Introduction
Introduction
The air conditioning system tasks
The air conditioning system has two main tasks:
- to lower the air temperature in the passenger compartment to a comfortable level.
- to dehumidify the air (reduce the humidity) that enters the passenger compartment.
Note that the air conditioning expels heat but does NOT create coolness.
The air conditioning is a contained system filled with refrigerant and in principle its function is the same as a normal refrigerator:
- an evaporator which takes the heat from the air and dehumidifies the air.
- a condenser in which the removed heat is transferred to the air.
- in addition there is a compressor and a number of other components in the system.
Lowered passenger compartment temperature - increased traffic safety
It is well documented that the human performance abilities are reduced in heat. Research carried out in traffic and in a normal car demonstrated that when the passenger compartment temperature is increased from 21 to 27°C (70 to 81°F):
- the risk of the driver missing important traffic information (hazard warnings, traffic signals, signs etc.) increased by 50%.
- driver reaction times where 22% slower.
With an air conditioning system, car travel is both more comfortable and safer.
Dehumidified air feels cooler
Sweat evaporates much more quickly if the air is dry. The skin then feels dry and therefore more comfortable.
When the air entering the passenger compartment encounters the cold evaporator, the humidity in the air condenses on the evaporator. The water drains out under the car via a drain hose. In the event of high humidity, this may be considerable quantities of water, which is often mistaken for a water leak from the engine for example.
The water which condenses binds and takes with it some of the dust and the larger impurities in the air. Therefore the air conditioning system also helps to purify the air.
Main air conditioning system components (overview)
There are five main components in the system:
- evaporator
- receiver drier
- compressor
- condenser
- choke valve.
The system is filled with a suitable quantity of refrigerant and oil.
The system has both a low and high pressure side. These are divided by the compressor and the choke valve.
The evaporator is located on the low pressure side and the condenser is on the high pressure side.
The air conditioning system functions only at outside temperatures above approximately 0-5°C (32-41°F) (varies depending on the type of system). At lower temperatures the pressure in the system is too low and the compressor is not engaged.
Evaporator (=air heated heat exchanger)
In the evaporator the heat is transferred from the warm air (the heat is "cooled") to the cold refrigerant.
The refrigerant then begins to boil and is converted to gas form (evaporates).
The blower fan increases the air flow through the evaporator.
Note! In most systems, the blower fan must be operating before the air conditioning system can be engaged.
Receiver drier
The receiver drier has a number of tasks, such as collecting and binding the moisture (water) in the system.
The receiver drier is located on either the low pressure or the high pressure side, depending on the type of system.
Compressor
Sucks refrigerant in gas form from the evaporator.
Compresses the refrigerant thereby increasing its pressure and temperature. The heated refrigerant in gas form passes on to the condenser.
Condenser (= air cooled heat exchanger)
At the condenser, the heat is transferred from the refrigerant to the colder outside air.
The refrigerant then condenses and changes into liquid form.
In most systems there is an electrical fan which increases the air flow through the condenser. This increases the transfer of heat from the refrigerant to the outside air. This of course also increases the capacity of the air conditioning system.
Choke valve
Downstream of the choke valve is the refrigerant in liquid form at high pressure.
The choke valve regulates the amount of refrigerant that flows into the evaporator.