AUT - Chapter 62 - Heating and Air-Conditioning Components and Operation
pilot operated absolute
A POA valve (meaning _________________________________)
vapor
A __________ is a substance that can be easily compressed, has no resistance to flow, and no fixed volume. Since a vapor flows, it is considered a fluid just like liquids are.
solid
A __________ is a substance that cannot be compressed and has strong resistance to flow.
liquid
A ____________ is a substance that cannot be compressed. A substance in a liquid state has a fixed volume, but no definite shape.
pintle valve
A ________________ is a ball-and-seat valve used to increase or decrease the size of the opening.
blower motor
A ______________________ with a squirrel cage-type fan is usually used to force air through the heater core and into the passenger compartment.
positive-displacement compressor
A ___________________________________________________ displaces a constant, uniform volume of refrigerant for each revolution or operating cycle.
electromagnetic clutch
A commonly used method to control evaporator temperature is to use a thermostat to control the compressor. Air-conditioning compressors use an _________________________________.
high-pressure liquid refrigerant
A receiver-drier is used on an air-conditioning system that uses an expansion valve. The receiver-drier is located between the condenser and the evaporator. This section of the air-conditioning system contains ____________________________________________.
32°F (0°C)
A substance is solid at any temperature below its melting point. A melting point is a characteristic of a substance, and is related to the temperature at which a solid turns to a liquid. For water, the melting point is ________________, which means that we can observe changes between liquid water and ice under normal weather conditions.
condensation point
A vapor condenses to liquid if the temperature falls below it. Just like melting and freezing, the boiling point and _____________________________ are the same temperature.
low-pressure gas
After the refrigerant has evaporated into a _________________________ in the evaporator, the refrigerant flows into the engine-driven compressor. The compressor compresses the low-pressure refrigerant gas into a high-pressure gas and forces the refrigerant through the system.
CFC-12; R-12; Freon; chlorofluorocarbon (CFC); dichlorodifluoromethane
Air-conditioning refrigerant is used to transfer heat from the inside of the vehicle to the condenser located in the front of the vehicle. A refrigerant absorbs heat when it changes state from a liquid to a gas. One of the first refrigerants was ___________, commonly referred to as ________ or by its brand name ____________, a registered trade name of the DuPont Corporation. CFC-12 consists of one carbon atom surrounded by two chlorine (CL) and two fluorine (F) atoms and is therefore called a ______________________________________ compound. Its chemical name is ___________________________________. It is the chlorine atoms that are believed to contribute to the destroying of the ozone layer in our upper atmosphere.
compressor
All automotive air-conditioning systems are closed and sealed. A refrigerant is circulated through the system by a _________________ that is powered by the engine through an accessory drive belt.
A voltage source An electrical load (the air-conditioning compressor clutch) A ground connection
All electrical circuits require three things to operate:
Preventing liquid refrigerant from reaching the compressor Holding a reserve of refrigerant Holding the desiccant (helping to remove moisture from the system)
An accumulator is used on systems that use an orifice tube. It is located between the evaporator and the compressor. The refrigerant in this section of the refrigerant cycle is a __________________________. The purposes of the accumulator include:
evaporator pressure regulator
An evaporator pressure regulator valve maintains at least 30 PSI in the evaporator to prevent evaporator freeze-up.
thermostatic expansion valve; TEV or TXV
An expansion valve is attached to the inlet to the evaporator and controls the amount of refrigerant flow into the evaporator. The expansion valve controls the flow of the refrigerant based on the temperature at the outlet of the evaporator, which is measured by a temperature-sensing bulb and tube. When the outlet of the evaporator is warm, the opening of the expansion valve is increased. This opening allows refrigerant to flow into the evaporator. As the temperature at the outlet of the evaporator decreases, the sensing bulb and tube cause the expansion valve to restrict the flow of refrigerant into the evaporator. This type of system is called the _________________________________________ system—usually abbreviated ____________________.
