Automatic expansion valves work with
Evaporator pressure closes valve spring pressure opens valve
A faulty check in a pump will cause the most damage on
Startup
If the T E V's sensing bulb falls off the suction line you will
Flood the evaporator
A clogged condenser pump strainer can cause a loss of pressure causing
High condenser head pressure
A solenoid valve is part of the pump down cycle
Thermostat solenoid valve and then the low pressure control
What is proper start up procedure?
Start chiller water pump, start condenser water pump,check tower fans, check compressor oil, check position of refrigeration valves, start machine.
A reciprocating machine cycles multistage compressors on and off with the
Low pressure control
The refrigerant that has the best refrigerant effect is
Ammonia
In an induced draft cooling tower that is operating efficiently the leaving water temp is at
Some temp between the prevailing dry and wet bulb temp
A sudden reduction in the supply of condenser water could result in
An open valve
Reciprocating compressor unloaders work by
Keeping compression suction valve open
In a well designed system the percent of lubricant circulated should not exceed
10%
Oil foaming in the compressor is a result of
Liquid refrigerant in the crankcase
The main reason for installing a oil separator on the discharge line is to
Return oil back to the compressor crankcase
In a reciprocating compressor using the splash system for lubrication the domain of oil is caused by a
Sudden decrease in pressure
Charge vapor into the
Suction side of the compressor (low side)
Oil in a refrigerant system reduces
Wear and friction
A filter drier is used to
Remove moister
Oil separator is located on the discharge line as
Far from the compressor as possible
A solenoid valve
Does not vary the flow of refrigerant
The T E V
Modulates and controls the flow of refrigerant into the evaporator
If you use an automatic expansion valve with a variable load you will
Starve the evaporator
A motor has 4 belts if one is worn replace
All the belts
Non condensable gases can cause
High head pressure
Horse power will
Increase as the head pressure increases
Horse power will
Decrease as the head pressure decreases
Superheated vapor is defined as a
Dry vapor
A sling psychrometer is used to measure
Relative humidity
An automatic expansion valve maintains a
Constant evaporator pressure
If the evaporator doesn't respond to adjustments of the T E V it may be due
To oil logged on the low side
When using a bribe solution in a system us
Di-chromate tablets to prevent rusting
If a halide torch turns yellow it is caused by
A clogged sample tube
The pressure of having 2 compressors in a cascade system is to operate at
Very low temperatures
A pressure relief valve is better than a fusible plug because a
Fusible plug can not reseat
Compressor knocking could be caused by
Refrigerant slugging in the compressor
If the TEV's spring was to break it would
Flood the evaporator and raise suction pressure
The T E V of equalizer line makes up for the
Pressure drop in the evaporator
When installing pipe and you need a 90 degree elbow use a
Factory made 90 degree elbow and braze it in
A service valve stem cap protects the valve from being
Inadvertently turned from its position and from being damaged
Semi hermetic compressors have the advantage over hermetic compressors because
They can be serviced on site
When using a portable compressor recovery unit to remove vapor the
Vapor density is decreased
The amount of pressure that flows through the orifice plates is determined by the
Difference in pressure between the high and low size
If you were running three compressors the state of refrigerant leaving the third compressor is a
Superheated vapor
A T E V restricts the amount of refrigerant from the
High side to the low side
A halid torch burns from
Blue to dark blue or purple when a week is detected
The main reason for a crankcase breather line is to prevent
Oil from slugging in the compressor
The middle port on a manifold gauges is connected to the
Recovery cylinder or the charging cylinder
A forced draft cooling tower is better then a natural draft because it is
Smaller and not affected by prevailing winds
The proper way to start a pump is to
Open the suction valve and close the discharge valve start the pump and then slowly throttle open the discharge valve (seasonal start up)
Fusible plug setting is
280�
The flashpoint of compressor lube oil is
Higher than the compressor temperature
Heat removed from the refrigerator in the condenser is
Sensible and latent heat
A compressor safety head is a
Valve plate help down by a heavy spring
A centrifugal machine is characterized by
High volume and low pressure
If condenser pressure is high and another pump has to be turned on you would have the
Suction valve completely opened and discharge valve open to a throttled position
