Refrigerant 2 Flashcards
- What is the minimum allowable refrigerant velocity in a reduced discharge riser?
1000-1500 fpm
What is the function of the “p” trap in vapour risers
Assists oil movement
What is the correct method to transfer HFC 404A for a refrigeration system?
. Removed as a liquid from cylinder and flashed into the system using a refrigeration manifold
When is a crankcase pressure regulator set up?
After defrost cycle has terminated and compressor has started
What pressure shall be used to calculate the superheat setting of the evaporator when a TXV is used as the metering device?
b. Evaporator outlet pressure near the sensing bulb
Defrost may be initiated by:
Time, temperature or pressure
Defrost may be terminated by:
Time, temperature or pressure
Calculate the total “u” factor of a freezer wall constructed of the following: 6” of polyurethane; having an “R” value of 6.25 per inch
8” concrete; having a “C” factor of 0.58 Btu/(hr)(ft2)(°F)
5/8” fire rated gypsum board; having a “u” factor of 3.2 Btu/(hr)(ft2)(°F).
.0253 Btu/(hr)(ft2)(°F).
What heat load value is unique when cooling fresh fruit and vegetables?
Heat of respiration
- The oil pump in a large semi hermetic compressor is located where?
on the crankshaft end
What type of TEV bulb charge is required on a large tonnage AC rooftop unit to reduce compressor overloading at startup under high load conditions?
Vapour charged
Off Cycle Defrost for a single circuit system, involves:
condensing unit off and evaporator fan on
Electric Defrost for a single circuit system, involves:
condensing unit off and evaporator fan off
Hot Gas Defrost for a multi circuit system, involves:
condensing unit on and evaporator fan off
Where is the Evaporator Pressure Regulator located
Outlet of the higher temperature evaporator
What type of oil used in stationary refrigeration and air conditioning systems will more readily absorb moisture when the container is opened?
Polyolester oil
walls of a building are 20’ high and 200’ long. The drywall has an R value of 0.5, the insulation is R10, the outside polystyrene board is R4 and the outside finish is R0.5. The indoor temperature is 72ºF and the outdoor design temp is -5ºF. Calculate the heat loss through the wall.
20,533 Btu/hr
a receiver is located in a location that may become colder than the evaporator
Thermostatically controlled heater elements are attached to the surface area of the receiver shell and shell is insulated
What is the effect on a system when the liquid line solenoid valve is installed backwards?
System won’t pump down
Where should the liquid line solenoid valve be installed?
. In the liquid line after the liquid line filter drier
What is the result when the TXV loses the charge in the sensing
Increase in evaporator superheat
Where should the TXV bulb be located for best sensing results?
. Evaporator outlet and placed to avoid effects of oil temperature
What is the correct mounting procedure of the thermostatic element bulb to ensure proper control of the TEV?
Clean evaporator outlet tubing after suction header, secure with similar metal clamp and insulate
- What is the purpose of the fan delay after a defrost cycle?
Allow moisture to drip off and the remainder to solidify on the coil
What is the term given to the device within the time clock that will cause the defrost cycle to end before its time
Defrost termination solenoid
What is the amount of sub cooling provided within a standard receiver?
0F
When will the king valve on a receiver be completely front seated?
When pumping refrigerant out of the liquid line
What happens to a reciprocating compressor when the suction service valve is completely front seated?
Compressor crankcase pressure should draw into a vacuum if the low pressure switch cut out is set low enough
The manifold gauge that shall be used to measure suction pressure is called
Compound guage
- What is the unit of measure for velocity?
Fpm
What two temperatures were measured by the electronic temperature control in the refrigeration lab
Box and coil
What type of input is used by the JCI MR4 and/or Omnistat for defrost termination?
Variable / analog
What switching action is used by a three-phase compressor j?
Tpst
What is the function of the low pressure switch used in the refrigeration lab to control the compressor
Recycling Pump down
What was the purpose of the delay on make timer in a recycling pump down control
Minimum off cycle for the compressor
What is the control voltage used in the refrigeration lab for the load switching components (relay and contactor)?
208vac
What voltage is required to power the Omni stat in this lab application
120vac
How many contactor poles were required for the single phase evaporator fan control in the low temp coil
2
What device is connected to the X & N terminal strip on the evaporator
Defrost termination thermostat
How many poles were required to disconnect the single phase defrost heater in the refrigerated box safely
2
How should all electrical loads be isolated when not in use for extended periods of time?
b. Tagged and locked out
Which is the pressure drop value of venturi and orifice type distributors
15 psi venturi and 25 to 35 psi orifice
Which TXV port design is intended for operation with floating head pressure
Balanced port
Under what condition would the refrigeration lab compressor lock out and not automatically restart
High pressure
Which force will close the compressor contactor?
