Service Manual

5-28 627333-A
HVAC
GLOSSARY OF TERMS
accumulator - a refrigerant storage and filtering
component used in place of a receiver-drier in CCOT air
conditioner systems
activated alumina - chemical agent used in
receiver-driers as a desiccant
air block - an assembly used to direct air pressure to
control devices
air conditioning - control of air movement, humidity and
temperature by mechanical or other means in a vehicle
air operated water valve - a valve in vehicle cooling
(heater) system controlled by air pressure
altitude - a measured height above sea level (where
atmospheric pressure is lower than at sea level)
ambient air temperature - air temperature outside
vehicle
atmospheric pressure - pressure of air at a given altitude
with normal pressure reference point of 14.7 pounds per
square inch at sea level
axial compressor - type of compressor containing
pistons located in an axial design
back seat - an AC service valve position which closes off
service port and allows free flow of refrigerant in system
bellows - a chamber used as a control device in an air
conditioning system which expands and contracts, much
like an accordion
bi-level system - a cab HVAC system where AC output is
diverted to both upper (defrost) and lower air outlets
bimetallic - two dissimilar metals joined together to
function as a thermostat
Binary switch - a two function pressure activated switch
used to prevent compressor damage when pressure is
too high or refrigerant is lost from AC system.
blends - a refrigerant containing less chlorine than R-12.
Proposed as a replacement for R-12, but not a simple
substitute
blower wheel - wheel used to blow air through
evaporator or heater core causing air to circulate in cab
boiling point - point at which liquid changes to vapor
BTU - an abbreviation for British Thermal Unit, a unit of
measure of heat quantity equal to 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, containing 20 or more
pounds of refrigerant
CTC (constant temperature control) - an
electro-mechanical device used to maintain preselected
air temperature
capacity - a measure of unit performance in BTUs per
hour, tons, watts or other unit of measure
capillary tube - a gas-filled tube extending from
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 Fahrenheit
(boiling point of water)
centigrade - another name for Celsius
change of state - 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
charge - term used to describe what happens when
refrigerant is added to an air conditioning system
charging hose - a hose connected to a port on a
manifold gauge set, used to conduct refrigerant into AC
system from refrigerant source
chlorofluorocarbon (CFC) - a family of chemicals which
includes R-12 and other chemicals. Usage is being
phased out under federal law
clutch - a mechanical device which serves to take torque
in a driving force and transfer it to another force to be
driven - used to drive compressor or engine fan
clutch cycling switch - an electrical switch used to turn
compressor clutch on or off according to temperature or
pressure demands (one example: thermostat)
compressor - pump (often referred to as the heat) of an
air conditioning system which pumps refrigerant through
system and raises vapor pressure of refrigerant
compressor head pressure - pressure of refrigerant as it
leaves compressor through discharge port
compressor shaft seal - a seal located on output end of
compressor shaft which serves to keep refrigerant oil
and refrigerant inside system
condensate - water that collects on surfaces like
evaporator fins and other cold surfaces when air
conditioning system is operating
condensation - process by which gas or vapor changes
to a liquid
condenser - a finned tube device (heat exchanger) in
which refrigerant loses heat and changes from hot vapor
(or gas) to a warm liquid in system
conduction - ability of a substance to convey heat from
one point to another within the substance (heat
movement in refrigerant)
contaminant - any foreign substance (particularly
moisture, dirt or air) which enters an air conditioner
system and must be removed
convection - transmitting or moving heat within a liquid or
gas by moving heated parts
cutoff switch - a switch on compressor which cuts
compressor out of system when full throttle is applied to
engine