HVACR Study Guide -2015 Flashcards
The Evaporator in a refrigeration system
Is the component where refrigerant boils and absorbs heat
The purpose of the compressor is to change
Low pressure, low temp vapor to a high pressure, high temp vapor
A common refrigerant leak detection device is the
Halide torch
Copper plating of compressor parts is
Caused by contaminants in the system
If not properly installed, a hot gas muffler might trap
Oil
Unit ventilators are usually equipped with outside air dampers to
Provide ventilation air during occupancy and comply with most local or state codes
Face and bypass dampers should be adjusted to provide
Tight shut off to reduce the possibility of overcooling or overheating
With belt driven equipment, alignment of the motor driven equipment pulleys
Is accomplished using a string or straight edge
To assist consumer in making an informed choice when purchasing unitary air condition equipment, the efficiency of such units is expressed as Energy Efficiency Ratio(EER or SEER) the units of which are
BTUH/Watt
Firestats located in the airstream of air handling units
Are required in both supply and return air streams
Should be the manual reset type
Should be non adjustable
A sleeve bearing would typically be used in a motor that
Operates with a light load and where noise is a factor
A bearing used on the bottom of a motor where the shaft is positioned vertically is called a
Thrust
To produce electromagnetism, relative motion is required between a magnet field and a
Conductor
Materials which do not allow there electrons to spin out of orbit easily are called
Insulators
A battery is an example of a
Direct Current
“Current flowing through a conductor in one direction for a split second, then in the opposite direction for a split second” would be a good definition of
Alternating Current
If a pressure gauge reads 5 PSIG at sea level elevation, the corresponding absolute pressure is
19.7 PSIA
5psig + 14.7 psia
Solar________ is the amount of solar thermal energy produced divided by the water heating energy demand of the building
Fractional
The portion of the electromagnetic spectrum to which solar collectors respond _____ and near-infrared radiation
Visible Light
During winter, _______
Daylight is shorter and the Northern hemisphere is angled away from the sun
Unless equipped with OSHA or Canadian Standards Association(CSA) approved ground-fault circuit interrupters, portable electric light used in wet and or other conductive locations as, for example drums, tanks and vessels, shall be operated with ____ volts or less
12
Receivers are usually required in systems having
Evaporative condensers
An important feature of a refrigerant receiver, in the case where the liquid line to the evaporator comes out of the top of the receiver, is a
Dip Tube
A pressure regulator is constructed so that a rise in _______steam pressure reduces off the inlet flow of supply steam
Downstream
A vaccum breaker is used to avoid which of the following
Negative gauge pressure
Lock out relays are used in air conditioning systems to
Prevent compressor short cycling
When measuring the winding resistance of a split phase compressor motor, the smallest value will measure between the
The run terminal and the common terminal
Cavitation in a pump pumping hot water
Makes a pump noisy
Is the result of water boiling into the steam
Is the result of insufficient NPSH
The amount of heat removed to lower the temperature of 15 lbs of water from 39 degrees to 48 degrees
135 BTU
Weight X BTU X Temp
15x1 (48-39) degrees
15 x 1 x 9 = 135 BTU
Atmospheric pressure at sea level is
14.7 psi
A dual element fuse has
A thermal cutout and normal fuse link
A single phase motor in which the run capacitor remains connected when the motor runs is called a
Permanent Split Capacitor Motor
The symbol below would be used to indicate a
Temperature actuated
The symbol below would be used to indicate a ______ switch.
Temperature-actuated
A refrigeration system has a hand-operated needle valve for the refrigerant
expansion device. If refrigeration load and suction pressure remain constant, a
decrease in condensing temperature will:
Result in reduced refrigerant flow unless the valve is opened.
Hand Valve
A simple type of expansion device which can provide an orifice of variable
size is a hand-operated valve. These were popular in ice plants that used
ammonia. Their use was acceptable because of various reasons including
the fact that there were always personnel available to adjust the valve,
and plant efficiency was not very critical. The disadvantage of
manually operated valves is their inability to automatically adjust
the flow rate
A full voltage starter has:
One contactor.
Reduced Voltage Starting
An “across-the-line” starter also known as a “full-voltage” starter, means
that when the contactor closes, the motor is immediately connected
directly to the power supply lines, and full voltage is at once impressed on
the motor. This is the least expensive way to start a three-phase motor.
