Lesson Notes By Weeks and Term v4 - SHS 3
INTRODUCTION TO VEHICLE TECHNOLOGY
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INTRODUCTION TO VEHICLE TECHNOLOGY
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Applied Technology
Class: SHS 3
Term: 1st Term
Week: 6
Grade code: 3.1.2.LI.6
Strand code: 1
Sub-strand code: 2
Content standard code: 3.1.2.CS.1
Indicator code: 3.1.2.LI.6
Theme: AUTOMOTIVE TECHNOLOGY
Subtheme: INTRODUCTION TO VEHICLE TECHNOLOGY
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This lesson explores two critical aspects of modern vehicle technology: comfort and safety. First, we will demystify the system that keeps us cool on a hot afternoon in Ghana—the Heating, Ventilation, and Air Conditioning (HVAC) system. Understanding how it works is the first step to diagnosing simple problems. Second, we will delve into the principles of safe motoring. With road accidents being a major concern in our country, knowing the safety devices in a vehicle, the rules of the road (Highway Code), and the common causes of accidents is essential knowledge for every future driver, passenger, and responsible citizen.
This lesson is divided into two main parts as per our indicator: The HVAC System and Safe Motoring. Part A: The Automotive HVAC System
HVAC stands for Heating, Ventilation, and Air Conditioning. It is the system responsible for controlling the temperature, humidity, and purity of the air inside the vehicle's cabin. Heating: The heating system uses the engine's own heat. Hot liquid called coolant, which circulates to cool the engine, is passed through a small radiator-like device called a heater core inside the dashboard. A fan blows air over the hot heater core, and this warm air enters the cabin. Ventilation: This is the simplest part. It allows fresh air from outside to be channelled into the cabin, with or without the fan running. Air Conditioning (AC): This is the cooling system. It does not "create cold"; rather, it removes heat from the air inside the car and transfers it to the outside air. It works just like a home refrigerator, using a special fluid called a refrigerant. The Basic AC Refrigeration Cycle
The AC system is a closed loop. The refrigerant continuously circulates and changes its state (from liquid to gas and back again). Let's follow the journey of the refrigerant through the five major components.
The Five Major Components and Their Roles: Compressor: Analogy: The "heart" of the AC system. Function: It is a pump, usually driven by the engine via a belt. It draws in low-pressure, low-temperature refrigerant gas from the evaporator and compresses (squeezes) it into a high-pressure, high-temperature gas. Condenser: Analogy: The "radiator" for the AC system. Location: It is located at the very front of the car, in front of the engine's main radiator. Function: The hot, high-pressure gas from the compressor flows into the condenser. As air flows over the condenser's fins (from the car moving or from a cooling fan), the refrigerant releases its heat to the outside atmosphere. This loss of heat causes the refrigerant to condense into a high-pressure, warm liquid. Receiver-Dryer (or Accumulator): Analogy: The "filter and storage tank" of the system. Function: This component has two jobs. First, it acts as a temporary storage reservoir for the liquid refrigerant. Second, and more importantly, it contains a substance called a desiccant (like the silica gel packets you find in new shoe boxes) that absorbs any moisture (water) that might have contaminated the system. Water in an AC system is very damaging. Expansion Valve (or Orifice Tube): Analogy: A "spray nozzle" or pressure regulator. Function: The high-pressure liquid refrigerant from the receiver-dryer flows to the expansion valve. The valve has a tiny opening (orifice) that the refrigerant is forced through. This causes a sudden, massive drop in pressure. According to physics (the ideal gas law), when pressure drops rapidly, temperature also drops rapidly. The refrigerant emerges as a very cold, low-pressure, fine mist (a mix of liquid and vapour). Evaporator: Analogy: The "freezer unit" inside the car. Location: It is located deep inside the dashboard. Function: This very cold, low-pressure refrigerant flows through the evaporator. The vehicle's blower motor (fan) blows warm cabin air across the evaporator's fins. The refrigerant absorbs the heat from the cabin air. This absorption of heat causes the refrigerant to evaporate (boil) back into a low-pressure, low-temperature gas. The now cold and dry air is what you feel coming out of the vents. The low-pressure gas is then sucked back into the compressor, and the entire cycle starts all over again.