UA Star Exam Flashcards
For VAV control what device is needed for proper operation
Static pressure sensor
In a balanced three phase system, the phase the voltage waveforms differ in phase by?
120 degrees
Which of the following government agaencies is responsible for the regulations dealing with the transportation of hazardous material?
DOT
What pressure does a steam system need to operate below to be considered “low pressure”
15
The purpose of combustion testing is to perform all except which of the following?
A. condition of air through the air handler
b. Detect unsafe conditions
C. leak in the system
D. poor heat transfer
condition air through the air handler
During a standing vacuum test, the system goes from 500 microns to 2000 microns and then stops. Which of the following is the most likely cause
moisture in the system
On a typical split phase motor the start winding circuit is de-energized as it reaches approximately ______ of it’s operating speed
75%
Which of these is an example of a halogen?
CFC refrigerants
Which of these is the part of the centrifugal pump that spins and forces water through the system?
impellar
The mechanical seal in a centrifugal pump is necessary to prevent which of the following events
Fluid leaking out around the shaft
With belt driven equipment, alignment of the motor and driven equipment pulleys
Is accomplished using a string and straight edge
One horsepower is equivalent to
746 watts
The length of the pipe (drip connection) that is needed to overcome the pressure drop in a one pipe gravity return steam heating system and return condensate to the boiler is
28 inches
Air is eliminated from a sub atmospheric system by
Vacuum pump
What is the maximum safe amperage draw of the secondary winding of a 40 va transformer output of 24 volts
1.67 amps
Outdoor reset of hot water temperature for heating results in which of the following
Hottest water during the coldest weather
Sleeve bearing with the oil port lubrication system must be lubricated with the proper oil because
Oil that is to thin will allow the shaft to run against the bearing surface
Oil that is to thick will not run into the clearance between the shaft and the bearing surface
The correct oil allows the shaft to float on a film of oil between the shaft and bearing
The boiler should ______ while testing low water cutoff safeties
autmatically shut down
If a pressure gauge reads 5 psig at sea level elevation, the corrosponding absolute pressure is?
19.7
5psig + 14.7psia
Which boiler can be brought through standard doorways and assembled in place
Cast iron sectional
Residential air conditioning piping should be sized according to which of these?
manufacturers instructions
VA is the common term for
Watts
Volts times amps=VA
The type of refrigerant that must be used now
HFC
On centrigual pumps, if it is ever necessary to reduce pump flow temporarily, do so using which method?
throttle the discharge
Vacuum pumps used in vacuum steam heating systems can be destroyed if they are made to pump?
Air Steam
The approach temprature for the evaporator is
The difference in the refrigerant boiling temprature and the leaving water temerature
On a refrigeration system where the evaporator is located below the compressor, how are suction risers sized?
smaller for high velocity
A symptom of a failed steam trap
A trap that is warmer than condensate temperature
Evaporator approach on a centrifugal water chiller is determined by calculating the difference between?
evaporator leaving water temperature and saturated evaporator temperature
Which control should be installed on an air handler which brings in outside air through a steam coil?
freeze stat
When the motor of a two-wire spring return actuator is operating, what is happening with the spring?
it is being wound up
Theoretically, a pump can raise water by suction approximately ————— feet vertically
34 1’ of water .433lbs
How should the belts in a multiple V-belt application be replaced
as a set
It is not uncommon for residential furnaces to approach AFUE levels of
96%
What is the maximum safe amperage draw of the secondary winding of a 60 VA transformer output of 12 volts
5 60 divided by 12
which system component is used to prevent all strip heaters from energizing at the same time?
sequencer
If not properly installed hot gas muffler might trap
Oil
In the hot gas bypass control metho, which system component is bypassed?
condenser
Which instrment is needed to check the freeze protection level of a solar hydronic system?
refractometer
Before you work on an electrical circuit
Check voltage with a good meter
Getting the customer to sign the work order should be?