However, this means that the motor will draw locked-rotor current until it
starts turning. Although this is not of any consequence with most motors,
the starting inrush current of large horsepower motors may cause the
power system voltage to dip, resulting in flickering of lights and other
objectionable effects on other electrical devices such as computers or
television apparatus.
The voltage rating of motor controller holding coils is:
Not necessarily the same as the motor supply voltage
An example of this would be in a high-voltage system (460 volts or higher)
where a lower control voltage would be desirable for safety reasons or
because some required control devices (such as thermostats, etc.) may not
be available in higher voltage ratings. Another example would be where
automatic control system is of low-voltage type, such as 24 volts. In such
cases, the holding coils are obtainable in the lower voltage ratings desired.
A lock-out relay should drop out when:
An overload relay opens
A lock-out relay is an electrically-operated control relay applied in such a
way that it can “lockout” a circuit, or cause it to remain de-energized when
once interrupted, as by some malfunction such as the tripping of a safety
device.
In starting up a chilled water system, the first piece of equipment to start should
be the:
Chilled water pump
The chilled-water pump is manually started by pushing the start button.
When the chilled-water pump is running, an auxiliary contact in its starter
completes the circuit. If in the “continuous” position, the condenser-water
pump will run whenever the chilled-water pump runs; if in the “automatic”
position, the condenser-water pump will run on calls for cooling. The
cooling-tower fan can be run at any time for test purposes by putting the
control switch in “manual” position. For normal operation in “automatic”
position, the cooling-tower fan can run on calls for cooling when the
condenser pump is in operation. The interlock is accomplished through an
auxiliary contact in the condenser-water pump starter which, upon closing,
feeds control power to terminals in the machine control panel. The
presence of control voltage at the terminals in the control panel also
permits the lubricating oil pump to start, and when oil pressure has built
up to normal, the compressor can start.
In a gas-fired warm air furnace, the furnace fan should:
Be controlled by furnace bonnet temperature
Bonnet temperature is sensed by the combination fan and limit control. As
the bonnet warms up, the operating control switch will close, and start the
fan. The main purpose of this control method is to keep the fan off until
warm air is available, so that cold air will not be blown into the heated
spaces.
A damper that must throttle air flow should have:
Opposed blade operation
Where throttling is required, a damper having opposed operation should be
used. In this type of damper, adjacent blades rotate in opposite directions,
resulting in a series of slots that become increasingly narrow as the
damper closes.
. A pressure regulator is constructed so that a rise in ____________ steam pressure
reduces off the inlet flow of supply steam.
Downstream
. A vacuum breaker is used to avoid which of the following:
Negative gauge pressure
A vacuum breaker is designed to prevent the pressure in the condensate
return from dropping too low. If system pressure drops below 15 in.Hg, the
breaker opens and lets air into the system. Since the pump draws from a
tank that is vented to the atmosphere (to allow air to escape), it will
typically see atmospheric pressure at the inlet and will be unaffected by
system pressure.
If the R value on a section of insulation is 8, what would the value be when
saturated with water?
0
The R value of the insulation when it is saturated with water has no
insulation value.
In a RTD (resistance type device), as temperature increases, resistance will:
Increase linearly
The three main classifications of temperature sensors are: RTD (resistive
temperature device), thermistor, and thermocouple.
• RTD’s generally increase resistance linearly as temperatures
rises (positive temperature coefficient).
• Thermistors devices generally decrease resistance as
temperature increases and are less linear then RTD’s.
• Thermocouples create a voltage proportional to temperature
change. They are constructed using two conductors made from
dissimilar metals that are connected at one end. This junction
point forms the tip of the temperature probe. Thermocouples
are highly versatile and can be adapted for use in many
applications.
Why is a surge suppressor used on a contactor coil?
To prevent damage to the control circuit
What is a Surge Protector?
A device that shields computer and other electronic devices from surges in
electrical power, or transient voltage that flow from the power supply.
Standard American voltage for home and office buildings is 120 volts.
Anything over this amount is considered transient and can damage
electronic devices that are plugged into an outlet. Even though power
surges are so brief that they are measured in nanoseconds, they can cause
considerable damage to electronic equipment.
A minimum evacuation level for an air conditioning system is:
500 microns.
