1.Blower speed control function
Adjusting the amount of the current that passes the blower motor controls the blower speed. There are 2 methods:
resistor and transistor.
(1)Resistor type
This adjusts the amount of current using blower resistor. The construction is that 2 resistors are connected in a series. By operating the selector, the resistance value in the circuit is changed, which varies the amount of current to flow.
When placing the selector in the “LO” position, current passes all the resistors. Therefore, current flowing through the motor is reduced and blower speed becomes low. When placing the selector in the “3” position, current passes only one resistor. When placing the selector in the “HI” position, no current passes any resistors, Therefore, current flowing through the blower motor and blower speed become the highest.
(2)Transistor type
This adjusts the amount of current using a power transistor. Compared to the resistor type, this can control the blower speed at an increased number of levels than the resistor type, so this is mainly used for automatic A/C.
1.Basic theory of cooling
We feel a little cold even on a hot day after swimming. This is because the water on the body takes away the heat when it evaporates from the body.
For the same reason, we feel cool when we apply alcohol to our arms: the alcohol takes away the heat from the arms when it evaporates. We can make objects cooler using these natural phenomena, e.g., by causing a liquid to take the heat from a substance when it evaporates.
A container provided with a tap is placed in a well-insulated box. A liquid that will vaporize readily at atmospheric temperature is placed in the container.
When the tap is opened, the liquid in the container will take away the heat necessary for vaporization from the air inside the box, turn into a gas and escapes outside.
At this time, the temperature of the air inside the box will become lower than that before the tap was opened.