A suction line should be ____ to prevent moisture in the air from condensing on the cold tubing.

Refrigeration is the process of ___ the air in a defined space.

lowering the temperature of

The temperature of a material decreases if the material ____ and nothing else happens that would have the opposite effect.

contacts a cooler material

The two kinds of air conditioning are

One of the physical states of matter is

You can cause matter to change its physical state by

Thermal energy that cannot be detected by a thermometer is called latent heat. Thermal energy that is directly related to the temperature of a material is called ___ heat.

A temperature of 45 degrees F is about the same as ___ degrees C.

Heat can be transferred from one place to another by the process of

The latent heat of vaporization of a substance is the amount of heat the substance absorbs as it

A refrigeration system has been turned off for several days. It contains both liquid refrigerant and vapor. Suddenly a line containing the refrigerant breaks; what happens inside the system?

From the compressor, refrigerant flows to the

The graph below is the pressure-temperature chart for a refrigerant. Point ___ represents a condition of superheating.

Compared to a dry-expansion evaporator, a flooded evaporator of the same size

The purpose of a cooling medium is to

remove heat from compressed refrigerant vapor

An automatic expansion valve is a metering device that maintains a constant pressure in the

The properties of air that are important in psychrometrics include

In a sling psychrometer, the wet-bulb temperature is usually a lower value. If the difference is very small, you know the air is quite

Air that is saturated is air that is at the

Relative humidity changes if the ___ changes, but the specific humidity does not.

To calculate the enthalpy of a sample of air, you must include

latent heat of the water vapor

In order to remove the moisture that enters a refrigeration system during repair, you must evacuate the system by using a ___ to make all the moisture vaporize.

One useful method of detecting leaks in a refrigeration system involves using an ____ leak detector.

Relative humidity can be measured with an

Which of the following is a correct match between an electrical value and the instrument used to measure it?

In the list below, identify the line that correctly matches one of the classes of work-area hazards to an example of that class of hazard.

Chemical; container of refrigerant

If you increase the pressure of a liquid, its ___ temperature will ____, meaning that it will boil at a higher temperature.

At a temperature of 30 degrees F, the enthalpy of the saturated liquid refrigerant is 3.5 BTU/lb. The enthalpy of evaporation is 87.4 BTU/lb. What is the enthalpy of the saturated vapor?

In the following diagram of a refrigeration cycle, the line between points ___ represents the amount of subcooling

A system must provide 8 tons of refrigeration. What compressor horsepower is needed for this system?

Liquid refrigerant can be sub cooled by transferring heat either to the atmosphere in the condenser or to the ____ in the suction line heat exchanger.

An "ideal refrigerant" has which of the following characteristics?

In the ASHRAE standard designations of refrigerants, the

letter R is being replaced by letters identifying the chemical structure.

Temperature glide occurs only in ___ refrigerants.

ASHRAE classifies refrigerants according to how hazardous they are. The ratings are based on flammability and toxicity of the refrigerants. The most hazardous refrigerants are rated

When handling and storing refrigerants, you must protect yourself by

The ozone layer in the earth's atmosphere is important because it

absorbs ultraviolet radiation from the sun

CFCs released into the atmosphere deplete the ozone layer by breaking apart and releasing chlorine ions that then remove single oxygen atoms from the ozone molecules. CFCs also contribute to the greenhouse effect by

absorbing infrared radiation

In order to minimize the release of CFCs into the atmosphere, refrigeration service technicians must

recycle refrigerants on-site, if possible

A recycled refrigerant may be placed in

the system from which it was removed

During the installation of a new system, the chance of future refrigerant leaks can be reduced by

installing a muffler in the compressor discharge line

To reduce the depletion of the ozone layer, the U.S. government has implemented laws requiring the

testing and certification of all technicians whose work can cause the release of harmful refrigerants

The EPAs final rule concerning the handling of refrigerants and refrigeration equipment requires

certifying the equipment used in recycling and reclaiming refrigerants

The compressor for an active recovery system is part of the ____. The compressor for a passive system is part of the ___.

recovery equipment; system being serviced

Which of the following is required by the EPA

Certification activity report

Technicians who work on residential air conditioning systems must have at least _____ certification.

Which of the following is a contaminant that can be removed by a filter-drier?

An absorption type desiccant holds water by means of a ___ action, but an adsorption type desiccant holds water by means of a ___ action.

