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TRUCK SERVICE MANUAL
TM 5-4210-230-14&P-1
BODIES AND CABS
Fig. 1. Comfort Control Heating and Air Conditioning System
DESCRIPTION
The Comfort Control, blend air type heater or
combination heater and air conditioner is used in the S-
Series medium and medium heavy vehicles.
In the combination system, both the heater core
and the air conditioning evaporator are housed in the
same unit and utilize the same air ducts, blower and
controls. The functions of each system, however, are
separate and different. This combination system
features
compactness,
convenience,
good
air
distribution and service accessibility. All components
are readily accessible for service resulting in care of
maintenance and low service costs.
The heater and air conditioning systems have
common distribution ducts with an independently
controlled
ventilation
system.
Through
control
arrangement and common ducting of treated air, the
vehicle operator can select any degree of cab interior air
temperature in a wide range of cab heating, defrosting,
cooling
(air
conditioning),
dehumidification
and
ventilation modes.
All of the air treated by the heater and air
conditioning system comes into the unit through the air
intake box. The air intake box has three gravity closed
recirculation doors as well as fresh air supply
connections to the fresh air chamber which is connected
to the fresh air scoop.
From the air intake box, the air goes to the
blower and is "pushed" through the evaporator and
heater cores. In vehicles with A/C, a replaceable filter is
placed ahead of the evaporator to prevent plugging of
evaporator with lint or dirt. Once the air goes through
the filter and evaporator it can either go through the
heater core or bypass the core through the opened
blend door. (Hence the term "blend air".) Temperature
control is achieved through the blend door and water
valve working in combination. Both the water and the
air that goes through the heater core is controlled,
resulting in a nearly linear temperature response and
therefore the best possible cab comfort condition. Once
the air leaves the unit, it has been filtered and either
cooled, dehumidified or heated depending on operator
need.
From the heater/evaporator unit, air enters the
duct system where it can be sent to the defroster
chamber, various register outlets or the floor heat
dumps.
HEATER
AND
AIR
CONDITIONING
SYSTEM
COMPONENTS
The heater portion of the system employs basic
components of any automotive hot water heating
system. These include:
1. Heater Core.
2. Hot Water Flow Control Valve.
CTS-2731 Page 3
PRINTED IN UNITED STATES OF AMERICA
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