Note. See also Part Comfort devices.
The air supplied by the ventilation system to the passenger compartment through the filter can be heated or cooled, depending on the user's choice. The heater heat exchanger and the A/C evaporator are located in the passenger compartment, in a housing under the instrument panel. The entire flow of air supplied to the passenger compartment is directed for heating or cooling through the same casing. The temperature and air flow rate are regulated by means of the controls located on the control panel.
The heat generated during engine operation is transferred by the coolant to the heat exchanger of the heating system located in the passenger compartment. The air supplied to the passenger compartment is driven through the heat exchanger and heated by the heat of the coolant flowing inside the latter. The intensity of heating is regulated by mixing in a certain ratio of cold and hot air by changing the position of the mixing damper equipped with a servomotor.
Used air is removed from the passenger compartment through vents equipped with non-return valves.
The flow rate of the air driven through the heat exchanger is controlled by selecting the speed mode of the heater fan.
If necessary, the supply of outside air to the passenger compartment can be blocked by turning on the circulation mode (see part Comfort devices).
Cabin air conditioning system
Functional diagram of a typical A/C system
1 - Heater fan; 2 - Evaporator; 3 - Expansion valve; 4 - Receiver-drier; 5 - Condenser fan; 6 - Capacitor; 7 - Compressor; a - Outside air; b - Heated air vented to the outside; c - Not cooled, blown by a fan; d - Cooled air entering the cabin; A - High pressure gas; B - High pressure liquid; C - Low pressure liquid; D - Low pressure gas
The functional diagram of a typical air conditioning system is shown in the illustration above. Work on the air conditioning system must be carried out by a specialist workshop. Do not open the A/C circuit under any circumstances, as the refrigerant may cause frostbite if it comes into contact with the skin.
The air conditioning system can lower the interior temperature below the ambient temperature. Another function of the K / V is to reduce the humidity of the air supplied to the passenger compartment in wet weather: the air is first cooled, then reheated to a predetermined temperature. Dehumidification allows you to quickly remove condensate from the windows.
The A/C system consists of a condenser located in front of the cooling system radiator, an evaporator located in a common casing with a heater heat exchanger, a compressor, a receiver / dryer, as well as refrigerant pipes connecting the above components. A throttle valve is installed at the evaporator inlet to provide the differential pressure necessary for the operation of the system. As a working fluid in the duct of the A / V system, a refrigerant of the R134a type is used, which changes its state of aggregation depending on the combination of the determining parameters (temperature and pressure).
The fan supplies cabin air to the evaporator, which operates on the opposite principle of the radiator, in which heat is removed from the air and transferred to the refrigerant. When heated, the refrigerant evaporates and at the outlet of the evaporator passes into a gaseous state.
Compressor the air conditioner is driven from the engine crankshaft by means of a belt drive and provides overpressure in the working path of the system up to 30 atm. As a result of adiabatic compression, the refrigerant in the gaseous state heats up. Entering into capacitor, the refrigerant is cooled by the through flow of outside air and converted into a high-pressure liquid. When passing through throttle liquid refrigerant pressure is released. Further, the refrigerant evaporates in the circuit, while being strongly cooled and passing through evaporator, absorbs heat from the air blown through it. The cooled air is supplied to the vehicle interior. As a result of heating in the evaporator, the refrigerant turns into a low-pressure gas and enters the compressor again, after which the process is repeated.
Safety Precautions When Servicing Air Conditioning System Components
Attention! The system is under pressure! Do not attempt to disconnect any pipes related to the air conditioning system without first removing the working fluid from it. Removing fluid from the system is a rather complicated operation that must be performed at a service station. The system contains refrigerant type R134a. Make sure the station has the equipment required for this type of refrigerant. Wear safety goggles when disconnecting the system tubing.
The air conditioning system must only be serviced by trained technicians who are trained in safe work practices, using the proper equipment, in compliance with depressurization rules, and familiar with the methods of collecting and storing automotive refrigerant.
- The R134a refrigerant currently in use is significantly less corrosive than the former R12 refrigerant. However, it is very hazardous to health - if it gets into the eyes and comes into contact with the skin, the refrigerant can cause burns. Although R134a refrigerant is not toxic, its vapors can cause suffocation - never discharge the system in an enclosed area. Remember that refrigerant vapors are heavier than air, try not to climb into the inspection hole during the discharge of the system;
- When refrigerant vapors come into contact with an open flame, poisonous gas is released, which, mixing in a certain proportion with air, can become explosive. Inhaling refrigerant vapors through a lit cigarette can lead to tragic consequences;
- Do not allow refrigerant to enter the atmosphere. Unlike R12, the R134a refrigerant does not cause ozone depletion, but contributes to the development of the greenhouse effect in the atmosphere;
- The A/C system uses sealing elements made of a special material designed to work with a specific type of refrigerant (for 134a - green). In order to accidentally get into the working path of the refrigerant of the wrong type, special adapter nozzles are used when charging the system;
- Discharging the system should be carried out at a Mercedes-Benz branded workshop;
- Before carrying out any work related to the heating of any vehicle components (welding, soldering, drying after painting), the system should be discharged. The need to discharge the system also arises when maintenance of its components is performed;
- When servicing the components of the K / V system, be sure to wear safety glasses;
- If the refrigerant comes into contact with the skin or eyes, do not rub the affected area - immediately rinse it with plenty of cold water, then seek medical attention;
- In a new cylinder, the refrigerant is under pressure. Store the bottle at a temperature not higher than 50°С. Try to prevent the cylinder from falling from a height or other situations that may lead to its damage;
- Maintenance of the components of the A/C system should be carried out in a well-ventilated area - the refrigerant is highly volatile and the accumulation of its vapors can lead to breathing difficulties;
- Cleaning the condenser or evaporator with steam is not allowed, use only cold water or compressed air.