If you mount a filter-drier in a vertical suction line, the inlet should be located at the top so that ___ cannot become trapped inside.

When selecting a filter-drier, you need to base your selection in part on the

minimum particle size it can trap

When installing a filter-drier in a refrigeration system, you should

You can pinpoint leaks in a new refrigeration system by charging the system with ___ and using a ___

When preparing to use a gauge manifold in servicing a pressurized refrigeration system, you connect its high-side charging hose to the

compressor discharge service valve

To check the charge in a refrigerant system, you can look at the ___ in the liquid line. If the charge is low, you will probably see ___.

In using the deep-vacuum method of dehydrating a refrigeration system, you lower the pressure to about ___ microns or less. With the vacuum pump turned off, a gradual rise in pressure tells you the system is ___.

You can tell whether you have charged a refrigeration system with the correct amount of refrigerant by checking the

weight of refrigerant used

The miscibility of the refrigerant oil is its ability to

Oil that becomes mixed with the refrigerant in a system can cause which of the following problems?

An oil separator is located between the ____ an ___ in order to keep oil out of the condenser and evaporator.

Moisture in a refrigeration system causes a variety of problems, including

blockage in cold parts of the system

Before you check the oil level in the sight-glass on a refrigeration compressor, you should stop the compressor for at least ____. The compressor should be ____ while you check the oil level.

A positive-displacement compressor uses a piston or other device to

compress refrigerant vapor in a chamber

Which of the following is a kind of kinetic displacement compressor?

Which of the following is part of a scroll compressor?

A multiple stage refrigerant system has more than one

When selecting a replacement compressor, you need to make the replacement will operate (with/at) the proper

Among reciprocating compressors, the crankshaft is usually vertical in a ___ compressor, but horizontal in an ____ compressor

On the pistons of reciprocating compressors, the ___ ring(s) prevent oil from reaching the compression chamber. The ___ ring(s) prevent refrigerant from escaping around the piston during compression.

Which of the following is a method of distributing lubricating oil in a reciprocating compressor?

A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to flow through the ___ port during the ___ stroke.

One way of reducing vibration problems in reciprocating compressors involves the use of

One advantage of rotary compressors over reciprocating compressors is that the

Slugging is the entry of ___ refrigerant into a compressor. Cavitation is the formation and collapse of ____ in a liquid flowing under pressure.

One purpose of the accumulator on a rotary compressor is to

keep dirt and debris out of the compressor

Helical compressors differ from rotary compressors in that they have

In a scroll compressor, one scroll is stationary and the other ____. Refrigerant enters the scrolls at the ___ and leaves at the center.

The amount of compression in a centrifugal compressor depends on the ____ the impeller, which depends in turn on the impeller's ___ and rate of rotation

In reverse hydrostatic sealing, the flow of ___ across the seal opposes the flow of ____ across the bearing.

Which of the following motors can be used in hermetic compressors?

Capacitor start, induction-run

You can reverse the direction of a single-phase induction motor by

reversing the connection of either the starting or the running winding

To change a dual-voltage motor to run on 240 V instead of 120 V, you need to

connect the two running windings in series

A single-phase motor used in a hermetic compressor has a relay to disconnect the starting winding from the circuit when the motor approaches its running speed. One kind of relay operates when the current in the ___ winding falls to a preset value. Another kind operates when the voltage across the ___ winding rises to a preset value.

Two basic categories of motor starting devices are

A reduced-voltage starter limits the current to the motor at startup in order to prevent

voltage drops to other equipment

Overload protection for compressor motors may be provided by an

Crankcase heaters are especially useful on compressors that are subjected to

Installing a suction-line accumulator can protect a compressor from damage caused by

The "first rule" of preventive maintenance for compressors and related components is to

follow the manufacturer's recommended maintenance schedules and procedures

Typical preventive maintenance procedures for compressors and related equipment include

listening for unusual noises

A compressor may overheat because of a

When pumping down a compressor for service, run the compressor with the valve on the suction line closed, then close the valve on the discharge line and stop the compressor. Repeat this process until the pressure holds at ___ psig.

After disassembling a reciprocating compressor and cleaning the parts, you should inspect the parts for

excessive wear on the bearing surfaces

The capacity of a condenser is affected by the

area of contact with the cooling medium

Natural-draft air cooled condensers and forced air condensers are alike in that both types

need 600 to 1200 cfm of air per ton of capacity

Low-ambient control in an air cooled condenser can be achieved by

Spring loaded relief valves protect a system against explosion by acting in response to high ___. Fusible plugs act in response to high ___.