A vacuum pump capable of removing the atmosphere down to a very low
vacuum is necessary. The vacuum pumps usually used in the refrigeration
field are manufactured with rotary compressors. The pumps that produce
the lowest vacuums are two-stage rotary vacuum pumps. These vacuum
pumps are capable of reducing the pressure in a leak-free vessel down to
0.1 micron. It is not practical to pull a vacuum this low in a field-installed
system because the refrigerant oil in the system will boil slightly and
create vapor. The usual vacuum required by manufacturers is
approximately 500 microns, although some may require a vacuum as
low as 250 microns.
One horsepower is the same as
746 watts
Power and Energy
Power means a rate of doing work. A common unit of mechanical power is
the horsepower. For example, a ten-horsepower motor can do mechanical
work, be it hoisting an elevator or turning the shaft of a compressor, at a
faster rate than can a one-horsepower motor. The unit of power in the
electrical circuit is the watt. It is equal to the voltage multiplied by the
current.
The formula is: Power = Voltage X Current or Watts = Volts X Amperes
A common unit of electrical power is the kilowatt which is 1000 watts.
Electrical power may be converted into mechanical power in an electric
motor, or it may simply be turned into heat in a resistance. Equivalents
are as follows:
One kilowatt (KW) = 1.34 horsepower
One watt = 3.413 Btu per hour
One horsepower is 746 watts
Energy is the amount of work done or explained. It is the product of the
rate of doing work multiplied by a length of time during which work is
done. The watt is the rate at which work is done electrically. The common
unit of electrical energy is the watt-hour, this being a measure of the
electrical energy consumed in one hour.
One watt is equivalent to
3.413 Btu
Power and Energy
Power means a rate of doing work. A common unit of mechanical power is
the horsepower. For example, a ten-horsepower motor can do mechanical
work, be it hoisting an elevator or turning the shaft of a compressor, at a
faster rate than can a one-horsepower motor. The unit of power in the
electrical circuit is the watt. It is equal to the voltage multiplied by the
current.
The formula is: Power = Voltage X Current or Watts = Volts X Amperes
A common unit of electrical power is the kilowatt which is 1000 watts.
Electrical power may be converted into mechanical power in an electric
motor, or it may simply be turned into heat in a resistance. Equivalents
are as follows:
One kilowatt (KW) = 1.34 horsepower
One watt = 3.413 Btu per hour
One horsepower is 746 watts
Energy is the amount of work done or explained. It is the product of the
rate of doing work multiplied by a length of time during which work is
done. The watt is the rate at which work is done electrically. The common
unit of electrical energy is the watt-hour, this being a measure of the
electrical energy consumed in one hour.
One kilowatt is equivalent to
1,000 watts
Power and Energy
Power means a rate of doing work. A common unit of mechanical power is
the horsepower. For example, a ten-horsepower motor can do mechanical
work, be it hoisting an elevator or turning the shaft of a compressor, at a
faster rate than can a one-horsepower motor. The unit of power in the
electrical circuit is the watt. It is equal to the voltage multiplied by the
current.
The formula is: Power = Voltage X Current or Watts = Volts X Amperes
A common unit of electrical power is the kilowatt which is 1000
watts.
The purpose of the external equalizer line used with a thermostatic expansion
valve is to compensate for:
Refrigerant friction through the evaporator
The External Equalizer
Superheat is abnormally high and serious loss of evaporator
capacity results if the evaporator has any appreciable pressure
drop. You might feel that you could compensate for the evaporator
pressure by simply adjusting the valve, but this will not give the
correct answer because the evaporator pressure drop varies. This
pressure drop is due to friction developed when the refrigerant
flows through the evaporator, just as friction is developed when a
fluid flows through an ordinary pipe. Pressure drop at partial loads
will be considerably less than at full load because of the smaller amount of
refrigerant flowing at the lighter loads.
The variable evaporator pressure drop is corrected for by sensing
evaporator pressure, not at the evaporator or valve inlet, but at the
evaporator outlet. This is done with a connecting tube called an external
equalizer line, and is connected to a suitable fitting on the expansion valve.
