III-59
Air Conditioner—System Operation
By law, all trucks have a heater/defroster as part of the standard equipment. When there
is a reason to add air conditioning, there are options to meet different needs. The avail-
able space in the cab, operating environment, and owner preference can all play a part
in the type of AC unit selected. You will probably encounter roof-mounted and in-cab
add on systems, and even systems where the condenser is mounted on the roof and the
evaporator is attached to the back panel or mounted under the dash. In cooler climates
you may come across a cab with two heaters, the original and an auxiliary unit.
Air Conditioner—System Operation
We have described the movement of heat energy and basic HVAC system function in
Chapter 1. Now we will go into some detail on how an air conditioner operates. The
system is sealed to keep out air and moisture. To operate properly, the inside of the
system contains a measured amount of refrigerant and special refrigerant oil that keeps
the system lubricated. Figure 2-2 is an illustration of system components without the
cab outline, in-cab controls, component housing, and air ducts or vents. Please study
it for a moment. Note the information printed next to each component. Remember that
the components may be positioned and attached to the truck in various locations.
Figure 2-1
These illustrations show a
basic heater, HVAC system,
the combo system with
sleeper unit, add on AC roof
top and in cab units, roof
mounted condenser and
auxiliary units.
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