figure 4-8 we can cause matter to change state by adding or removing heat

Automotive Heating and Air Conditioning, Fifth EditionBy Tom Birch

© 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

FIGURE 4-1 Heat always moves from hot to cold. In this example, it will travel from the fire to the cooler water and from the hand to the cooler ice.



FIGURE 4-2 Heat can enter a vehicle’s passenger compartment from several sources. The A/C system allows us to move excess heat out of the vehicle. (Courtesy of Toyota Motor Sales USA, Inc.)



FIGURE 4-3 The transfer of heat directly through a material is called conduction. (Courtesy of Chrysler LLC)



FIGURE 4-4 We move heat from the heater to the passengers or from the passengers to the A/C system by convection. Heat movement from the engine to the radiator using circulating coolant is also an example of convection.



FIGURE 4-5 Heated air next to the stove will rise and cooler air will move in to replace it. This creates a convection current to move the air and heat. (Courtesy of Chrysler LLC)



FIGURE 4-6 Heat is transferred from the sun to things on Earth through radiation. (Courtesy of Toyota Motor Sales USA, Inc.)



FIGURE 4-7 Radiant heat entering a vehicle through the windows can add a lot of heat to a car’s interior. (Courtesy of Chrysler LLC)



FIGURE 4-8 We can cause matter to change state by adding or removing heat.



FIGURE 4-9 A water molecule contains two oxygen atoms and one hydrogen atom; R-12 is a combination of one carbon, two chlorine, and two fluorine atoms; R-134a is a combination of two carbon, four fluorine, and two hydrogen atoms; and R-152a has two more hydrogen and two less fluorine atoms than R-134a.



FIGURE 4-10 Ice is a solid form of water with a low temperature and slow molecular action.



FIGURE 4-11 Water is warmer than ice and has a much freer molecular action.



FIGURE 4-12 Adding heat to water produces steam, the gas state, with a much freer molecular action.



FIGURE 4-13 Heat that causes a temperature increase is called sensible heat.



FIGURE 4-14 If we add 970 Btu of heat to 1 lb of water at 212°F,we will have 1 lb of steam at the same temperature.



FIGURE 4-15 If we start with 1 lb of water at 32°F, adding 180 Btu will increase the temperature to 212°F. It will take another 970 Btu (the latent heat of evaporation) to boil that pound of water.



FIGURE 4-16 In an A/C system, the refrigerant changes state and absorbs heat in the evaporator and releases heat as it changes state again in the condenser.



FIGURE 4-17 If we start with a 1-lb block of ice at 32°F, it will take 144 Btu (the latent heat of fusion) to melt all of the ice.



FIGURE 4-18 The amount of heat movement required to change 0°F ice to steam, or vice versa.



FIGURE 4-19 A refrigeration cycle absorbs heat as the refrigerant boils in the evaporator and removes heat as it changes state back to a liquid in the condenser.



FIGURE 4-20 The boiling point of a liquid changes as the pressure changes. Water will boil at 183°F with a pressure of 13 psi on a mountain. It will boil at 212°F at an atmospheric pressure of 14.7 psi. In a radiator at a pressure of 30 psi (absolute), it will boil at 250°F.



FIGURE 4-21 R-12 in a container is a saturated vapor with gas in contact with a liquid. The pressure in the container is in direct relation to the temperature (a); a chart can be used to determine the temperature if we know the pressure, or vice versa (b). (a. Courtesy of Chrysler LLC; b. Courtesy of Four Seasons)



FIGURE 4-22 The weight of the air in our atmosphere generates a pressure of about 15 psi at sea level. Atmospheric pressure and the boiling point of water are lower at higher altitudes (Courtesy of Chrysler LLC)



FIGURE 4-23 As shown on this compound gauge, pressures below atmospheric are commonly called a vacuum (a). A perfect vacuum is 29.92 inches of mercury (b). (a. Courtesy of TIP Instruments; b. Courtesy of Robinair, SPX Corporation)



FIGURE 4-24 The boiling point of water drops as pressure is reduced. At a near-perfect vacuum of 29.9199 δHg or 2.54 microns, the boiling point is 90°F.(Courtesy of Robinair, SPX Corporation)



FIGURE 4-25 The relative pressures between seven different measuring systems.



FIGURE 4-26 Depending on the combination of carbon, chlorine, fluorine, or hydrogen, a refrigerant is classed as an HFC, CFC, or HCFC. (Courtesy of TIF Instruments)



FIGURE 4-27 Comparison of the physical characteristics of R-12 and R-134a. (Courtesy of Zexel USA Corporation)



FIGURE 4-28 Refrigerant is commonly available in small or large (30- or 50-lb) containers. A 30-pound, disposable container of R-12 and small, 12-ounce can of R-134a is shown.



FIGURE 4-29 A refrigerant and its oil must be completely compatible with all of the materials and chemicals in the system.



FIGURE 4-30 The boiling points for R-12, R-22, and R-134a vary depending on the pressure.

figure 4-8 we can cause matter to change state by adding or removing heat

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