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Chapter 1
– Air Conditioning / Heating Function
1-8
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Chapter Start - Table of Co ntents- Index
Chapter Review
The following topics were discussed in this chapter:
• The ideal in cab environment for most people is 70 to 80
degrees Fahrenheit,
with a modest humidity level and ad-equate air circulatio
n.• Heavy vehicle cabs a
re hard to cool or to heat becauseof the
weather, minimal in
sulation, and the large glass area of thecab. In summer the
cab picks up heat from the sun, road,
engine, transmission
, and body heat from the occupants. An
operator who spends long periods in the cab can be more
critical of the cab environment.
• We measure heat (energy) two ways—in degrees Fahrenheit
or Celsius, and BTU’s. Degrees measure heat intensity.
BTU’s measure heat quantity.
• One of nature’s laws is that heat (BTU’s) always moves from
a hot area to a cooler area until both are at the same tem-
perature (intensity) in degrees Fahrenheit.
• Another of nature’s laws is that a “change of state” accounts
for the movement of a lot of heat. If the change of state
happens fast, the heat moves fast. When refrigerant changes
state, it can give off or absorb large quantities of heat
(BTU’s).