Contents: Engine cooling system ↡ Heating and ventilation system ↡ Air conditioning system ↡ Specifications ↡ Tightening force of threaded…↡
Engine cooling system
All models of the vehicles considered in this Manual are equipped with a positive pressure engine cooling system with thermostatic control of the working fluid circulation. The water pump is fixed to the engine block and pumps the coolant through the cooling tract of the latter. The flow of liquid washes the areas of each cylinder in the block, after which it is directed to the rear of the engine. Cooling channels laid in the block and cylinder head castings provide intensive cooling of the intake and exhaust ports, spark plug installation areas and exhaust valve guides.
From the moment the engine is started, the cooling system goes through three operating modes: at the first stage, until the coolant temperature rises above a certain value, it circulates in a small circle from the working circuit of which the radiator is excluded. As the liquid heats up further, the plate valve of the wax-filled thermostat included in the system tract opens and the radiator is connected to the circulation circuit. Then, when the coolant temperature reaches the next control value, a temperature-sensitive switch is triggered, ensuring the activation of the cooling system fan, the additional air flow pumped by it significantly increases the efficiency of the radiator heat exchanger.
The cooling system has a sealed design and is tightly closed with a radiator/expansion tank cap capable of withstanding a certain excess pressure, which increases the boiling point of the coolant and, accordingly, the efficiency of heat removal through the radiator. When the internal pressure in the system exceeds a certain value, excess coolant flows through the connecting (overflow) tube into the expansion tank. As the system cools, the liquid automatically returns from the tank to the radiator.
Filling the system with coolant is done through the neck of the expansion tank (see Chapter Routine care and maintenance), which simultaneously also acts as a receiver, accumulating the excess liquid displaced from the radiator.
Due to the listed design features, such a cooling system is called closed, since it excludes any functional losses of the working fluid.
On some petrol models, as well as on diesel models with the M612 engine, a preliminary electric heater is built into the water circuit of the cooling system, providing accelerated engine warm-up in cold weather. Power to the heater can be supplied from a 230 or 115 V power supply. The power consumption of the heating element is 500 W.
Note: The electric heater can be installed on the corresponding models individually as an additional accessory.
Heating and ventilation system
The heating system consists of fans and heat exchangers located in the front and rear passenger compartment units. Hot coolant passes through the heat exchangers. When moving the heater control knob located on the control panel (for more details, see Part Comfort devices), the valves open and hot air begins to flow into the car's interior. If you turn on the heater fan, air will be forced into the interior.
Before entering the cabin, outside air is passed through a special filter, in which the bulk of dust particles settle. The cabin filter should be replaced on a regular basis in accordance with the Schedule of routine vehicle maintenance (see Chapter Routine care and maintenance). Violation of the filter permeability leads to a decrease in the performance of the heating/ventilation/air conditioning systems.
[Material borrowed from an online resource Mercedesman.ru]
Distribution of air flows of the ventilation system is carried out by means of dampers. It is possible to switch the air circulation modes. The dampers are driven by means of servomotors.
Air conditioning system
See Section General information and safety precautions.
Specifications
Cooling system
| Cooling system type | Closed, with water pump, thermostat, radiator, fan (electric or with viscous clutch) and a separately installed expansion tank |
| Coolant volume | Cm. Specifications |
| Coolant composition (proportion of antifreeze in the coolant to ensure frost resistance) | |
| 50% |
| 55% |
| Working pressure in the system, atm | 1.4 |
Thermostat
Petrol models
| Valve stroke, mm | not less than 8 |
| Valve activation temperatures, °C | |
| 85÷89 |
| 102 |
Cooling system tract cover
| Operating pressure of the safety valve built into the cover, atm | |
| |
| 1.4 + 1 |
| 1.4 – 1 |
| |
| 1.4 ±1 |
| 2.0 ±1 |
| Depth of vacuum causing the vacuum valve to operate, atm | 0.1 |
| Lid test pressure, atm | 1.4 (the pressure must be maintained by the lid for at least 2 minutes) |
Air conditioning system
| Refrigerant type | R134a |
| Volume of refrigerant, g | |
| 1050 |
| 1070 |
| Compressor oil volume, cm³ | 120 |
| Type of refrigeration oil | Synthetic PAG |
| Amount of compressor oil added when replacing the condenser, cm³ | 20 |
| Amount of compressor oil added when replacing the receiver-dryer, cm³ | 10 |
| Amount of compressor oil added when replacing the refrigeration line, cm³ | 10 |
| The amount of compressor oil to be added after a sudden emptying of the system (destruction of the connecting tract), cm³ | 40 |
Tightening force of threaded connections, Nm
Cooling system
M112/113
| Coolant tract hose clamps | 3 |
| Thermostat housing mounting bolts (M6) | 10 |
| ATF Cooling Line Union Nut on Radiator | 20 |
| Bolt for fastening the fan impeller to the viscous coupling | 10 |
| Bolt for fastening the viscous coupling to the bearing housing (tightened using a special device) | 45 |
| Generator mounting screws | 42 |
| Bolts for fastening the damper of the auxiliary drive belt tensioner | |
| 25 |
| 35 |
| Self-tapping bolts for fastening the water pump to the timing cover | |
| |
| 14 |
| 10 |
| |
| 35 |
| 25 |
| Water pump pulley mounting bolt | 10 |
M612
| Cylinder Head Cover Trim Panel Fastening Screws | 10 |
| Air Distributor Trim Panel Fastening Screws | 10 |
| Thermostat housing mounting bolts | 9 |
| ATF Cooling Line Union Nut on Oil Cooler | 25 |
| Bolt for fastening the fan impeller to the viscous coupling | 10 |
| Bolt for fastening the viscous coupling to the bearing housing (tightened using a special device) | 45 |
| Water pump pulley mounting bolt | 35 |
| Bolts securing the water pump to the timing belt cover | |
| 14 |
| 20 |
M628
| Thermostat housing mounting bolts | 9 |
| ATF Cooling Line Union Nut on Oil Cooler | 25 |
| Bolts for fastening the radiator support beam to the front panel | 19 |
| Water pump pulley mounting bolt | 25 |
| Water pump mounting bolts to engine crankcase | 10 |
| Additional heater circulation pump mounting clamp bolt (STH) | 4 |
Heating/Ventilation/Air Conditioning Systems
| Nut on expansion valve | 10 |
| Bolt for fastening the expansion valve to the evaporator heat exchanger | 8 |
| Mounting a pressure/temperature switch to a pressure line | 8 |
| Compressor mounting bolts | |
| 23 |
| 20 |
| Fastening refrigeration lines to the compressor | |
| 23 |
| 20 |
| Union nut for fastening the refrigeration line to the condenser | 33 |
| Attaching lines to the receiver-dryer | 17 |