Periodic maintenance of air cooled condensers includes doing which of the following every three months?

checking all belts and pulleys

In the ___ system, water passes through the condenser to cool the refrigerant. The water is then ___.

wastewater; discharged to the sewer

In a water cooled condenser system, "makeup water" is used for

replacing water lost through evaporation

Tube-in-tube, shell-and-coil, and shell-and-tube condensers are alike in the following way

liquid refrigerant collects at the bottom

A condenser has a pressure-relief device that ___ if the refrigerant pressure becomes too high.

Generally, how long should you allow a chemical cleaner to stand in a condenser

Which of the following can increase the capacity of a cooling tower or a spray pond by the greatest amount?

decrease in dry-bulb temperature of the air

What type of cooling tower is shown in the drawing below?

induced draft, counter flow

Which components in the water-circulating system for a cooling tower or spray pond are used to keep the concentration of minerals low?

The capacity of a cooling tower can be controlled by means of a

As part of maintaining a cooling tower, you should check the ___ everyday.

The basic classifications of evaporative condensers are

blow through and draw through

An evaporative condenser may include a de-superheating coil for the purpose of

reducing the formation of scale

Which of the following methods will maintain condensing pressure during cold weather operation?

circulating water intermittently

What will prevent the water in an evaporative condenser from freezing during cold weather?

As part of maintaining an evaporative condenser, you should check the ___ every three months.

pulleys and belts for wear

One of the main categories of water related problems in an air conditioning or refrigeration system is

Corrosion in a water cooled system can be caused by

Scale formation can be reduced in a refrigeration system by adding ___ to the cooling water.

Bacteria and algae can be controlled in a refrigeration system by adding ___ to the cooling water.

Chemical deterioration in a wooden cooling tower can be controlled by

keeping pH of circulating water in the 6.0 to 7.5 range

In a cooling system, one of the main lines in the piping system is the ___ line.

Steel pipe is typically joined by means of

Tubing is often preferred over piping in a cooling system because it

Refrigeration tubing is typically joined by

When brazing tubing to a fitting, you should first heat the ___ until the ___ melts.

The function of the discharge line in a refrigeration system is to

convey the refrigerant to the condenser

The "entrainment" of compressor oil is the ___ the moving refrigerant

drawing and transporting of oil with

In order to keep entrained oil droplets moving through the piping, the refrigerant must move at ___ fpm in horizontal piping and ___ fpm in a vertical riser.

500 to 700; 750; to 1,500

Refrigerant can be prevented from collecting in the compressor during the off-cycle by installing a ____ in the ___.

check valve; discharge line

Accessories often added to a discharge line include a

Sub-cooling is desirable in the liquid line, because it

reduces the volatility of the refrigerant

If the pressure in the liquid drops, flash gas can form, which can reduce the

With halocarbon refrigerants, the movement of oil is better in the liquid line than in the discharge line, because the

oil is miscible in most liquid refrigerants

A liquid receiver is used to

store all the refrigerant during repairs

The purpose of a solenoid valve in the liquid line is to stop the flow of refrigeration to the

A double suction riser installed in a cooling system enables the system to operate at maximum load without creating excessive ___ in the suction line.

An accumulator in the suction line traps oil and liquid refrigerant to keep it from entering the ___. A heater in the accumulator evaporates the ___.

An evaporator-pressure regulator valve closes part way if the pressure at the evaporator outlet becomes too ___. A crankcase-pressure regulator valve closes part way if the pressure at the compressor inlet becomes too ___.

The suction line is insulated in order to prevent or reduce ___ the line.

condensation on the outside of

The amount of oil that can build up in the suction line of an idle single-compressor system is much ___ than the amount that can build up in an idle compressor of a multiple compressor system. To prevent damage from excessive oil buildup, the suction line should include a trap with a minimum rise of ___ in.

Piping problems that result in operating problems are often caused by

Which of the following expansion joints can be used in a refrigerant line?

Which kind of support is appropriate for a horizontal piping run 15 feet long?

The problems caused by vibration in the piping of a cooling system include

damage to valves and controls

Insulation is needed on the liquid line if the line is ___ than its surroundings. The purpose of insulation on the liquid line is to prevent the loss of any ___ of the refrigerant.

