Caleb Albaugh
AMT 274
AC Homework 1
Chapter 2
Heating and Air-Conditioning Principles
Review Questions
1. Discuss the changes of state of matter.
A solid is a substance that cannot be compressed and has a strong resistance to flow. A liquid is a
substance that cannot be compressed. When a liquid reaches its boiling point, the substance turns
to a vapor/gas.
2. Discuss the effect of heat and temperature on matter.
Temperature is the measure of the level of energy. Heat is measured in calories, and it expresses
the amount of heat needed to raise the temperature of one gram of water 1 degree Celsius.
3. Discuss the two types of humidity.
Absolute humidity is the mass of water vapor in each volume of air. Relative humidity is the
percentage of how much moisture is present in the air compared to how much moisture the air
can hold at that temperature.
4. Explain heating and cooling load.
Heating load is the term used when additional heat is needed. The actual load is the number of
British thermal units or calories of heat energy that must be added. One way to move heat, called
cooling load, is with a block of ice.
5. Explain the three ways in which heat flows.
The simplest heat movement method is conduction, by which heat travels through a medium
such as a solid or liquid, moving from one molecule of the material to the next. Convection is a
process of transferring heat by moving the heated medium, usually air or a liquid. Radiation is
when heat can travel through heat rays and pass from one location to another without warming
the air through which it passes.
6. Describe the air-conditioning process.
The air-conditioning process works using a fluid, called refrigerant, which continuously changes
state from liquid to gas and back to liquid.
7. Explain the purpose of an HVAC system.
The goal in heating and air conditioning is to maintain a comfortable in-vehicle temperature and
humidity.
Chapter 3
The Refrigeration Cycle
Review Questions
1. Define the terms superheat and sub cooling.
Superheat is defined as the amount of heat added to a vapor above its boiling point. Subcooling
is defined as the amount of heat removed from a liquid below its condensing point.
2. Explain heating and cooling load.
Heat travels from a higher temperature (higher energy level) to a lower temperature (lower
energy level). The flow of a refrigerant through the system is called the refrigeration cycle and is
used to cool the interior of the vehicle.
3. Explain flooded versus starved evaporator.
Abnormal temperatures and pressures indicate that something is wrong, such as the evaporator
might have too much or too little refrigerant. Flooded is too much refrigerant, starved is too little
refrigerant.
4. Explain how the A/C system works.
High-pressure liquid refrigerant flows through an expansion device, which controls the amount
of refrigerant that is allowed to pass through.
5. Identify the low and high side of an A/C system.
Low side—it has low pressure and temperature. The low side begins at the expansion device and
ends at the compressor. The refrigerant boils or evaporates in the low side.
High side—it has higher pressures and temperatures. The high side begins at the compressor and
ends at the expansion device. The refrigerant condenses in the high side. The high-side line is
often called the liquid line.
6. Explain the purpose and function of evaporators in an A/C system.
The evaporator is the heat exchanger and absorbs heat from the passenger compartment.
7. Explain the purpose and function of thermal expansion valves and orifice tube
systems.
A thermal expansion valve (TXV) is a variable valve that changes the size of the valve opening
in response to the cooling load of the evaporator. An orifice tube is a restriction in the liquid line
that forces the refrigerant to expand as it passes through the small opening (orifice).
8. Explain the purpose and function of condensers.
The condenser, like the evaporator, is a heat exchanger. Low-pressure refrigerant vapor is
compressed by the compressor into a high-temperature, high-pressure vapor.
Chapter 4
Air-Conditioning Compressors and Service
Review Questions
1. State the different types of A/C compressors.
Piston compressors, vane compressors, and scroll compressors
2. Discuss the parts and operation of compressor clutches.
The clutch uses a coil of wire where a magnetic field is generated when electrical current flows
through it. The magnetic field pulls the drive plate against the rotating pulley to drive the
compressor.
3. Discuss compressor valves and switches.
Control switches can be located anywhere in the system, including at the following positions:
Compressor discharge, compressor suction cavities, receiver–drier and accumulator
Excessive high-side pressure can produce compressor damage and a potential safety hazard if the
system should rupture.
Many compressors contain one or more of the following:
A low-pressure switch
A high-pressure switch
A low- and/or high-pressure sensor
4. Explain A/C compressor diagnosis and service.
A faulty compressor or compressor clutch is indicated if the following conditions are observed:
The high- and low-side pressures are too close, within 50 PSI (345 k P a).
It cannot produce a high-side pressure of 350 P S I (2,400 k P a) or greater. This test usually
requires disconnecting the fan(s) or blocking condenser airflow.
There is visible damage to the compressor, clutch, or pulley.
Chapter 5
Refrigerants and Refrigerant Oil
Review Questions
1. Discuss the depletion of the ozone layer and the resulting issues of global warming.
A chlorine atom from a chlorinated fluorocarbon (C F C) such as R-12 can travel into the
stratosphere if it escapes or is released.
Under the effects of ice clouds and sunlight, it can combine with one of the oxygen atoms of an
ozone molecule to form chlorine monoxide and an ordinary oxygen molecule, O 2.
This destroys that ozone molecule.
2. Explain the impact of legislative laws on automotive A/C systems.
Clean Air Act
Limits the production of ozone-depleting chemicals.
R-12 production in the United States ceased at the end of 1995.
Section 609
Sales Restriction—Section 609 prohibits the sale of small cans (less than 20 pounds) of C F C-12
to anyone other than an EPA certified technician.
3. Discuss identifying refrigerants and proper storage container.
Refrigerant containers are color coded:
R-12 containers are white
R-22 containers are green
R-134a containers are light blue
R-1234y f are white with a red stripe
4. Explain refrigerant safety precautions.
Wear safety goggles or a clear face shield and protective clothing (gloves) when working with
refrigerants.
Always be in a well-ventilated shop area when working with refrigerants and avoid small,
enclosed areas.
If liquid refrigerant is splashed onto the skin or into the eyes of a human or animal, it
immediately boils and absorbs heat from the body part it is in direct contact with.
If a C F C such as R-12 or R-22 encounters a flame or heated metal, a poisonous gas similar to
phosgene is formed.
5. Discuss the different types and viscosities of refrigerant oils.
Types of Refrigerant Oils
Mineral oil
P A G (polyalkylene glycol)
P O E (polyol ester)
Refrigerant oils are commonly available in several viscosities, including:
46; 100; 150