Such a fitting on an expansion valve should never be capped or plugged. If
the valve has an external equalizer connection, an external equalizer line
must be installed. The line should be connected to the suction line as close
as practical to the bulb; specially, there should be no elbows, or other
fittings which increase flow friction, between the equalizer line connection
and the bulb. The purpose of the external equalizer line is to be able to
sense suction pressure at the point where the bulb is located. In this
respect, you should consider that it is possible for some liquid refrigerant
to flow from the valve, through the equalizer line into the suction line.
Since any liquid will vaporize at that point, the resulting cooling effect
could influence the temperature sensed by the bulb. To avoid this, the
equalizer line should connect to the suction line at a point a little
downstream from the bulb.
Cleaning refrigerants to ARI 700 standards is called:
Reclaim
The unit of measure for the specific volume of air is:
FT 3/LB
An important concern of air conditioning systems is the quantity
of heat that a system can add or remove.
The amount of heat removed by evaporating one pound of water in an evaporative
cooling tower is approximately:
1000 btu
Which of the four lifting sling configurations shown below creates the greatest
amount of load strain on the sling
C
. The components marked “B” would be called the
Motor Contacts
Which of the following plans are typically NOT supplied in a complete set of
Building Plans?
As Builts
Common Relay configurations are
(SPST) Single Pole Single Throw
(DPDT) Double Pole Double Throw
The __________ is a device that allows the use of a low voltage power source to
operate a high Current load powered device.
Contactor
When troubleshooting a contactor in a system. One should check the contact
surfaces for:
Pitting
Wear due to arcing
Terminals “A” would be labeled
L1,L12,L3
The terminals marked “D” would be labeled
T1,T2,T3
Pushing P1 down energizes
M1 First
A (VFD) Variable Frequency Drive controls all but?
Motor Life
Three general categories of motor starter problems include all except:
Sizing
VFD’s can be tested when ___________ by means of __________ Measurements for
various sections.
Energized, Voltage
If the value of R1 is lowered, the current
Increases
If resistor R2 burns open, the current
Goes to zero
If the value of R3 is raised, the current
Decreases
All Screw compressors consist of 2 Rotors
One male and one female rotor
Capacity control for a helical screw compressor is done by?
The Slide valve
Motor Speed
If resistor R3 is shorted out the current
Increases
If the voltage goes up in a resistive circuit, the current
increases
If you find yourself at odds with a confrontational customer, you should
Keep your cool, learn as much as possible, but call your
supervisor to report the incident
For applications where quiet operation and light axial load characteristics are
found, the type of bearing normally used is the:
Sleeve bearing
Sleeve bearings with the oil port lubrication system must be lubricated with the
proper oil because
Oil that is too thin will allow the shaft to run against the bearing surface.
Oil that is too thick will not run into the clearance between the shaft and the bearing surface.
The correct oil allows the tor shaft to float on a film of oil between the shaft and bearing surface.
Too much grease in grease lubricated ball bearing
Cause Overheating
. A ladder must extend above the edge of a roof by at least ______ ______.
3 Feet
The proper angle for a ladder is achieved when the distance of the ladder from the
building at the base is about __________ the working length (height) of the ladder.
1/4
. Air handling systems that employ economizers which permit outside air “free
cooling”
Are most economical when controlled by an enthalpy controller
When face and bypass dampers are used on systems with direct expansion cooling
coils:
Compressor capacity control is required
The rate of flow of electrons in a circuit is termed:
Amperage
“Pressure” differential in an electrical resistance is the:
Voltage
The unit used to measure electrical resistance is the:
Ohm
The four essential parts of the vapor compression cycle compressor, condenser,
evaporator and:
Expansion Device
How is an anticipator connected to a single contact cooling thermostat?
In parallel with contact
The process of removing moisture from air is called:
Dehumidification
Basic types of air supply outlets are:
Grilles
Three basic types of air supply outlets are:
- Grilles
- Slot diffuser outlets
- Ceiling diffusers
With reference to copper tube, what is meant by the letters ACR?
Air conditioning and refrigeration tube
How is the heat anticipator wired in with heating contacts on a 24 volt space
thermostat?
Series
A piece of ice weighs 20 LBS and its specific heat is 0.49. It will require
__________ Btu to heat the piece of ice from 27 degrees to 31 degrees F.
39.2
Solution: Use for Formula: Heat (Btu) = Weight (pounds) x Specific Heat (Btu per LB per degree F) x Temperature Difference (degrees F) = 20 x 0.49 x (31-27) degrees F = 20 x 0.49 x 4 = 39.2 Btu
Given a rate of air flow of 2250 cfm in a duct having a cross-section 18 inches by
18 inches, the duct velocity should be ___________ fpm.
