Takeuchi TB175W, Руководство по ремонту

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III-56 TB175W
1. Heater Core
Heater cores are like small radiators. The fin and tube construction is de -
signed 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 ei-
ther open, closed or set part way open. Some valves have a bypass design
to return coolant to the engine. Most are manually controlled although elec-
tronic 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 occu -
pant 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 con-
ditioner 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 system 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
difficult 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