WD Catalog 2018

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4-17 - -
HEATER CORE
HEATER WATER VALVE
EVAPORATOR CORE
BLOWER
OUTSIDE
AIR INLET
CAB AIR INLET
MODE
DOOR
AC
OUTLET
DEFROSTER
DOOR
DEFROSTER
OUTLET
HEATER
OUTLET
HEATER CORE
EVAPORATOR CORE
BLOWER
AIR FLOW
Air Conditioner Hoses and Fittings
The refrigerant hoses used in air conditioning systems are much stronger than
heater or radiator hoses because of pressure restraints. These are available in
single braid, double braid and nylon lined rubber hoses.
Fittings of many types, shapes and sizes may be used depending on the
application and location. There are push on, flare, O-ring and quick disconnect
fittings. Various adapter, step up, tee block, splicer and special application
fittings may be used as connectors during initial installation, service or when a
system is modified.
Chapter Review
• The standard refrigerants used in vehicle air conditioning sys-
tems are R-12 and R-134a. Although safe to use, a refrigerant
may be dangerous if not handled carefully. At sea level
pressure, a refrigerant will boil at a very low temperature.
A refrigerant can be controlled to change it’s state inside the AC
system and absorb, move and give up a large amount of heat
energy. A refrigerant is cold in the evaporator and hot in the
condenser.
Chapter Review
Figure 4-14
This HVAC system cutaway
drawing shows the various
duct doors and the air flow
pattern. Most heavy duty
HVAC systems have a
stacked core arrangement
where air passes through
both coils.
Figure 4-15
This is a cutaway of a stan-
dard stacked core arrange-
ment.