The last thing you should do before leaving the job
The amount of heat rejected by the condenser of an air conditiong system is typically ________ the amount of heat absorbed in the systems evaporator
25% or greater
Where is the expansion valve located in the refrigerant system
In the liquid line at the entrance of the evaporator
A vacuum breaker is used to avoid which of the following
Negative gauge pressure
Overheating a joint when brazing a wrought copper fitting causes
Oxidation and distortion of the joint
The instrument used for finding humidity levels in the atmosphere is
Sling psychrometer
As a rule, the best general type of air diffuser to use in a variable air volume system is
slot diffuser
What is the kw rating of the following heat element
resistance of element 20 ohms
voltage applied 277v
E squared divided by R= p divide 1000 for kw
E=volts
R=resistance
I=amps
P=watts
3.8kw
which of the following instruments is used to verify water flow across the chiller barrel
differntial pressure switch
Which is the most accurate tool to use when measuring evacuation levels
Micron gauge
A thermostatic steam trap that fails in a closed postiion may cause which problem to a heating unit?
water logged
A tire style coupling is commonly used on which of these
Cooling towers
A thermocouple is constructed from which of these materials or components?
two dissimilar metals welded together
what is the purpose of a bypass on a steam regulator
maintains steam pressure if the regulator fails
When copper tubing is being brazed, nitogen gas can be purged through the system to prevent which of these events?
oxidation inside the tubing
Materials which do not allow their electrons to spin out of orbit easily are called
Insulators
A refrigerant system has a hand operated needle valve for the refrigerant expansion device. If refrigerant load and suction pressure remain constant, a decrease in condensing temperature will?
Result in reduced refrigerant flow unless the valve is opened
Copper plating of compressor parts is?
Caused by contaminants in the system
Which of these may be caused by an oversized vapor line in a refrigerant circuit?
poor oil return
When meassuring the winding resistance of a split phase compressor motor, the smallest value will be meassured between?
The run terminal and common terminal
The first thing a service mechanic should do before performing service work on refrigeration equipment is to
Locate the disconnect
Which is the first step of shaft alignment of a direct drive motor
Angular in elevation
What should you do if a customer refuses to sign a work order?
note it on the ticket and call your supervisor
which of the following is a common cause of back pressure in a condensate return line
failed steam trap
When two run capacitors having values of 15 MFD and 10 MFD are connected in parallel what is the combined value?
25 MFD
what is the rule of thumb in BTU per hour of heat rejection of a condenser
15,000
Face and bypass dampers should be adjusted to provide
Tight shutoff to reduce the possibility of overcooling or overheating
Flash tanks utilize which of the following?
A. Condensate
B. Flash Steam
C. Subcooled Steam
D. superheated steam
condensate
An acid test kit is used to test acidity of
oil
Why is it necessary to use static wrap when replacing circuit boards
To prevent component damage
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
one fourth
What is the purpose of a slide valve on a helical rotary screw compressor
to provide capacity control
When chocking a piece of equipment with a sling where should you run the sling
Through the Clovis attached to the eye
Why is a surge suppressor used on a contact coil
To prevent damage to the control circuit
Which of these is the tool to use to move a coupling half that is seized on the motor shaft
Hammer with softening tool
With refernce to copper tube, what is meant by the initials ACR?
air conditiong and refrigeration tube
A system containing one cooling tower, one water cooled condenser, and one pump is classified as which type of system?
closed
To assist customers in making an informed choice when purchasing unitary air conditioning equipment, the efficiency is expressed as Energy Efficiency Ratio (EER or SEER) the units of which are?