1000
V = 144 x cfm divided by a
= 144 x 2250 (324,000) divided by 18 x18 (324) = 1000 fpm
If a refrigerant sight glass shows bubbles, you know:
There is gas in the liquid
A liquid refrigerant receiver has two liquid level test cocks, one near the top of the
receiver and one near the bottom. If the system contains enough refrigerant,
when the lower cock is opened:
The test cock should discharge liquid refrigerant.
Desiccants are used in:
Driers
Only __________% of the direct radiation at the edge of Earth’s atmosphere
reaches the Earth’s surface.
51
Collectors should face as close as possible to ___________?
True South
_________ occurs in a Solar Thermal System when the heated transfer fluid
within the absorber piping rises within the collector and is replaced by cooler fluid
downstream.
Convection
A (n) ___________ system uses a Heat Transfer Fluid and heat exchanger to
transfer heat to the Domestic Hot Water without the use of mechanical means to
circulate the HTF.
Passive indirect
Self-pumping Systems are _________ systems.
Passive Direct
The vacuum pump used in vacuum steam heating systems that creates a
vacuum using high velocity water is the:
Jet Type Pump
Vacuum pumps used in vacuum steam heating systems can be destroyed if
they are made to pump:
by cavitation
&
Steam.
A common reason for pump failure is live steam entering the pump due to
failed steam traps. The cause of the pump failure must be corrected at the
same time the pump is repaired or replace. If bad steam traps allowed the
steam to reach the pump, the steam traps must be repaired or replaced or
the new pump will soon fail again
If a vacuum pump in a vacuum steam heating system burns out, a very
common cause is:
A failed steam trap.
Effective recovery of condensate reduces the following cost of making steam:
Fuel/energy costs associated with producing steam Other costs are also saved.
Boiler water make-up and sewage treatment.
Boiler water chemical treatment.
A symptom of a failed steam trap is:
A trap that is warmer than condensate temperature.
When entering a customer residential premises you should always
Place a clean pair of disposable covers over your shoes
If the technician is on a service call and notices another potential problem not
related to the current work order, what should the technician do?
Discuss what you have with the customer and your supervisor
so that the customer can decide whether to authorize the additional repair
Which of the following is required part of the work order?
Form completed in legible hand writing
Complete list of materials used and amount of time spent on the job
Getting the customer to sign the work order should be
The last thing that you should do before leaving the job
Which of the following is a part of your responsibility relative to your work
crew?
Working safely on the worksite
The maximum desirable operating temperature of a ball bearing is
180 degrees F.
Shaft runout can be measured with
A dial Indicator
A Runout Gauge
The seal in a compressor is necessary to prevent
Refrigerant from leaking out the rotating shaft.
Oil from leaking out at the rotating shaft.
The mating seal surfaces on a sleeve type rotary bellows seal are:
Polished steel surfaces and a carbon ring
With belt driven equipment, alignment of the motor and driven equipment
pulleys
Is accomplished using a string or straight edge.
A lock and tag may only be removed by the employee that applied it, unless
the employee is absent from the workplace, then the lock or tag may be removed
by a qualified person designated by the employer to perform this task provided
that the employer ensures that ___________________________________.
The employee who applied the lock or tag is not available at the workplace.
The employee who applied the lock or tag is aware that
it has been removed before he or she resumes work at that workplace.
Section 608 of the Act prohibits you from knowingly venting ozone-depleting
compounds used as refrigerants into the atmosphere while maintaining,
servicing, repairing, or disposing of air-conditioning or refrigeration equipment
(appliances). The prohibition went into effect on ____________.
July 1, 1992
When working on a HCFC-22 appliance, or isolated component of such
appliance, normally containing 200 pounds or more of refrigerant and using
recovery or recycling equipment manufactured or imported on or after November
15, 1993, you are required to evacuate to a level of
10 In HG.
If a compressor burn has occurred, the refrigerant must be ____________
Recovered
Reclaimed
An advantage of the inverted bucket trap is that:
It also vents air and carbon dioxide continuously at steam
pressure.