Magnetic
What is illustrated by the pictorial electrical schematic
Location of electrical components
What is the function of a ladder electrical schematic
Sequence of operation
What is the purpose of the suction line trap at the base of a riser
Oil return
What is the term given to the device that held the pipe hanger to the beam
Beam clamp
Why was the electrical current draw higher on two of the lines feeding the compressor in the refrigeration lab
Single and three phase loads
- What tool(s) are required to set up a CRO?
Allen wrench, compound gauge & amp meter
Where is the refrigerant heat exchanger installed to improve sub cooling
Suction and Liquid
Which is the function of the suction /liquid heat exchanger in the refrigeration piping system
Sub cool refrigerant in liquid line
Superheat refrigerant in suction line
Increase NRE
The direct expansion shell and tube evaporator, water circuit can be cleaned by
Chemical cleaning
What happens to the refrigerant within the condenser
. De-superheated, condensed and sub cooled
Condensers must reject the heat from ____________when open drive compressors are used ?
Evaporator, suction line and compression
Which is the theoretical condenser ton for a reciprocating compressor
1.25 times evaporator ton
What is the result of increasing condenser pressure?
Higher pressure drops across TXV
. When an evaporator is installed 60 feet below the condenser what is the effect on the nominal tonnage of a TXV
b. Increase in nominal tonnage
What is the recommended maximum suction line temperature entering a compressor with a SST of 39 ° F
65° F
When the suction line is covered in ice it is an indication of
Suction line is below 32° F
What is the purpose of the suction line accumulator?
Protect compressor against refrigerant flood back
The result of installing a suction accumulator backwards is
Loss of oil in compressor
Insulating a suction accumulator will
Decrease the effectiveness of the accumulator when installed in a warm mechanical room
Accumulators return oil to the compressor by utilizing a
Venturi orifice
What type of float is found in an oil separator?
. High side float
Insulating an oil separator is required when
When a heat tape is used around the separator to prevent off cycle migration in a low ambient condition
What is the result of the float failing because of a leak, in an oil separator?
Compressor will eventually shut off on oil failure
To protect the compressor from off cycle migration what component(s) can be included in the design when low ambient conditions are a factor
a. Crankcase heater
b. Solenoid valve in the oil return line from the oil separator
c. a&b
What two pressures are sensed by the OPFC?
Compressor sump and oil pump discharge
The OPFC pressure differential is measured in units of
psi
What is the function of the “L & M” terminals found on a OPFC?
Control circuit for compressor
When using an ohm meter to check a conventional oil pressure failure control between the 240 and 120 terminal what is the expected value, if the control is new?
1000 Ω
When using an ohm meter to check a conventional oil pressure failure control between the L and M terminal what is the expected value if the control is new?
0Ω
When using an ohm meter to check a conventional oil pressure failure control between the 240 and 2 terminal what is the expected value of a new control?
> 1000 Ω
control action of the condenser fan cycling control is
Reverse acting
What is the most correct melting temperature of B Cup 15 as per ANSI
> 1100 ° F
. When a combination dual pressure control having manual reset is installed, the low side pressure switch is used as a/an
. Depends on application in control sequence
What are three pressures used to control superheat in an
Evaporator, spring, & bulb
What are the two basic valve designs used in a reciprocation compressor
. Ring and reed
. Comfort cooling systems which use hot gas bypass to the evaporator inlet require the use of an __________ when installed with an orifice plate distributor a.
. Auxiliary side connector T
Compressors that use a method of ___________for capacity control are more energy efficient than a compressor that use another form of capacity control
Suction valve lifting or suction cut off
What procedure is used to verify rotation, prior to startup, of a 3 phase compressor?
use a phase sequence indicator on the line side of the starter
The thrust bearing is used to absorb the________ energy exerted by the crankshafT
Parallel
Paul’s signature saying
Does that make sense
The windings of a semi-hermetic motor are located in the
Stator
The windings of an open drive compressor drive motor are cooled by
Ambient air
The coil of a normally closed lock out relay is wired
in parallel with the safeties and in series with the load relay
The tool used to verify the winding insulation is the
Meg-ohm meter
The capacitor in a PSC causes a ______angle shift between the voltage and current
Phase
. What is the effect on a refrigeration system if the compressor is oversized for the application
Low suction pressure
What is the effect on the refrigeration system if the TXV is undersized
High super heat
What is the purpose of the external equalizer port on a TXV
. Compensate for high evaporator pressure drop
What is unique about the relay used in a NC lock out circuit
High impedance
A 24 VAC control circuit utilizes the N/C LOR strategy and the system has locked out on high pressure the voltage drop across the coil of the LOR relay is
approximately_____________
20 VAC
When the N/O LOR contacts are not used in a N/C LOR circuit the LOR can be reset by _____________________
All of the above
What is the purpose of a recycling pump down circuit
Minimize off cycle migration
What is the purpose of a non recycling pump down circuit
Prevent short cycling of the compressor
What device is controlled by the “3” terminal on a defrost time clock
Defrost heater
What device is controlled by the “4” terminal on a defrost time clock?