Btuh/watt
How many BTU are there in 8kw of electrical power
27,304 3413 times 8kw
Which of the following is not a basic type of air supply outlet?
barometric damper
when the discharge of one compressor is piped into the suction of another compressor it is called
two stage system
Condensate in steam lines could result in
water hammer
In starting up a chilled water system the first piece of equipment to start should be
Chilled water pump
A cylinder recovery tank with a service rating of DOT _____ psig is required for R410a
300 psig
To check for angular alignment use a_______ gage or _________ gage at all four points
Taper or feeler
The symbol below would indicate a _________ switch
Temperature actuated
Air handling systems that employ economizers which permit outside air “free cooling”
Are most economical when controlled by an enthalpy controller
Bubbles in a refrigerant sight glass are an indication of what condition?
there is vapor mixed with the liquid
Operation of the potential relay is based on which of these principles
motors develop counter EMF
Installation or connection diagrams most closely resemble
Wiring diagrams
When troubleshooting a contactor one should look for
pitting
wear due to arcing
If used to drip the end of a steam main, the type of steam trap that would require a cooling leg is
Thermostatic
Current flowing in one direction for a split second and then in the other direction for a split second would be the defenition of?
Alternating Current
In a vapor steam heating system, condensate is returned to the boiler by means of
Boiler return trap
The maximum desirable temperature of a ball bearing is
180 degrees F
A water coil generally should be piped to provide _____ flow
counter
Outdoor reset of hot water temperature for heating gives
Hottest water during coldest weather
If you were on a job and ran out of 5/8” O.D. fittings while installing 5/8” ACR tube which of the following sizes of copper water tube fittings could be used?
1/2”
Which is the fastest way to totally recover refrigerant
push pull method
When copper tubing is being brazed, nitrogen gas can be purged through the system to prevent
Oxidation inside the tubing
Formula for measuring the sqft of round duct
Diameter divided by 2= radius
Radius squared
sum of radius squared times 3.14(pi) equals sq inches
sq inches divided by 144 equals sq ft
sqft times length of duct
Suction risers are typically reduced by one size over that of the main suction run
To increase refrigerant velocity and aid in oil return
What Device could be used as external protection for a motor?
A. Line Fuse B. A circuit breaker C. Magnetic overload
What length of pipe (drip connection) is needed to overcome pressure drop in a one pipe gravity return steam heating system and return condensate to the boiler?
28 inches
A dual element fuse has
A thermal cutout and a normal fuse link
The two planes of alignment that must be considered when aligning a flexible coupling are
Parallel and angular
When soldering copper tube, after the tube and fitting are cleaned and fluxed, how soon should they be soldered?
as soon as possible
Which of the following is required part of the work order
Form completed in legible hand writing Complete list of material used
What is used to measure the freeze point of glycol
Refractometer
The pump motor on a condensate receiver is usually started by
High condition in the receiver
If the water flow to a water-cooled condenser is reduced, the temperature difference across the condenser will?
Increase
On an intermittent pilot system, when is the pilot light on?
through the main flame cycle
A sleeve bearing would typically be used in a motor that
Operates with a light load and where noise is a factor
Suction line filter dryers are usually equipped with gage connections so that pressure drops can be determined. Why?
So that you can determine when to change the filter-drier
Basic types of air supply outlets are?
Grilles
For applications where quiet operation and light axial load characteristics are found, the type of bearing normally used is
Sleeve bearing
Which is true when a load is to be lifted with a sling?
All sharp edges should be padded
Which government agency requires the display of the AFUE rating on equipment
Federatl Trade Commision
To prevent priming in a steam boiler, the horizontal steam main should be a minimum of what distance above the NOWL?
24 inches
What device is used to energize another load such as a contactor or motor starter which in turn would start or stop a motor
A pilot duty relay
A pressure regulator is constructed so that a rise in ___________ steam pressure reduces off the inlet flow of supply steam
Downstream
The type of traps normally used on steam radiators are?
Thermostatic traps
Which of the following government agaencies regulates the certification of refrigerant cylinders?
DOT
A single phase motor in which the run capacitor remains connected when the motor runs is called
Permanent split capacitor motor
Air is eliminated from a vapor system by
Air eliminator
The run load amprege on an electric motor is typically
1/5th tha of full load amprege
The evaporator in a refrigerant system
Is the component where refrigerant boils and absorbs heat
which of the following devices changes energy from one form to another
transducer
Solar _____ is the amount of solar thermal energy produced divided by the water heating energy demand of the building
Fractional
In a gas fired warm air furnace, the furnace fan should be?
controlled by furnace bonnett temperature
When should vacuum pump oil be changed?
