Service Manual

5-30 627333-A
HVAC
heater core - an assembly of metal tubing and fins used
to exchange heat from engine coolant to cab air
Hg - symbol for mercury in Periodic Table of Elements
HVAC - heating, ventilation and air conditioning
high load condition - circumstance when air conditioning
system is operating at maximum capacity to cool a given
environment
high pressure cutout switch - a switch which cuts out
compressor clutch if pressure in system rises above a
pre-set level
high pressure lines - lines carrying high pressure
refrigerant gas and liquid between compressor,
condenser, receiver-drier and expansion valve
high side - high pressure side of system (gas or liquid)
from compressor outlet to expansion valve orifice
high side low pressure cutout switch - a switch (on high
pressure line) which cuts out compressor clutch if
pressure in system drops below a preset level
low side - low pressure side of a system, from expansion
valve orifice to compressor inlet
low side service valve - a valve on compressor used to
service low pressure side of system and permit it to be
checked
lubricant - refrigeration oil specially formulated to be free
of all contaminants and moisture. Note: different from
R-12 and R-134a
magnetic clutch - an electronically operated device used
to cycle compressor on and off
manifold - part of manifold gauge device designed to
control refrigerant flow
manifold gauge hoses - hoses connected to manifold
gauge set used to test, evacuate, recover and charge air
conditioning system
manifold gauge set - a system measuring device
containing two (sometimes three) gauges and three or
more service connections
melting point - temperature at which a solid turns into a
liquid
mercury - used to indicate amount of vacuum (a perfect
vacuum is 29.92 inches of mercury at sea level)
molecular sieve - a drying agent used in receiver-drier to
absorb moisture and filter contaminants out of refrigerant
natures laws - principals of conduct in natural process or
function in nature
PAG - a polyalkylene glycol lubricant used in many
R-134a systems
parallel flow - a coil design where refrigerant flows
through both upper and lower tubing simultaneously
phosgene - a poison gas produced when R-12 comes in
contact with an open flame
POA valve - a suction throttling valve used in some
systems
pressure drop - pressure lost while passing through a
component, difference between pressure in and
pressure out
pressure range - a measured spread between a high
and low pressure
pressure switch - a pressure sensitive electrical switch
mounted at receiver-drier, on some accumulators or in
suction lines to activate or interrupt electrical current
cycling compressor clutch
propane - a flammable gas used in Halide leak detector
PSI - abbreviation for “pounds per square inch”
PSIg - abbreviation for “pounds per square inch gauge”
purge - to remove refrigerant from an AC system and
hoses by opening system or using pressure to eliminate
contents
R-12 - common name of refrigerant used in vehicle air
conditioner systems to move heat energy
R-134a - new refrigerant that does not harm atmosphere
radial compressor - a compressor with pistons in a radial
design
radiation - heat waves (heat energy) passing through air
radiator shutter - a metal vane assembly on some truck
radiators where vanes can be opened or closed to allow
or exclude ram air flow to radiator, radiator mounted
condenser and engine
ram air through which a vehicle passes increasing in
orifice as speed of vehicle increases
receiver-drier - a container which receives, stores and
removes moisture from refrigerant
reciprocating compressor - a compressor having pistons
that move back and forth in cylinders
reclaim - process of restoring refrigerant to new product
specifications
recovery - process of removing refrigerant from an AC
system
recycle - process of removing contaminants (moisture,
acid, particulate matter) from a refrigerant
reed valve - suction and discharge valves located in
valve plate of compressor
refrigerant - a substance used in HVAC systems to
control heat energy
refrigerant cycle - one complete revolution of refrigerant
through system which includes changes of state of
refrigerant from liquid to vapor or gas and back to liquid
refrigeration oil - a specially manufactured oil free from
moisture and all contaminants
relative humidity - amount of moisture in air as
compared to total amount air can hold at a given
temperature and altitude
resistor - a voltage dropping device, usually wire wound,
which provides a means of controlling fan or blower
speed
retrofitting - reconditioning an R-12 AC system to use
R-134a