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
Pay attention to N.C. pressure switch at top of picture
