Service Manual

627333-A 5-29
HVAC
cycling clutch orifice tube (CCOT) system - a system
using an expansion tube (fixed orifice tube) and an
accumulator in place of expansion valve and
receiver-drier
cycling clutch system - a temperature control system
which monitors operation of compressor clutch
dehumidify - to remove moisture (humidity) from air in
the cab or defog windshield
density - ratio of mass to it’s volume
desiccant - an agent used in an air conditioning system
to dry or remove moisture by absorption; found in
receiver-drier or accumulator
desiccant bag - container found inside some
receiver-driers and accumulators for desiccant
diaphragm - a device which acts as a bellows or piston
to divide chambers of a control device
dichlorodifluoromethane - chemical name for Refrigerant
R-12
discharge - in an air conditioning system, refers to
bleeding or releasing all refrigerant in a system
discharge line - line carrying refrigerant from compressor
outlet to condenser inlet connection
discharge pressure - high side pressure (refrigerant
vapor) leaving compressor
discharge switch (compressor) - switch on compressor
which turns compressor off when low pressure of
refrigerant is sensed
discharge valve - same as high side service valve
drain tube - in an AC system a tube positioned to drain
condensation out of vehicle
drier - normally a part of receiver-drier, used to absorb
moisture in system using a desiccant as a drying agent
drive pulley - pulley that drives compressor clutch
drying agent - same as desiccant
electronic lead detector - a device designed to sense
leaks in an air conditioning system with extreme
accuracy
electronic sight glass - a device using ultra-sonic
principals to sense refrigerant inside an AC system and
provide audible signals when AC system has proper
amount of refrigerant
equalizer line - used to control valves in an air
conditioning system to equalize pressure or temperature
ester - a type of lubricant that may be found in R-134a
systems
evacuate -process of removing all moisture or air in a
system by creating a vacuum in system
evaporation - process by which a liquid changes it’s
state to become a vapor or gas
evaporator - a device with coils and fins through which
liquid refrigerant flows, removing heat energy from air,
and changing to a vapor
expansion tube - also called a fixed orifice tube (CCOT
system), replaces expansion valve and meters
refrigerant to evaporator
expansion valve - same as thermostatic expansion valve
(TXV)
external equalizer - same as equalizer line
Fahrenheit - a scale used to measure temperature (heat
intensity - how hot something is) and calibrated at 32
degrees Fahrenheit where water freezes and 212
degrees Fahrenheit where water boils
fan clutch - a variable speed or on-off clutch which acts
as a coupler (fluid, air or electrical), between engine and
engine cooling fan
filter - a portion of receiver-drier used to remove solid
contaminants from system
flush - process of removing all foreign matter from a
system by means of pressurized air, refrigerant or dry
nitrogen
foaming - when observed in sight glass indicates low
level of refrigerant in system
foot-pound - a measurement of energy required to raise
one pound one foot. In relationship to torque, it is a force
that acts upon a body (such as a bolt or nut) to produce
rotation
freeze-up - freezing of water or moisture in expansion
valve orifice or on fins and coil of evaporator
freezing point - point at which a liquid becomes a solid
Freon - Dupont registered trademark name of refrigerant
R-12
front seat - an AC service valve position which isolates
compressor from system by closing valve (turning valve
stem all the way to the right)
gauge set - two gauges (sometimes three) installed on a
manifold to test and measure conditions inside AC
system
‘H’ valve - a water valve which returns excess coolant
from heater inlet back to engine cooling system
Halide leak detector - a propane gas device used to
determine location and severity of an R-12 lead in
system
head pressure - pressure of refrigerant from where it
originates at discharge valve of compressor, through all
lines and components to orifice in expansion valve
heat energy - heat in action; movement of a quantity of
heat measured in BTUs (example, in a change of state)
heat exchanger - a device which enables fluid at one
temperature (higher) to move heat to another fluid at a
lower temperature
heat intensity - temperature of a substance or material
as measured by a thermometer
heat load - amount of heat contained in a given situation
heat quantity - amount of heat measured in BTUs
(British Thermal Units)
heater - an apparatus providing heat