What is the main function of a control system?

maintain a variable at a setpoint

What are the basic components of a control system?

Sensor, controller, controlled device

Air-conditioning and refrigeration systems are commonly controlled by ___ control.

Which of these control loops adjusts the setpoint automatically?

The power to operate a control system may come from

An RTD responds to a change in temperature by undergoing a change in its

Relative humidity is defined as the amount of moisture in the air

divided by the amount it can hold

In a pressure sensor that uses a Bourdon tube, changes in pressure are sensed by changes in the ___ of the tube.

position of the sealed end

An air-conditioning system has a two-position damper in the duct bringing outside air into the building and a second two-position damper in the return-air duct. When the system shuts down, the outside-air damper should be ___ and the return-air damper should be ___.

Which of the following is an advantage of variable-speed drives over older methods of controlling output of an air-conditioning or refrigeration system?

Proportional control can be used

Unlike floating control, proportional control is

The air supply for a pneumatic control system requires which of the following

A PE relay is used to control a device operated by

Setting the gain of a controller determines how much a change in the ___ affects the ___.

controlled variable; controlled device

Adding integral action to a controller improves system performance by reducing ___. Adding derivative action improves performance by reducing ___.

offset; overshoot and undershoot

In pumpdown control, the compressor starts when the pressure ___ in the ___.

The high-pressure control in the discharge line of an air-conditioning or refrigeration system responds to high pressure by

shutting down the compressor

A differential-pressure oil-safety control shuts off the compressor if the difference in pressure between the ___ and the oil pump ___ does not become high enough within a given time.

compressor crankcase; discharge

What kind of capacity control is commonly used on large reciprocating compressors?

In modulating the flow of water to hydronic terminals, the temperature control method has the advantage of

preventing system freeze-up in cold weather

In setting up a preventive maintenance (PM) program, your first step should be to

inspect the system in detail

To maintain oil pressure in a 10-hp reciprocating compressor, a ___ oil pump is used.

To adjust the water-regulating valve on a water-cooled condenser, you should turn the adjusting screw until the ___ is at the design value. You should make this adjustment when the equipment is running at ___ load.

The main requirements for maintaining a pneumatic control system include

removing and disassembling valves

The main requirements for maintaining an electric or electronic control system include

checking electrical contacts for pitting

The function of an evaporator is to ___ heat from the ___.

remove; material being cooled

The capacity of an evaporator is affected by the

cleanliness of the evaporator

Basic evaporator configurations depend on whether they have one or more tubes and whether or not they travel

Multiple-circuit evaporators have headers or distributors that direct refrigerant to each coil from ___ expansion valve

A comfort cooler ___ the humidity of moist air by cooling the air to a temperature ___ the dew point.

Unlike a dry-expansion evaporator, refrigerant in a flooded evaporator enters as ___ liquid and exits as ___ vapor.

In a ___ refrigeration system, the refrigerant removes heat from the material to be cooled. This refrigerant then transfers heat to the ___ refrigerant.

A eutectic solution is a brine in which the concentration of salt is precisely set to achieve the lowest possible

Which evaporator arrangement offers the greatest flexibility?

Two evaporators in parallel, each with its own expansion valve

A cascade refrigeration system has more than one

compressor, evaporator, condenser, and refrigerant

The basic law of thermodynamics that apply to refrigeration state that

heat flows from a warmer substance to a cooler substance

The net refrigeration effect can be increased by ___ the refrigerant.

Using a heat exchanger to lower the temperature in the liquid line and raise the temperature in the suction line has the advantage of reducing

the amount of liquid refrigerant entering the compressor

The amount of oil entering tan evaporator can be reduced by using an

If the fluid being cooled by an evaporator circulates through the coil rather than moving slowly or not at all, the performance of the evaporator improves because of the

increased temperature difference across the wall of the evaporator

An evaporator can be defrosted by

reversing the flow of refrigerant

To remove rust, scale, and sludge from a shell-and-tube evaporator, you should use a ___, as necessary.

A water coil can be winterized by draining out the water and

leaving the coil dry for the winter

Frost buildup on an evaporator coil is increased by ___ airflow and ___ air.

Bent fins reduce the cooling capacity of an evaporator, because they

reduce the area exposed to the air

The purpose of the metering device in a refrigeration system is to

control the flow of refrigerant into the evaporator

The operation of an AXV is controlled by the