If you disconnect the external equalizer on a T E V you would
Flood the evaporator
You achieve capacity control on a reciprocating compressor by
Opening suction valves by using some form of control
The ratio of actual water vapor in the atmosphere to the saturation pressure is called
Relative humidity
The most accurate statement regarding compressor motors that run in a refrigerant atmosphere is that they use
Material tailored to the refrigerant
MUNTZ
Material should not be used with ammonia
Venting a manifold or purge line is prohibited with any
Refrigerant containing chlorine. (HCFC CFC)
You would not use a solenoid valve to
Vary the flow of refrigerant
The muffler is located between the
Compressor in the condenser
Refrigerant affect is always lower than latent heat because
Heat required to cool the refrigerant from compressor discharge to evaporator temperature is subtracted from the latent heat
You use a T E V with an external equalizer when there is more than
2.5 pressure drop through the evaporator coil
Direct systems
Are most likely to week refrigerant into building spaces
Gauges on the high side should be graduated to
At least 1.2 times the design pressure
When brazing in a class T machine room you must in sure the flame is
Enclosed invented to open air
In an emergency you can dump refrigerant under
FDNY supervision
An R-22 system's head pressure with a condenser water supply temperature of 85� is
200-215 p s I g
When you run two pumps in parallel you
Increase total flow rate (GPM) Pressure is the same when running one or two pumps
A refrigerant cylinder can only be filled
75% NYC (a 40 gallon can be filled with 30 gallons)
Calcium chloride sodium chloride and glycol
Are used as chilled water Brines in an indirect system (R-22 is not a brine)
Failure to maintain water temperature of condenser water can result in
High head pressure
Frost on suction line and compressor could be caused by the
T E V being open to wide
If cooling tower is not chemically treated you could cause
Bacteria growth and rusty pipes
The low pressure control
Cycles the compressor on and off
If there is a refrigerant leak the operator should be aware of
Toxicity and oxygen deprivation capabilities of the refrigerant
All group one refrigerants
Require an oxygen deprivation sensor (R-11 R-12, R-22, R-134A)
A low head pressure chiller's ruptured disc is set at
15 p s I
An automatic purge unit is required for systems that operate
Below atmospheric pressure (in a vacuum)
High head pressure and temperature could be caused by
Dirty condensable tubes
If wetbulb temperature decreases it can
Lower the temperature of the cooling tower
Use a three-way valve (service valve)
To isolate the pressure relief valve while keeping the system and service
Charge with the vapor first so you don't
Freeze the evaporator tubes (centripetal machines)
Clogged eliminator fins on a cooling tower could lead to a
Higher condenser supply water temperature
Orifice plates serve as metering devices in centrifugal compresses the vessel they are contained in can also serve as an
Economizer
A jet ejector if restricted will have
Insufficient had to lift the oil (back to the oil sump)
The low side gauge (saturation pressure) can be used to
Estimate to leaving chilled water temperature
Water tube leaks in a low-pressure chiller can be found with
Hydrostatic tube test
R-11 and R-123 refrigerant are
Oxygen depleted, heavier than air and class one and class two substances
A centrifugal chiller purge unit
First takes a combination of air and refrigerant from the top of the condenser then removes air and noncondensible and finally returns liquid refrigerant back to the evaporator
Electric resistant heaters (resister circuit)
Can be used to defrost evaporators
Refrigerant enters the condenser as a
High-pressure gas and leaves as a high-pressure liquid
When using warm water to increase the release the rate of R-12 do not exceed a water temperature of
90�
R-11 water oil at 70� and at atmospheric pressure would settle in a container from top to bottom in this order
Oil on top then water and R-11 on the bottom
You can achieve capacity control on a reciprocating compressor by
Opening suction valves using some form of control (unloaders)
Power consumption from an induction motor is measured in watts using the formula
Volts times amps times power factor
Low condensing pressure is not good because
Expansion valves will not be fed properly
And in-line refrigerant cleaning system (into cleaner) is advisable because
Refrigerant reacts with lube oil
If a condenser water pump is cavitating this problem could be caused by
A faulty water level control
Capacitors our devices which have the ability to
Store electricity and are used to start motors
The refrigerant with the highs latent heat is
Ammonia
Transformers
Areelectric devices which change the value of AC voltage to another AC voltage (step up or step down voltage)
