WD Catalog 2018

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Glossary
accumulator — a refrigerant storage and filtering
component used in place of a receiver-drier in
CCOT air conditioner systems
activated alumina — one of the chemical agents
used in receiver-driers as a desiccant
air block — an assembly used to direct air pres-
sure to control devices
air conditioning — control of air movement, hu-
midity and temperature by mechanical or other
means in a vehicle
air operated water valve — a valve in the ve-
hicle cooling (heater) system controlled by air pres-
sure
altitude — a measured height above sea level
(where atmospheric pressure is lower than at sea
level)
ambient air temperature — air temperature
outside the vehicle
ambient switch — used to sense outside air tem-
perature and prevent compressor operation in be-
low freezing weather
atmospheric pressure — the pressure of the air
at a given altitude with the normal pressure refer-
ence point of 14.7 pounds per square inch at sea
level
axial compressor — a type of compressor contain-
ing pistons located in an axial design, i.e.
Frigidaire, Sanden, or Zexel (formally Diesel Kiki)
back seat — an AC service valve position which
closes off the service port and allows free flow of
refrigerant in the system
bellows — a chamber used as a control device in
an air conditioning system which expands and con-
tracts much like an accordion
bi-level system — a cab HVAC system where the
AC output is diverted to both upper (defrost) and
lower air outlets
bimetallic — two dissimilar metals joined to-
gether to function as a thermostat
Binary™ switch — a two function pressure acti-
vated switch used to prevent compressor damage
when pressure is to high or refrigerant is lost from
the AC system
blends — a refrigerant containing less chlorine
than R-12. Proposed as a replacement for R-12, but
not a simple “drop in” substitute
blower wheel — wheel used to blow air through
the evaporator or heater core causing air to circu-
late in the cab
boiling point — the point at which liquid changes
to vapor
BTU — an abbreviation for British Thermal Unit,
a unit of measure of heat quantity equal to the
amount of heat energy required to raise a pound of
water one degree Fahrenheit
bulk charge — a large container of refrigerant
used in air conditioning system servicing, contain-
ing 20 or more pounds of refrigerant
CTC™ (constant temperature control), and
CTC II™ — an electro-mechanical device used to
maintain preselected air temperature
capacity — a measure of unit performance in
BTU’s per hour, tons, watts or other unit of mea-
sure
capillary tube — a gas-filled tube extending from
the thermostat and some expansion valves, senses
temperature to close thermostat (clutch) circuit or
open expansion valve orifice
Celsius — a temperature scale where zero degrees
Celsius equals 32 degrees Fahrenheit (freezing),
and 100 degrees Celsius equals 212 degrees Fahr-
enheit (the boiling point of water)
centigrade — another name for Celsius
change of state — the reorganization of matter
which allows a solid to change to a liquid or gas, a
liquid to a solid or gas, or a gas to a solid or liquid
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