Glossary
1401
boiler. A closed vessel that heats water for circulation
through a hydronic system. (33)
bolt. A threaded fastener designed to screw together with
a nut. (3)
bonding. The creation of a continuous electrical connection
of all the metal parts in an electrical system. (10)
bonnet. The sheet metal chamber in a furnace where heat
collects before being distributed. The bonnet contains a fur-
nace’s heat exchanger. (35)
booster pump. A pump used to move fuel oil from the main
storage tank to a fuel oil accumulator or reservoir tank
nearer to the oil burner. (36)
bore. Cylinder diameter, such as in a reciprocating compres-
sor and referenced when determining its volume of vapor for
calculating the heat-removing capacity of the compressor. (49)
bottom freezer. Refrigerator-freezer in which the frozen
food compartment is located below the fresh food compart-
ment. (17)
Bourdon tube. A thin-walled tube of elastic metal that is
bent into a circular shape and used in pressure gauges. As
pressure inside the gauge is increased, the tube straightens
and moves the needle on the gauge. (7)
box end wrench. A wrench with an enclosed gripping head
that fits over a nut or bolt head. (3)
Boyle’s law. A law stating the inverse relationship between
pressure and volume, provided temperature remains con-
stant. (1)
brazed plate heat exchanger. A heat exchange device com-
posed of a set of thin metal sheets brazed together forming
two separate passageways that share a significant amount of
common surface area. (45)
brazing. A process of joining metal objects with a filler metal
that has a melting point above 840°F (450°C). (4)
breaker strips. Plastic strips that connect a refrigerator cabi-
net’s outer shell to the liner. (20)
brine solution. A water solution to which substances have
been added to raise its boiling temperature and lower its
freezing temperature. (46)
British thermal unit (Btu). A US Customary unit of heat that
is equivalent to the quantity of heat required to raise the tem-
perature of one pound of water one degree Fahrenheit. (1)
brushes. Devices composed of conductive materials used in
an electrical generator to transfer the flow of electricity from
the slip rings to an external circuit. Also used in some dc
motors. (9)
bubble solution. A specialized leak-detection solution or a
solution of soap and water that indicates a leak in tubing by
bubbling as leaking vapor passes through it. (7)
building control system. A master system that controls
all of the individual energy management systems or sub-
systems. (40)
building-integrated solar modules. The components of a
solar system that are included in the building materials, not
added as a separate feature. (39)
building-related illness (BRI). A diagnosable illness caused
by exposure to airborne agents. (22)
built-up terminals. Electrical terminals that are bolted to a
compressor dome. Built-up terminals make it easier for tech-
nicians to install replacement terminals if needed. (12)
burnout. A condition in which the insulation of an electric
motor deteriorates due to overheating. This may be due to
internal problems, such as shorted windings, a locked rotor,
or bearing seizure. The burnout of a motor in a hermetic
compressor can cause contamination problems throughout
the refrigerant circuit. (20, 53)
bushing. A cylindrical sleeve inside a motor bearing that is
used to reduce the friction and wear on the motor shaft as
it rotates. (14)
butterfly damper. A damper used to control airflow in
round ducts. It consists of a disk that rotates on an axis along
the duct’s diameter. (23)
bypass humidifier. A humidifying unit that humidifies air
that is bypassed from the supply air plenum into the return
air plenum. (28)
bypass plug. In an oil-fired heating system, a small plug that
is threaded into the internal bypass between a fuel unit’s
inlet and return ports. The plug forces excess fuel oil to flow
out of the fuel unit’s return port, preventing it from flowing
back to the fuel unit’s inlet. (36)
bypass valve. Three-way valves used to switch refrigerant
flow from one line to another. (16)
cad cell. A light-sensitive resistor used to visually detect an
oil burner’s flame and communicate with a heating system’s
primary control unit. (36)
callback. A service call to repair a problem that had been
improperly repaired. (5)
cap screw. Threaded fastener, which does not require a nut,
designed to hold parts together. (3)
capacitance (C). The ability to store electrical energy in an
electrostatic field, measured in farads (F). (9)
capacitive reactance. The opposition to alternating current
as a result of capacitance, measured in ohms (Ω). Capacitive
reactance causes voltage to lag behind current in a circuit. (10)
capacitor. A device designed to store an electrical charge. In
HVACR, small capacitors are used in control circuitry, while
larger capacitors are used to help start motors and increase
motor efficiency. (9)
capacitor-start, capacitor-run (CSCR) motor. A single-
phase induction motor that has a start capacitor and a run
capacitor wired in series with the start winding. The run
capacitor is kept in the motor circuit during operation to
improve the motor’s efficiency. (12)
capacitor-start, induction-run (CSIR) motor. A single-
phase induction motor that has a start capacitor wired in
series with the start winding. The start capacitor helps to
create high starting torque. (12)
capacity check. For a commercial ice machine, a proce-
dure that involves running through an ice production cycle,
measuring temperatures, timing the length of the cycle,