Compressor contactor
What device is connected to the “1” terminal and the “3” terminal on a defrost time clock
Defrost heater
And Time clock motor
What term describes the switching action of the time clock contacts when the defrost heater and compressor control circuit are the same voltage?
Spdt
What device is connected between the “1” terminal and the “N” terminal on a time clock?
Time clock motor
What device can be connected to the “N&X” terminals on a defrost time clock?
Low pressure control
Is the Omni stat a time of day timer (TOD) or a cycle timer?
. Cycle timer
Which statement is correct regarding the vacuum pump
The gas ballast is turned counterclockwise one turn prior to start up and then clockwise 1 turn at 3,000 µm
The temperature range for a defrost termination and fan delay “klixon” is ____.
55 º F and 25 º F
What type of relay switching action is available on the A 419 temperature control
Spdt
What is the switching action of the relay required for the non recycling pump down control that provides a holding circuit and separate contacts for the compressor circuit?
Dpdt
When would two low pressure switches be used on a refrigeration system
Operator and safety switch
The NO lock circuit normally requires a _______ to start the equipment
Momentary contact
Scr are found in what
Soft start
~>|~ what side is anode and what side is cathode on diode
Left is anode right is cathode
When an air cooled condenser is utilizing “condenser flooding” refrigeration pressure regulators to maintain head pressure what component is also required?
Receiver
Condenser flooding is accomplished using the following components
ORI, ORD and receiver
ORI regulators used in condenser flooding applications are similar in operation to the _______________ regulator.
Evaporator pressure
The ORD regulator opens on a differential in pressure between the ________ & ________
Compressor and receiver
Condenser flooding may require condenser fan control through the use of
Temperature controls
And Pressure Controls
And VFD
Sensible cooling of air is calculated by the following
Q = CFM x 1.08 x ΔT
Evaporator approach is the difference between the
. Leaving air or water temperature and SST
Total air cooling load can be calculated by the following
Q = CFM x 4.50 x Δh
If a suction line is 7/8” or smaller, the sensing bulb is generally located:
at the 12 o’clock position
What procedure is required in order to reduce evacuation pull down time?
increased hose size and increase space temperature
Insulation on piping is used to:
Prevent refrigerant from picking up sensible heat
Which method is used to prevent oxidation within piping during brazing
purge with near inert gas
How much cooling is required to turn 10 pounds of steam at 214°F in to ice at 30°F
12,960 Btu’s
What is the spring pressure setting of a TXV having the following conditions? R-22, SST = 40º F, Evaporator outlet temperature is 52º F
19 psi
If a unit cooler had 4 fans rated at 250 watts, how many Btu’s of heat energy would there be?
3413 btu’s
The EPR valve is:
located after the evaporator to prevent the evaporator pressure from decreasing below set point
The amount of slope in a 40 ft. horizontal refrigerant vapour line should be:
2”
A 100 ton system maintains a 40°F SST. The enthalpy of the refrigerant entering the evaporator is 50 Btu/lb and the enthalpy entering the suction line is 110 Btu/lb. How many pounds of refrigerant are circulated?
333 lb/min
The CPR valve is:
located before the compressor to prevent overloading
What is the test pressure used on a refrigeration system component when performing a pneumatic pressure test?
At 110% component design pressure
Which family of refrigerants would be considered azeotropes?
R-500
An R-134a system has a TEV with a spring pressure of 9.5 psi, an evaporator pressure of 30.5 psig. Calculate the superheat?
10°F
The entrance door frame of a walk-in freezer requires:
a heater
Which method of starting provides the highest starting torque?
Across the Line
What is the voltage unbalance for the following?
L1 – L2 = 197 volts, L1 – L3 = 208 volts, L2 – L3 = 201 volts
3%
. What are the terminal connections for a dual voltage motor wired in low voltage, Part Winding Start?
1MC T1 – T1, 1MC T2 – T2, 1MC T3 – T3, 2MC T7 – T7, 2MC T8 – T8, 2MC T9 – T9
What is the sequence for a wye delta start, closed transition?
S in, 1M in, 1A in, S out, 2M in, 1A out
What are the terminal connections for a dual voltage motor wired in high voltage delta
1MC T1 – T1 – T12, 1MC T2 – T2 – T10, 1MC T3 – T3 – T11, T4 – T7, T5 – T8, T6 – T9