Every 100 hours
A lockout relay should dropout when
An overload relay opens
A loose fitting belt on a belt driven device will cause?
Worn pulley grooves
A flame sensing relay strategy that takes advantage of the fact that hot gasses in a flame become ionized and conduct electricity is called a
flame rod
A piece of ice weighs 20 lbs and it’s specific heat is .49 It will require ______ btu to heat the piece of ice from 27 degrees to 31 degrees
39.2
Heat (btu)= weight (pounds) x specific heat x delta t
20 x .49 x (31-27)
20 x .49 x 4
39.2 btu
Condensate traps on a draw through evaporator coils in order to prevent
Water overflow
Pay attention to N.C. pressure switch at top of picture
Which of the following is not a symptom of a water logged exansion tank?
erratic burner operation
In an air cooled system with capacity control , compressor unloading will cause
suction pressure to rise and discharge pressure to fall
Relays are made up of a _____ and one or more_____
switch, loads
In a float and thermostatic trap the float rises to discharge
Condensate
For which purpose are lockout relays used in air conditiong systems?
prevent compressor short cycling
The device that could be used to regulate the discharge pressure of a condensate pump is
Plug cock
A thermostatic steam trap that fails in the closed position would cause a heating unit to become
Waterlogged
energy efficiency ratio is a meassure of the
realative efficiency of the heating or cooling appliance
What is the purpose for installing a vaccum breaker valve in an automatically controlled steam heating system
it limits the vacuum to the pump and prevents vacuum to the system
The boiler return line is connected to the steam main by
equalizing line
Which solution should be used for chemically cleaning a condenser?
Hydrofouric acid
AFUE stands for
Annual Fuel Utilizaton Efficiency
An air filter with a merv 6 rating or higher will reduce levels of small particulates and improve indoor air quality. MERV stands for
minimum efficiency reporting
Saturated liquid line pressure minus liquid line temperature is equal to which of these?
subcooling
A minimum evacuation level for an air conditioning system should be
500 Microns
The amount of heat removed by evaporating one pound of water in an evaporative cooling tower is
1000 Btu
Which of the following is not a type of steam trap?
A. F&T
B. Mechanical
C. Thermo Disc
D. Thermostatic
mechanical
A full voltage starter has
One contactor
Which device is used in a refrigeration system to protect the compressor from liquid slugs
Suction Accumulator
Which of the following components is used to prove fan operation before electric duct heaters are energized?
sail switch
Which of the following gases must never be used to pressurize or leak test a refrigeration system
oxygen
In order to return condensate to a boiler, the height of the water column needed to overcome the pressure drop in a two pipe gravity return system is
28 inches for each pound of pressure the boiler is producing
One type of pressure sensing device uses a flattened metal tube, which is bent into a part circle with one end fixed in place and connected to a system to be measured. The other end of the tube is closed and free to move. An increase in pressure tends to straighten the tube. The movement of the free end of the tube is connected to a dial that reads pressure. This type of gage is called a?
Bourdon tube
If a split phase motor turns in the wrong direction, it’s direction of rotation can be reversed by this action?
interchaning the starting winding leads
What is the acceptable voltage output of a thermocouple in a standing pilot boiler?
20-30 mV
Which of these is not a step that should be taken before starting a pump?
remove coupling guard
Lock out relays in an air conditioning system are used to?
Prevent compressor short cycling
A full voltage starter energizes which of these
all contactors
Defective rigging equipment and hardware should be
Destroyed
Which of the following is not correct when working with an ocy acetylene torch set?
use grease or oil in the hose and regulator threaded connections
A VFD controls all but
Motor life
which device is used to stop the flow of liquid or vapor in a refrigerant system
Solenoid Valve
Potential difference refers to the energy difference in electrons between two reference points meassured in which type of unit
Volts
An acid test kit is used to test the acidity of which of the following?
oil
Which of the following statements is not true of a desiccant type heat recovery system?
it created higher loads than traditional airside economizers
Which of these causes a boiler feed pump to cycle on?
boiler feed pump controller
An evaporative cooling tower’s bleed rate is adjusted to maintain?
