CAR COOLER

1.  Preliminary

Air Conditioner is a term for equipment that maintain the indoor air temperature and humidity so nice. If the indoor temperature is high then the heat is extracted to the temperature falls, called by cooling. Conversely when the low temperature heat supplied to the room temperature rises, which is called by heating. In addition to humidity is increased or decreased in order to feel comfortable. Thus the equipment needed for a water conditioner consists of cooler, heater, moisture controllers and ventilators. Air conditioners for cars in general consists of cleaning the heater and cooler with dew (moisture remover) and air flow regulator. Cooler is a device to cool and remove humidity of air or outside air is sucked into the vehicle to make the air feel comfortable.

2.  Basic Refrigeration Theory

We feel a little cold after a swim on a hot day though. This is due to the body absorbs heat and evaporates. With the same reason when we put alcohol in arms, alcohol absorbs heat and evaporation occurs. We can create an object it is cool to use this natural phenomenon, ie when the liquid evaporates it absorbs heat. A vessel that uses tap is inserted into the insulated box. Volatile liquid at atmospheric temperature is inserted into the vessel. If the faucet is opened the fluid that is in the air absorbs heat from inside the box, turn into gas and exit. At this time the air temperature inside the box is cooler than before the faucet is opened. This is how we can cool an object. However, the liquid must be added due to run out. It required that the cooling effect of using the method in which the gas is turned back into liquid and then re-evaporates into a gas.

3.  Refrigeration cycle

- Compressors releasing a high-temperature refrigerant and high pressure as it absorbs heat from the evaporator plus the heat generated during step compressor expenditure (discharge stroke).

- The gas refrigerant flows into the condenser. In the condenser the gas condenses back into liquid refrigerant.

- The liquid refrigerant flows to the receiver that stores and filters the liquid refrigerant to the evaporator requires a refrigerant.

- Expansion valve to change the liquid refrigerant into the liquid mixture and the temperature and low pressure.

- Gas and dewy cold refrigerant is flowing into the condenser. In the condenser the gas condenses back into liquid refrigerant.

cooling cycle image

4. Car Cooler Components

a)      Compressor

The compressor is a pump to raise the refrigerant pressure. Increased pressure means raising the temperature. High-pressure refrigerant vapor in the condenser will quickly condenses by releasing heat to the surroundings.

The compressor is driven by the fan belt from engine pulley. Turnover this compressor will drive the piston / vane and the movement of piston / vane will cause pressure for the gaseous refrigerant so that the pressure is increased which in itself will also increase its temperature.

image compressor

b)      Condenser

Condenser used to cool and absorb heat from the refrigerant gas that has been pressed by the compressor to high temperature, high gas pressure can change this back to a liquid gas. Gas temperature and high pressure refrigerant is compressed by the compressor due, the amount of heat released in the condenser refrigerant gas equal to the heat absorbed in the evaporator heat plus the work needed to suppress the refrigerant compressor. The greater the amount of heat released in the condenser, the greater the cooling effect that would be obtained from the evaporator. Because the condenser is mounted on the front of the vehicle to be cooled by air flow from the engine radiator fan and air flow that occurs during vehicle motion. (Cross flow).

condenser images

c)      Receiver / Dryer

Receiver serves to accommodate the temporary liquid refrigerant that has become the condenser for later menyuplainya accordance with the cooling load, and it is to clean from dirt and moisture detrimental refrigerant cycle. For that in it there is a filter, desiccant, receiver and dryer. At the top there is the sight glass to view refrigerant flow conditions. When the refrigerant-containing impurities (ash), this dirt will tend to cause rust on the functional components. And also can be frozen in the expansion valve orifice and orifice plug and obstruct the flow of refrigerant, or freezing in the evaporator and block the flow of refrigerant. To prevent such interference is then mounted desiccant.

5.  Cooling units

Cooling unit consists of an evaporator, blower and fan, expansion valve and drain the tub mounted in the vehicle. On some models the cooling unit and the blower fan is not included in the cooling unit.

a.       Expansion Valve

The function of the expansion valve is to mengabutkan into an evaporator refrigerant, the hole out on the tool is shaped small holes (orifice) is constant or can be arranged through the valve arrangement used to detect changes in temperatures by a heat sensor. Based on this expansion valve carburetion settings are divided into:

• Expansion valve constant pressure

• Expansion valve type thermal

Opening of valve is very dependent of the size of the pressure Pf of the Heat sensitizing tube. When the temperature of the hole out (out let) where the tool is attached to the evaporator increases, the pressure Pf> Pe + Ps of pressure, the refrigerant that is sprayed will be more. Conversely, if the temperature of the hole out (out let) the evaporator decreases the pressure Pf <Ps + Pe, then the refrigerant is sprayed would be less.
• Ps: pressure spring

• Pe: vapor pressure in the evaporator

image expansion valve

b.      Evaporator

Changes of liquid refrigerant into a gas that occurs in the evaporator will result in heat absorption occurs in the surrounding area, the air that passes through the evaporator grille so that the heat will be absorbed by the blower blowing air out the cabin chamber would be a cool car. (cross flow)

evaporator

blower

Types of evaporators

6.  Additional equipment

Additional equipment found in a series of car air conditioning system. Additional equipment that support the implementation process cooling systems, and also the main equipment that must exist, although not including the main components are:

a.  Pressure Switch

Presure switch serves to control the pressure that occurs at high pressure side, when the pressure of refrigerant cycle too much, either too high (27 kg/cm2) or too low (2.1 kg/cm2) it will automatically stop switch so that the magnetic clutch be off. Abnormal pressure conditions will cause damage to various other components. The location of pressure switch is between receifer and expansion valve (see picture below)
Pressure switch type, there are two kinds:

• single type, with separate switches

• dual type, which to use one switch for the two states is too high or too low

b.  Tools for Preventing Freezing (Anti Frosting Devices)

To avoid the reduced cooling effect caused by freezing water in the evaporator fins that are too cold <0 C, can be paired this equipment which consists of two types, namely
• Thermistor Type a fin attached to the evaporator, and the work based on the signals that control the temperature thermistor fin. When the fin temperature decreases <0C, then the magnetic clutch will die and the compressor will stop spinning.
• Type of EPR (Evaporator Pressure Regulator) coupled between eva porator and compressors, (see picture) This type of regulating the amount of refrigerant flowing from the evapo rator to the compressor, and keep the pressure of not less than 1.9 kg/cm2, so that will keep the temperature fin evaporator does not fall <0C.