Note. See also Part Comfort Chapters Governing bodies.
The air supplied by the ventilation system to the passenger compartment through the filter can be heated or cooled, depending on the choice of the driver and passengers. The heater or air conditioner is located in the cabin, in the 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 heater radiator located in the passenger compartment. The intake airflow from the ventilation system passes through the radiator and is heated by the heat of the engine coolant flowing inside the radiator. The degree of heating is controlled by mixing in a certain ratio of cold and hot air using a mixing damper with a servo.
Used air is removed from the passenger compartment through vents with non-return valves.
The increase in air flow through the heat exchanger is provided by a fresh air fan.
If it is necessary to turn off the fresh air supply, for example in case of a bad smell, the system switches to circulation mode, in which only the air available there circulates in the passenger compartment.
Switching the system to circulation mode is confirmed by the activation of the control lamp (see chapter Controls and techniques for safe operation).
Cabin air conditioning system
Air conditioning circuit diagram
1 - Fan; 2 - Evaporator; 3 - Expansion valve; 4 - Reservoir; 5 - Condenser fan; 6 - Capacitor; 7 - Compressor; a - Outside air for cooling the condenser; b - Warm air vented to the outside; c - Uncooled air passing through the fan; d - Cooled air going into the cabin; A - High pressure, gaseous; B - High pressure, liquid; C - Low pressure, liquid; D - Low pressure, gaseous
The functional diagram of a typical air conditioning system is shown in the illustration. Work on the air conditioning system must be carried out by a specialist workshop. Never open the refrigerant circuit, 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 outside temperature. When the system is operating, the humidity in the passenger compartment decreases. In wet weather, the incoming fresh air is pre-cooled and then reheated to the set temperature. Thus, it is dried. With this procedure, the fogging of the glasses is removed.
The air conditioning system consists of a compressor, condenser, throttle, evaporator, refrigerant tank and connecting pipelines.
The air conditioning 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 damper is installed at the evaporator inlet, which provides the pressure drop 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 provides cabin air to the evaporator, which operates on the principle opposite to the principle of the radiator, in the carburetor heat is taken 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.
The air conditioning compressor is driven by the engine crankshaft through a belt drive and provides overpressure up to 30 atm in the working path of the system. As a result of adiabatic compression, the refrigerant in the gaseous state heats up. Entering the condenser, the refrigerant is cooled by the through flow of outside air and, condensing, turns into a liquid under high pressure. When passing through the throttle, the pressure of the liquid refrigerant is released. Further, the refrigerant evaporates in the circuit, at the same time being strongly cooled and, passing through the evaporator, takes away 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 circulation 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. Avoid contact with eyes or skin - you may get burned. Although not toxic, its fumes can cause suffocation - do not remove it from the system while in an enclosed area. Its vapors are heavier than air, so do not stand under the vehicle when removing it from the system;
- Keep refrigerant vapors away from open flames. When it burns, poisonous gas is released. Gas mixed with air in a certain proportion can become explosive. Inhalation of vapors through a lit cigarette can lead to tragic consequences;
- Do not allow refrigerant to enter the atmosphere. Unlike R12, R134a type refrigerant does not cause ozone depletion, but leads to the appearance of a greenhouse effect in the atmosphere;
- The system uses seals made of a special material designed to work with a given type of refrigerant (for 134a - green). In order not to accidentally mix different types of refrigerants, certain types of adapters are used to charge a specific type of refrigerant;
- The system should be discharged at a Mercedes-Benz workshop;
- Before carrying out any work related to the heating of any vehicle components (welding, soldering, drying after painting), discharge the system. It is also necessary to discharge the system before servicing any of the components of the air conditioning system;
- Wear protective goggles when working near the air conditioning system;
- If refrigerant comes into contact with skin or eyes, do not rub the affected area. Rinse immediately with cold water for at least 15 minutes. Contact a doctor or health facility immediately. Self-medication is not allowed;
- In a new cylinder, the refrigerant is stored under pressure. Store the cylinder at a temperature not exceeding 50°C. Take measures to prevent the cylinder from falling from a height or other situations that may lead to its damage;
- Work should be carried out in a well-ventilated area - the refrigerant is highly volatile and the accumulation of its vapors can lead to difficulty breathing;
- The gaseous refrigerant is heavier than air and must collect relatively quickly at the bottom, for example, under a car;
- Cleaning the condenser or evaporator with steam is not allowed, use only cold water or compressed air.