HFC-134a; R-134a; hydrofluorocarbon; tetrafluorolthene
Another refrigerant, _______________, also called ____________, has been selected by vehicle manufacturers to replace the ozone-harming CFC. HFC-134a compound contains two carbon atoms and four fluorine atoms plus two hydrogen atoms and is therefore called a __________________________________. Its chemical name is ___________________________________, and Dupont calls it Suva®
condenses
As the heat travels into the air, the high-pressure gas refrigerant changes state and becomes a high-pressure liquid. This is the reason the condenser is called by that name: as the heat leaves the refrigerant, it __________________from a gas (vapor) to a liquid.
axial compressors
As the pulley turns, the shaft and angled swash plate assembly rotate. This forces the pistons back and forth in their bores. In this way, the swash plate changes the rotating action of the shaft to a reciprocating action that provides driving force for each piston. Compressors that use a swash plate are often called ___________________________.
H-valve
Chrysler uses a valve called an ___________. It includes both the temperature-sensing and pressure-sensing functions of the expansion valve, but does not have any external tubes.
HVAC
Driver and passenger comfort is the primary purpose of the heating, ventilation, and air-conditioning system, often abbreviated ___________.
British Thermal Units (BTU); 252 calories
Heat is also measured in _________________________________. One BTU is the heat required to raise the temperature of one pound of water 1°F at sea level. One BTU equals ____________________.
calories (c)
Heat is measured in _________________.
condensate line
If the carpet (or floor) of the vehicle is wet on the passenger side, the cause is often a clogged evaporator drain hose. The opening, called the _______________________, is frequently clogged with mud, road debris, or leaves.
cycling clutch orifice tube (or CCOT)
Many air-conditioning systems today use a fixed-orifice tube at the inlet to the evaporator. As refrigerant flows through this orifice (small hole), it expands inside the evaporator, where it absorbs heat and expands into a low-pressure gas. A pressure switch located in the low-pressure line at the outlet of the evaporator senses when the pressure is too low. Too low a pressure in the evaporator can cause the temperature of the evaporator to drop to below freezing. A cold evaporator can therefore cause the moisture in the air to freeze into ice, creating a blockage to air flow through the evaporator. Therefore, whenever the pressure drops below a certain pressure (typically about 3 to 33 psi [214 to 228 kPa]), a pressure switch breaks the circuit to the air-conditioning compressor clutch, which stops the flow of refrigerant through the evaporator. Then, when the temperature (and pressure) increases in the evaporator, the pressure switch closes, restoring the electrical current flow to the compressor clutch and causing the compressor to start forcing refrigerant through the evaporator again. This type of system is commonly called a ________________________________________________________ system.
heat; kinetic energy
Molecules in a substance tend to vibrate rapidly in all directions, and this disorganized energy is called ________. The intensity of vibration depends on how much ____________________, or energy of motion, the atom or molecule contains. We measure the level of this energy as temperature.
barrier hoses
Most hoses used on vehicles since the early 1990s use a nonpermeable inside layer of material that prevents the loss of refrigerant through the hose itself. These hoses, called ____________________, are required for use with HFC-134a refrigerant.
POA valve EPR valve
Older vehicles used a system to control evaporator pressure when used with a continuously-operating compressor, including:
solid, liquid, or vapor (gas)
On earth, matter is found in one of three different phases or states:
hygrometer; psychrometer
Relative humidity is commonly measured with a _____________________ or a ____________________.
swash plate
Some compressors use a ________________, or axial plate. This plate is rigidly mounted to the belt-driven shaft at an angle.
degrees
Temperature is measured in _______________.
boiling point
The __________________ is the temperature at which a liquid substance turns to a vapor. For water at normal sea level conditions, the boiling point is 212°F (100°C).
desiccant
The drier contains a ___________________ (usually silica alumina or silica gel). A desiccant is a drying agent that absorbs any moisture (water) that gets into the air-conditioning refrigerant system.
heater hoses; heater core
The engine coolant (antifreeze and water) flows through __________________ and a __________________.
capillary tube
The expansion valve controls the refrigerant flow in response to the temperature of the evaporator outlet, measured by the remotely mounted sensing bulb and ___________________.
latent heat of vaporization
The extra heat required to change a standard amount of water at its boiling point to a vapor is called _______________________________________.