The most common metering device used on reciprocating commercial systems under 3 tons is the
Thermostatic expansion valve (also used over 3 tons)
The maximum pressure used to leak test low-pressure chillers is
10 P S I G
Under the EPA regulations you can pressurize the system for a
Non-major repair with nitrogen and a trace of R22
Under EPA regulations replacement of an
Evaporator coil is always considered a major repair
R11 at 14.7 p s I a (0 p s I g) will boil at approximately
74.5�
When you remove valve plates you should replace
The valve plate and the valves
If an electric motor has its windings reduced by one half and all other factors remain equal the power developed by the motor is
Decrease by one half
If a system is excessively cycling crank case temperature is high, discharge is low, and suction is high this could be caused by
Faulty compressor valves
Centrifugal compressors can control capacity with
Variable inlet guide veins
Centrifugal compressors can control capacity with
Variable speed motors
On a reciprocating compressor there are stop valves on the
Inlet (suction side) and the outlet (discharge side)
To prevent freezing water coils of a low-pressure chiller you should first
Charge as a vapor; circulate water, do not charge liquid until the saturation temperature is above 38�
Refrigerant is added to a low-pressure centrifugal chiller through the
Evaporator charging valve
You can store anextra 20% of refrigerant charge up to a maximum of
300 pounds on site
Before a low-pressure appliance is dismantled and salvaged
Refrigerate must be recovered
Compound gauges measure
Positive pressure and negative pressure (vacuum)
Oil traps or oil separators return or oil back to the
Compress crankcase
If a motor goes off on overload you could check it's amperage with an
Ammeter
You can check a short in a compressor motor with an
Ohmmeter
If you pump down a compressor to 25" HG then stop the compressor. If the pressure then increases you could have
Faulty compressor valves
The pressure a centrifugal compressor can develop depends on the
Top speed of the impala
If the external equalizer was to break you would lose
The entire charge
Oil pressure should be at least
15 to 30 p s I g above the suction pressure in a reciprocating compressor
Shell and coil condensers are not mechanically serviceable and must be cleaned
Chemically
Shell and tube condensers can be
Mechanically clean with brushes
To minimize pressure drop
Avoid using a globe valve
A condenser pump in the basement has 120 p s I g at the inlet from the basement to the roof cooling tower the height of water is 277 feet what is the formula
2.3 1 times 120 = 277 .2
Glycol is better than brine because it
Eliminates corrosion problems
Water regulating valves work off of
Condenser head pressure
Refrigerate enters the compressor as a
Low-pressure superheated vapor and leaves as a high-pressure superheated vapor
Suction pressure increases
The refrigerant affect per ton decreases
T E V sensing bulb is attached on the suction line at the
End of the evaporator
Outdoor cooling towers have this to prevent freezing
Heating coils
The low side flow controls the
Low refrigerant into the evaporator
In a refrigeration system the heat absorbed in the evaporator is later rejected in the cooling tower using the process of
Evaporation
An older type of cylinder unloader is designed to control
Cylinder clearance pockets
A fast way to check gauge pressure reading in the field is to
Open it to atmospheric pressure it should read 0 p s I g
If the suction pressure is 62 p s I g and discharge pressure is 110 p s I g the compression ratio is 1.6 the formula is
Discharge pressure p s I a divided by the suction pressure p s I a (add 14.7 to convert psig to psia ) 124.7�76.7
If a unit using a low side float was short cycling it could need
Additional refrigerant to be charged
If a hot wire is touching the inside of the motor casing a R M O could get an
Electric shock if touched
If a centrifugal pump is running fine at full discharge but if throttled it loses flow
A clogged strainer could be the cause
A fusible plug would not be used in a system that
Does not have any heat
A Compressor stuffing box prevents the
Leaking of refrigerant vapor
The A E V works on two pressures
Evaporator pressure is closing force and spring pressure is the opening force
If you overcharge the system you will run with
High head pressure
An evaporative condenser uses both
Air and water
Silver solder
Is used to connect to pipes together when brazing
If there is a 5 pound pressure drop in the evaporator the external equalizer line will supply a
Closing pressure to the T E V from the same point the temperature of the sensing bulb is taken
Copper piping is used in refrigerant because it is
Good conductor for heat transfer
High-pressure vapor is found
Above the compressors valve plate
Low-pressure vapor is found