The desired concentration of total dissolved solids
Shaft runout can be measured with
A dial indicator A runout gage
which of the following is an analog input
temperature sensor
The pump motor on a boiler feed pump is started when there is
A low water condition
Follow which of these methods when adjusting a gas regulator to increase outlet pressure
Adjust clock wise to increase
An excess of acetylene in an oxy-acetylene flame will give an
Carburizing flame
Fire stats located in the airstream of air handling units
Are required in both supply and return Should be the manual reset type Should be non adjustable
__________ are used to control ventilation by monitoring the outdoor temperature and humidity
Economizers
Refrigerant is compressed through a scroll compressor _________ of the scrolls
Outside to center
Which of the following is a part of your responsibility relative to your work crew
Working safely on the worksite
To produce electromagnetisim, relative motion is required between a magnetic field and a?
Conductor
How is the heat anticipator wired in with heating contacts on a 24 volt space thermostats
in series
A cooling anticipator is wired in parallel
Thrust loads are ______ to a shaft
parallel
Basic types of heat pumps, classified as their heat source and the medium being heated, include all except whichh of the following?
water to air to water
The purpose of the external equalizer line used with a thermostatic expansion valve is to compensate for
Refrigerant friction through the evaporator
The device that is used to maintain a pressure differential between the supply and return pipping in a sub atmospheric steam heating system is a?
Differential controller
The water loop on a water to ground geothermal loop is typically made out of which type of material
PVC
What does CPR stand for?
Cardio Pulmanary Resuscitation
If the thermal bulb on the TEV comes loose from its mounting at the outlet of the evaporator which of the following will occur?
the valve will open, feeding more refrigerant into the evaporator
Identify reverse rotation of a scroll compressor by
the compressor will not compress
compressor will trip on overloads
If a vacuum pump in a vacuum steam heating system burns out a very common cause is
A failed steam trap
The heating capacity of an air to air heat pump
decreases as outdoor air gets colder
Unless equipped with OSHA or CSA approve ground fault circuit interrupters, portable electric lighting used in wet and or other conductive locations as, for example drums, tanks and vessels, shall be operated at _____ volts or less.
12
When using using an oxy acetylene torch for brazing the flame should be adjusted to provide
Oxidizing flame
The portion of the electromagnetic spectrum to which solar collectors respond is ______ and near infrared radiation.
Visible Light
Closed transition starting means
The motor is never disconnected from the line during starting
To freeze one pound of water _______ BTU of latent heat must be removed
144
A screw compressor consist of 2 rotors
one male and one female rotor
The unit used to meassure electrical resistance is
Ohm
Electrical Pressure is meassured in
Volts
The rotation of a three phase motor can be reversed by interchanging
Any two leads
What is the acceptable temperature drop across a liquid line filter drier?
less than 2 degrees
The two planes of alignment that must be considered when aligning a flexible coupling are
Parallel and angular
A common leak detection device for refrigerant
Halide torch
Thermostatic traps are opened and closed by
Flexible Bellows
The unit of meassure for a specific volume of air is
FT 3/lb
Unit ventilators are usually equipped with outside air dampers to
Comply with most local and state codes
Provide ventilation during occupancy
Starting relays are not used by which of the following motors
PSC
With an electric motor running normally at full load amp reading would be called
Run load amprege
What is the acceptable annual leak rate of a process cooling system if the circuit contains more than 50 pounds of refrigerant
35%
Cleaning refrigerants to ARI 700 standards is called
Reclaiming
When connecting rigging to equipment, where should the connection be made?
per equipment manufacturers instructions
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
The purpose of a suction line accumulator
Trap liquid refrigerant
A ladder must extend above the roof by atleast
3 feet
The device used to actuate the vacuum pump in a vacuum steam heating system when there is a loss of vacuum in the system return pipe is the
Vacuum switch
The amount of heat removed by evaporating one pound of water in an evaporative cooling tower is approximately how many BTUs?