Flash steam is caused by:
Pipe friction
Reduced pressure
A vertical rise in a condensate line
The purpose of a drip leg in a steam line is to:
Let condensate escape by gravity from the fast-moving steam.
Store condensate until it can be discharged through the steam trap.
Inadequate trapping of steam mains often leads to:
Water hammer and damaging slugs of condensate.
Pressure in a vertical position condensate pipe will drop 1 psi for every ______
feet in elevation. This is an important factor, since boiling temperature drops as
pressure drops. When elevating condensate, this drop in pressure can cause flash
steam.
2.31
When using a listening device to test a steam trap, what would the technician
listen for that could indicate a problem.
High velocity sound.
If an inverted bucket steam trap is blowing live steam, what might the trouble
be?
The valve may have failed to seat because of wear or a piece of dirt or scale.
The trap may have lost its prime.
The bucket is stuck or has a hole in it
The ____________ drains the condensate from the steam header and returns it
to the boiler below the water line while preventing the boiler water from flowing
out of the boiler into the return line main.
Equalizing line
The ____________ is designed to protect boilers against the loss of water due to
leaks in the return line.
Hartford Loop
The control valve in a sub-atmospheric steam heating system is limited to
approximately ______ % change per minute.
3
The control valve is designed with a small percentage of change so there
are no radical changes in the pressure and steam temperature in the
system piping.
What is the most common cause of valve noise?
Valve piped incorrectly
When the discharge of one compressor is piped into the suction of another
compressor, it is called a:
Two stage system
What is the most common cause of valve noise?
Valve piped incorrectly
If too much refrigerant is being fed to the evaporator ____________.
The superheat will be low
The low pressure cap tube of an oil failure switch should be connected to the:
Compressor crankcase
When copper tubing is being brazed, nitrogen gas can be purged through the
system to prevent:
Oxidation inside the tubing
Erection of Refrigerant Piping Systems Using Copper T
In an economizer, an enthalpy control regulates the use of outdoor air on the
basis of the air’s:
Humidity and temperature
When removing the gauge port plug from a compressor discharge service
valve, the valve should be:
Back seated
An acid test kit is used to test acidity of:
Oil
The TXV sensing bulb is mounted:
On the suction line as it leaves the evaporator
In an air cooled system with capacity control, compressor unloading will cause
the:
Suction pressure to rise and the discharge pressure to fall
A lamp has a source voltage of 110 volts and a current of 0.9 amperes. What is
the resistance of the lamp?
122.2
Solution: Ohms Law
R=E divided by I
110 divided by 0.9 = 122.2 ohms
The amount of heat removed to lower the temperature of 15 lbs. of water from
48 degrees F to 39 degrees F is:
135
Solution: Heat = Weight (lbs.) x Specific Heat (btu/lb. per degree) F x Temperature Change (degrees F) = 15 x 1 (48-39) degrees f = 15 x 1x 9 = 135 Btu
A belt-driven fan is to turn at 580 rpm. If the fan is driven by a 1740 rpm
motor and the motor has a pulley with a three-inch pitch diameter, the fan pulley
should have a pitch diameter of ___________ in.
9
Solution: RPM x D = rpm x d
580 x D = 1740 x 3 (5220)
D = 1740 x 3 (5220) divided by 580
= 9 in
Using a rule-of-thumb figure, approximately how much heat, in Btu/hr., must
be rejected by the condenser when the net refrigerating effect is 25 tons?
375,000
Solution:
“Rule-of-thumb” figure for condenser heat rejection is 15,000 Btu per ton of
net refrigeration effect.
25 tons x 15,000 Btu per ton = 375,000 Btu per hour
The heat transferred by calculating water can be expressed by the following
equation:
Btuh = 500 x gpm x delta T
A particular heat exchanger is supplied with circulating chilled water flowing at a
rate of 100 gpm. If heat is added to the water at a rate of 500,000 btuh when the
initial (entering) water temperature is 40 degrees F, at what temperature does
the water leave the heat exchanger?
50
Solution: Btuh = 500 x gpm x delta T 500,000 = 500 x 100 x delta T Delta T = 500,000 500 x 100 Delta T = 10 Leaving temperature = 40 + delta t Leaving temperature = 40 + 10 Leaving temperature = 50 degree F
