Takeuchi TL150, Руководство по ремонту

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III-66
1. Heater Core
Heater cores are like small radiators. The fin and tube construction is designed to
route coolant flow for the best possible heat energy transfer from coolant to cab
air. Hoses from and to the engine are connected to the core with clamps. The core
outlet may be larger or the same size as the inlet.
2. Water Valves
Water valves may be cable, vacuum or air controlled. The valve can be either
open, closed or set part way open. Some valves have a bypass design to return
coolant to the engine. Most are manually controlled although electronic systems
are now being installed.
3. Defrosters and Ducts
Defrosting is accomplished by directing heated dry air through ducts to the
windshield. The heater system serves the dual purpose of defrosting and heating.
Controls are used to route the air flow to the windshield and occupant areas by
opening and closing duct doors. Controls may be manual, air or vacuum.
Many vehicles use a “defrost interlock” system which utilizes the air condi-
tioner to dry the defrost air and clear the cab windows more quickly.
4. Blowers and Fans
Blowers or fans are used in the system to move cab air through the heater core
and evaporator. Air can be pushed or pulled through the core depending on sys-
tem design. Blower or fan speed is usually selected by the operator.
Environmental Effects on System Operation
The environment outside the cab involves more than the weather. It may be hot and
humid or cold and dry. That is only part of the condition the HVAC system must handle
to maintain an ideal comfort range. A truck can be at idle, in traffic or moving along
for hours on the Interstate at 65 M.P.H. The load condition on a trip can include going
out full, coming home empty, or driving across the Rockies or Kansas plains during
the day or night. The truck color and shape, the windows and angle of the sun are all
variables that can increase or decrease the “load” on the system. The following are a
few examples of environmental effect:
• A black cab-over (COE) with a dark color interior will be more dif-
ficult to cool than the same vehicle with white paint and a light colored
interior. The black cab picks up and holds the radiant heat from the sun
more easily than the white one.
• In Florida or Houston the humidity in mid summer can be very high
with the temperature in the high 90
·
s or low 100
·
s. The AC unit must
remove a lot of moisture from the air in the cab as the air moves through
the evaporator fins. The more moisture on the fins, the less effective the
transfer of heat is to the refrigerant inside the evaporator coil.
Environmental Effects