1000
A lamp source has a voltage of 110 and a current of 0.9 amperes. What is the resistance of the lamp
122.2 110 divided by 0.9
Which of the following is a disadvantage of a Variable Refrigerant Flow system?
does not allow for future expansion
During flow switch installation the paddle must be
Fitted to the pipe
When calculating subcooling for an HFC refrigerant with a large temperature glide. which column on the pressure/temperature chart is used?
bubble point
Which of these should be worn to prtect the eyes when handling refrigerants?
chemical splash goggles
When soldering copper tube after the tube and fitting are cleaned and fluxed they should be soldered
As soon as possible
As compared to across the line starters, low voltage starters
reduce starting current in rush
Too much grease in grease lubricated ball bearing
casues overheating
which is the final step in installing a pillow block bearing
tighten bearing to shaft
For a compressor having a lubricating oil pump, the net oil pressure is equal to ______ pressure
oil pump discharge pressure minus compressor suction
In order to protect a load, safety limit devices are most often wired?
In series
If a mechanical seal has just been replaced and the pump leaks slightly at start-up, which step should you take first?
allow the pump to continue running for a short period to see if the leak stops
An important feature of a refrigerant reciever, in the case where the liquid line to the evaporator comes out of the top of the reciever, is a?
Dip tube
Which is true of the heating capacity of an air to air heat pump?
it decreases as outdoor air gets colder
The purpose of the compressor is to change
Low pressure low temperature vapor to a high pressure high temperature vapor
Mixing boxes are usually used with which types of system?
double duct system
Which of the following would prevent a successful pump alignment
Flexible base
what effect will a higher than rated supply voltage have on the current draw of an electric motor
It will be lower than it should be
If not properly installed a hot gas muffler might trap
Oil
which of the following is an analog output
VFD speed control
the rate of flow of electrons in a circuit is termed
Amperage
With belt driven equipment, alignment of the motor and driven equipment pulleys
Is accomplished using a string and straight edge
Which is a difference between a motor starter and a contactor
a starter has overload protection
cavatation in a pump pumping hot water
makes a pump noisy
Is the result of water boiling into steam
Is the result of insufficient NPSH
(NPSH stands for Net Positive Suction Head)
An entalpy control in an economizer regulates the use of outdoor air on the basis of the airs
total heat
Under which of the following conditions should you not use a megger?
within a deep vacuum
When installing split tapered bushings, where should you apply anit-seize lubricant
none of the parts
Which type of plans are not supplied in a complete set of building plans
As built
One watt is equivalent to
3.413 btu
Thermostatic traps are opened and closed by which device?
flexible belows
Fuses are sized by the _____ they can carry
Amprege and Current
The purpose of an evaprotor pressure regulator is to
Prevent a minimum pressure in the regulator
When water is introduced into the end of a chiller it is contained in
water boxes
While troubleshooting, it is found that on a call for cooling, the voltage across a potential realys contacts remains 0 volts, the compressor then cycles on its internal overload. which of the following is a possible explanation?
closed (welded) contacts in the potential relay
The device that is incorporated into a vaccum steam heating system to protect the vaccum pump from creating to low a vaccum is
Vaccum breaker
In starting up a chilled water system which should be the first piece of equipment to start?
chilled water pump
A bellows is used in
In both pressure and temprature controllers
A belt drive on a motor driven fan has a drive sheave of 3” pitch diameter on the motor. The sheaves of the fan shaft has a pitch diameter of 5”. When the motor speed is 1720 rpm, what is the fan speed?
Rpm of driven= diameter of driver X rpm of driver divided by
diameter of driven
1032 rpm
which of the following is not a type of steam regulator?
electric
Why is it desirable to have a pressure differential gauge to measure filter resistance?
to tell when the filters are dirty
When steam is superheated it’s
Temperature is increased with no increase in pressure
The device which forms a water seal that prevents raw steam from entering and damaging pressure gauges, vapor stats, pressuretrols, etc.