Cool moisture air Moisture being removed from air Cool dry air Heat being added to air Warm dry air
The following parts are also used to control the flow of coolant and therefore control the temperature of the passenger compartment.
superheat
The heat that warms the refrigerant is referred to as _______________.
evaporator
The liquid refrigerant evaporates in a small radiator-type unit called the ________________. As the refrigerant evaporates, it absorbs heat as it changes from a liquid to a gas. As the heat is absorbed by the refrigerant, the evaporator becomes cold.
miscible; synthetic polyalkyline glycol
The oil carried by the refrigerant through the various components is often the only source of lubrication for the compressor. The oil used must be able to be mixed without separating in the refrigerant. This characteristic of being able to be mixed is called ______________. CFC-12 systems must use mineral oil. Mineral oil is not miscible in HFC-134a, and so such systems must use ________________________________________________, usually referred to as PAG oil.
chlorofluorocarbon (CFC)
The ozone (O3) layer is in the upper atmosphere and blocks out ultraviolet rays from the sun. It has been discovered that certain chemicals, such as ________________________________________, are rapidly destroying this layer of ozone, which is 10 to 30 miles above Earth's surface.
reed valve:
The typical valve used in compressors is the ____________ a one-way, flap-type check valve that is built into the valve plate which seals one or more cylinders.
212°F (100°C)
The water in the container on the stove boils at a temperature of ____________________ at sea level, for as long as any liquid water remains.
The temperature at which a liquid boils (and vapor condenses) rises and falls with the pressure. Pressure in a sealed system that contains both liquid and vapor rises and falls with the temperature.
There are two aspects of the relationship between pressure and temperature that are important to understanding the operating of an HVAC system:
condenser
This high-pressure gas flows into the condenser located in front of the cooling system radiator. The _________________ looks like another radiator, and its purpose and function is the same as the cooling system radiator, to remove heat from the high-pressure gas. In the condenser, the high-pressure gas changes (condenses) to form a high-pressure liquid as the heat from the refrigerant is released to the air
Low-pressure switch:
This pressure switch is electrically closed only if there is at least 25 PSI of refrigerant pressure. This amount of pressure means that the system is sufficiently charged to provide lubrication for the compressor. This switch also prevents the air-conditioning compressor from being engaged when the temperature is low (low temperature means low refrigerant pressures).
High-pressure switch:
This pressure switch is located in the high-pressure side of the air-conditioning system. If the pressure exceeds a certain level (typically 375 PSI [2,600 kPa]), the pressure switch opens, thereby preventing possible damage to the air-conditioning system due to excessively high pressure.
Power steering pressure switch:
This switch is used on many vehicles, especially those with four-cylinder engines. It opens the circuit to the air-conditioning compressor clutch when the driver turns the steering wheel. This reduces the load on the engine at the same time power is needed by the power steering pump. Because the wheel is seldom held in a turning maneuver for a long period of time, this stoppage of the air-conditioning compressor has little, if any, effect on passenger cooling.
4°F and 16°F (3°C and 10°C)
Typical values for superheat in an evaporator are between _______________________________________.
solid ice, liquid water, and water vapor
Water occurs naturally in all three states:
thermo switch, icing switch, or defrost switch
When the thermostat senses that the temperature is near freezing, 32°F (0°C), the switch opens the electrical circuit to the compressor and the compressor stops circulating refrigerant. This thermostat switch is also called a ______________________________________________________________.
Humidity
_______________ refers to water vapor present in the air.
Section 609
__________________ of the Clean Air Act required the following: All technicians who service or repair automotive air-conditioning systems shall be properly trained and certified. Recovery and recycling equipment must be properly approved. Each shop that performs automotive air-conditioning service should comply to the Environmental Protection Agency (EPA) that it is using approved recycling equipment and that only properly trained and certified technicians are using the equipment.
Absolute humidity; Relative humidity
_____________________________ is the measurement of the weight of the water vapor in a given volume of air. _____________________________ is the percentage of how much moisture is present in the air compared to how much moisture the air is capable of holding at that temperature.
Thermostatic expansion valve (TXV)
___________________________________________________ systems use a temperature-sensitive bulb located on the evaporator outlet tube.
