III-58
Overview of System Operation
• Truck and Heavy Equipment Systems
• Air Conditioner-System Operation
• Heater System Operation
• Environmental Effects on System Operation
• Chapter Review
Truck and Heavy Equipment Systems
A variety of HVAC systems are in use today, some old and some new. There are:
• Vehicle manufacturer installed systems
• Owner specified systems
• Add-on systems
• Retrofit systems
The system components come in different colors, shapes, and sizes. They may be
mounted in or on the cab in varied locations. Owners or fleet maintenance people can
modify systems by adding controls, auxiliary units or ducts. Major components are
sometimes replaced due to damage or failure. All systems were, at least originally,
designed and installed to meet the needs of an operator. Figure 2-1 includes illus-
trations of various AC and Heater systems. They illustrate system advantages and
disadvantages explained in the paragraphs that follow.
The HVAC system includes both heater and air conditioner components, usually
a common control, and air ducts. The system cools the cab by removing heat energy.
It removes moisture from damp air in the cab and adds fresh outside air to the cab. In
this way, the operator can work comfortably in all kinds of weather.
A sleeper unit, built in or added on, increases the air volumes in the cab. The air
conditioner or heater must circulate and cool or heat a larger amount of air. This is ac-
complished by routing ducts and controls to the sleeper compartment as part of system
design. Components may be increased in size to handle the larger cab air volume. A
bigger heater core, air conditioning evaporator coil, condenser, blower or fan may be
included. Often, on long haul trucks, auxiliary air conditioning and heater components
and controls are added. The objective remains the same, to move heat energy and
maintain occupant comfort.
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