Pigtail
A direct expansion multi zone unit requires
Compressor capacity control
When performing routine maintenance on an economizer which of the following items do not need to checked
cooling anticipator
where is a bellows used?
only in tmperature controllers
What is the purpose of adding glycol to a solar heating system?
allow adequate freeze protection in low ambient conditions
In a muti blade louver damper when adjacent blades rotate in opposite directions, the damper is said to have ______ blade action
opposed
The ______ is a device that allows the use of a low voltage power source to operate a high current load power device
Contactor
Systems with 50+ pounds of refrigerant, annual leak rate cannot exceed?
50%
which of the following would happen if the vent port on a gas regulator is plugged
outlet pressure would be reduced
If the water flow to a water cooled condenser is reduced, what will happen to the temperature difference across the condenser?
It will increase
One kilowatt is equivlant to
1,000 watts
Which organization or department enforces the regulations of the clean air act?
EPA
The device that controls the steam pressure on the supply side of a sub atmospheric steam heating system is a?
Control valve
To improve their operating economy, multizone air handlers should
be used with a varible capacity squirrel cage fan
Have their hot deck temperature reset by outside air temperature or on the coldest zone demand
Which of these conditions could result from condensate in steam lines?
water hammer
When soddering a copper pipe connection which of the following processes allow for alloy to be drawn into the space between the copper tube and the fitting connection
Capillary Action
A pressure regulator is constructed so that a rise in ________ steam pressure reduces off the inlet flow of supply steam
Downstream
A refrigerant heat exchanger might cause
the compresser to overheat
Which of these is an instrument to be inserte into a duct for meassuring velocity pressure?
pitot tube
The amount of heat removed to Lower the temprature of 15lbs of water 48 degrees F to 39 degrees F is
135 Btu
Heat = Weight (lbs) x specific heat (BTU/lb per degree) F xTemprature
15x1 (48-39) degrees F
15x1x9
=135 Btu
Which of the following is not used to size gas regulators?
Type of ignition system
If not properly installed a hot gas muffler might trap which of the following?
oil
In a RTD (resistance type device), as termperature increases, resistance will
Increase Linerally
Capacity control on a helical rotary (screw) compressor is obtained using
A sliding vane
If the float in a f&t trap failed and filled with water , the trap would
Discharge steam continually
A bearing used on the bottom of a motor where the shaft is positioned vertically is called a _______ bearing
Thrust
A damper that must throttle air flow should have
Opposed blade operation
When using a capcity control compressor, which of these is a requirement for double suction gas riser?
allow for oil return to compressor during low load conditions
A rectangular duct measures 20” x 30” what is the area in square feet
20 times 30= 600
600 divided by 144
Electricity results from the movement of tiny negatively charge particles called
electrons
Varible volume systems
control space temperature by regulating the flow of air to each zone
if not properly installed a compressors discharge muffler malfunction in this way
trap oil
Cavitation can destroy a centrfigual pump, is noisy and is caused by
outlet pressure that is to high
The voltage rating of a motor controller holding coil is
Not necessarily the same as the motor supply voltage
In an economizer, an enthalpy control regulates the use of outdoor air on the basis of the airs
Humidity and temperature
The wall thickness of type k copper tube is
Greater than that of type l or type m
Which scenario would justify the addition of a heat recovery unit?
A. a building needs outside makeup air but HVAC equipment is marginally sized
B. A heating system holds the load of a garage but has long recovery time when overhead doors are opened
C. A homeowner in north dakota complains that thier heating system does not keep up with the outside air is below -10 degree F
D. a homeowner in San Diego needs makeup air when running an attic fan
A building needs outside makeup air but HVAC equipment is marginally sized
The mating seal surfaces on a sleeve type rotary bellows seal are
polished steel surfaces and a carbon ring
Receivers are usually required in systems having
Evaporative condensers
when a object is refrigerated
heat is removed from it
Which of the following does not need to be considered when converting from HCFC to a HFC
Thickness of the line tubing
the amount of heat removed to lower the temperature of 15 lbs of water from 48 degrees to 39 is
135
heat=weight x specific heat x delta T
