HVAC Accessories

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HVAC Basic Components

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Control Circuits diagram

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HISTORY OF AUTOMOTIVE AIR CONDITIONING

Automotive air conditioning : that used a refrigerant, was first introduced on the 1940 Packard. Since then , it has become one of the most popular accessories found on car today. Early attempts at automotive air conditioning consisted of evaporative cooler that were hung from the passenger side window.

Water was fed by gravity or capillary action over a filter/screen. Incoming air flowed through the screen into the passenger compartment. The evaporating water absorbed heat from the incoming air. However, the humidity levels inside the car. This made the cooler only practical in the dry, desert climates of the southwestern region of the United States.

The first air conditioners to use a refrigerant were hang-on units. The assembly was mounted under the instrument panel. This unit was independent of the heating, defrosting and ventilation system. The heater core was in separate housing from the evaporator. Operation involves recirculating the from inside the instead of fresh air from the outside.

The next advancement in air conditioning came when the evaporator core was combined in the same housing as the heater core. This referred to a an integrated heating and cooling system. This system allowed the outside air to enter or be recirculated inside the car.

The latest advancement incorporates an Automatis Temperature Control (ATC). Sensors provide information to a computer, which controls the system automatically to maintain the desired temperature setting.

INTRODUCTION OF AUTOMOTIVE AIR CONDITIONING

PURPOSE.
Air conditioning is the controlled environment of an enclosed space, such as inside an auto. Air conditioning involves dehumidifying, cleaning and cooling the air inside the car. This provides comfort to the driver and passenger alike. The main purpose of air conditioning system is to transfer heat from inside the passenger's compartment, to the surrounding outside air.

Comfort affect driver responsiveness and reaction time to a given situation. Air conditioning provides greater safety by reducing driver fatigue. In addiction, interior noise level is reduced when all windows are closed and the air conditioner is on. Air conditioning also eliminates windshields fogging. This allow the driver to maintain good visibility of the road and other cars.


CONDITIONS AFFECTING BODY COMFORT.
The three main factors that effect body comfort are temperature , relative humidity and air movement.
Temperature : Cool air increases the rate of convection; warm air slow it down. Cool air lowers the temperature of the surrounding surfaces. Therefore, the rate of radiation increases. Since warm air raises the surrounding surface temperature, the radiation rate dicreases. In general, cool air increases the rate of evaporation and warm air slows it down. The evaporation rate also depend on the amount of moisture already in the air and the mount of air movement.
Humidity : Moisture in the air is measured in term of humidity. For example, 50% relative humidity means that the air contains half the amount of moisture that is capable of holding at a given temperature. A low relative humidity allows heat to be taken away from the body by evaporation. Because low humidity means the air is relatively dry, it can readily absorb moisture. A high relative humidity has the opposite affect. The evaporation process slows down in humid conditions; thus, the speed at which heat can be removed by evaporation decreases. An acceptable comfort range for the human body is from 22°C to 26.6°C at from 45% to 50% relative humidity.
Air movement : Another factor that effect the ability of the body to give off heat is the movement of air around the body. As air movement increase, the following processes occur:

• The evaporation process of removing body heat speeds up because moisture in the air near the body is carried away at a faster rate.
• The convection process increase because the layer of warm air surrounding the body is carried away more rapidly.
• The radiation process increases because the heat of the surrounding surface is removed at a faster rate. As a result, heat radiates from the body at a faster rate.

As air movement decreases, the processes of evaporation, convection and radiation decrease.

Basic refrigeration and air conditioning system

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What is refrigeration?

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What is air conditioning?

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