Below the compressors valve plate
Oil collected in the oil separator is generally returned
Back to the compressor crank case
Automatic water regulating valve is very water flow according to
Condenser head pressure
If they are R M O needs to vary flow of refrigerant in a system where the continuous variation in flow
Does not include the solenoid valve
If high superheat appears in the suction line this could indicate you are
Low on refrigerant
You would not use a fusible plug on a system with no temperature because it releases on
High temperature only and not on high-pressure
If the compressor failed to start and you already checked the electric circuits motors, switches, and breakers the problem could be a
Faulty pressure temperature control (low pressure controller)
The advantages of an A E V is it
Maintains a constant evaporator pressure, it's a simple design and little could go wrong, and an excessive charge will have no effect
You find stop valves (service valves) on the
Inlet of the compressor and the discharge of the compressor and on the outlet of the condenser or receiver
The T E V drops refrigerant from a high-pressure liquid to a low-pressure liquid it also
Maintains a constant superheat in the evaporator
You would use copper and aluminum tubes because of their
Thermal characteristics for transferring heat
Imprinted on the fusible plug is the
Temperature at which it melts
If a machine with a R - 123 had a leak the
Refrigerant monitor would go off
When a purge unit is running the
Compressor must also be running
Another disadvantage of the A E V besides not responding well to various loads is that it
Does not work well with more than one evaporator in the system
The solenoid valve has a magnetic coil that
When energize will lift a plunger off the seat (normally closed valve)
Liquid line solenoid valves are sized according to
Refrigerant tonnage and a pressure dropped to the valve that is acceptable
Low pressure chillers should not be pressurized above
10 psig or you could blow the rupture disc
Pressure relief devices discharge point must be
15 feet above the ground and must be 20 feet or more from any window vent opening or building exit
If city water is too expensive if available water from
Well, rivers, lakes, or the ocean may be used
Fusible plugs give no protection against
Excessive pressure developed by other means than heat
The refrigerator inside the T E V's sensing bulb is known as the charge for the T E V. There are four types of charges that could come with the T E V. They are
Liquid charge bulb - cross liquid charge - vapor charge bulb - cross vapor charge bulb
Liquid cross charge and vapor cross charge have
A different charge in sensing bulb then the system charge
The restriction caused by filter dryer in the suction line can cause
More reduction in capacity then a filter dryer in the liquid line
Air, nitrogen, and other noncondensible gases collect in the
Condenser
Activated ammonia, silica gel, and drierite
Are frequently used as desiccants in filter driers
Ammonia system sight glasses are the liquid glass type and have
Automatic check valves and manual had valve in each line to the glass
Wearing rings prevent discharge water from leaking back into the suction I of the impeller this leakage could cause
Damage to the impeller and the pump casing
Flare connections are not used on copper tubing larger than three quarters of an inch. It is
Too hard to tighten sufficiently to make a gas tight joint in larger sizes
Compression valves are located on
Both sides of the valve plate discharge on top and suction below
In the winter air cooled condenser's can be controlled by
Cycling fans - variable speed motors or damper controls
The water regulating valve opens or closes automatically in response to the condensing pressure and
Maintains the set or desired condensing pressure
Cooling towers require chemicals to
Reduce the formation of scale and algae
When testing a three-phase circuit with the clamp on type Ammeter
Check each phase individually
A centrifugal pump is fully primed when it is
Full of liquid and all the air has been removed
A strong wind could cause
A problem when using a halide torch on the roof
Synchronous motors run with a
Leading field current
The amount of ventilation for refrigerant removal purposes should be determined by the refrigerant content of the
Largest system in the machinery room
Each fusible plug must be marked with the
Melting temperature of the alloy
Recovery cylinders are
Gray with yellow tops
A low refrigerant charge will
Starve of the evaporator
The petcock on a pump is used to
Bleed air from the pump
Filter driers use a
Desiccant to remove moisture
Superheat
Dry vapor above its boiling point
A efficient condenser runs with
A low condenser pressure
The order of devices in the liquid line is as follows:
King valve, filter drier, solenoid valve, sight glass, T E V