the motor load and amp
draw.
An easy rule to follow is to check the motor
amperage while running on high speed. It
should not exceed the nameplate amps.
Motors with all copper windings or a combination of copper and aluminum windings are available. With advances in connection methods and
winding insulation, there is little difference in
the reliability of either type.
Many motors are sold at retail with the homeowner doing the replacement.
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