Heating and air conditioning system. Purpose, device and principle of operation

10.11.1 The purpose of the heating system

The first and most important task of the heating system is to prevent the driver and passengers in the car from freezing at ambient temperatures, that cause discomfort.

The heating system can be a separate component or can be integrated into a common climate control system. 

There are two ways to solve the aforementioned problem: create heat with the help of additional devices or to use free heat, which is a side effect of the internal combustion engine operation. The first method will not be described in this manual. The arrangement of the heating system, the operation of which is based on the principle of extraction of heat from the internal combustion engine, will be described below.

10.11.2 Heating system device

Regardless of whether it is a separate system or an integrated one, the principle of its operation is the same for all the cars and has not changed for quite some time. The basic idea is to use the heat of the engine, which is created during its operation. Due to the fact that the heat from the engine is removed by means of cooling liquid, it will be also necessary for heating system.

A couple of hoses (inlet and outlet ones), a valve (shutter) and a heat exchanger, which is a reduced version of the radiator (shown in Figure 10.15), are installed into the engine cooling system in order to implement the engine cooling system.

Figure 10.15 Simplified diagram of heating system.

10.11.3 Operating principle

With the valve (shutter) closed, the coolant goes its usual way: from the pump through the radiator and thermostat to the engine and back. 

As soon as the driver and/or passengers feel uncomfortable driving inside the passenger compartment, which covered with hoarfrost, the driver shall open the valve (shutter). The coolant, which is warmed up to normal working temperature (and it is 85-90 °C) will flow on the increased circle to the heater heat exchanger. There it will give part of its heat to temporary inhabitants of passenger compartment. In order for hot air to get to where it is needed, the fan of the ventilation system blows air from the environment through the heat exchanger of the heater into the passenger compartment through special ducts.

10.11.4 Purpose of the air conditioning system

Cold air creates discomfort in winter, and in summer – hot air. And in case if in winter one can sit behind a wheel wearing a winter jacket and an ear-muff, as well as gloves or mittens. In summer it will be not so simple to escape from heat. In order to escape into the oasis from the heat, which will be in the driver's seat, designers invented and implemented an air conditioning system. In essence this system is very similar to a refrigerator.

10.11.5 Air conditioning system device

The simplest air conditioning system is arranged as follows (shown in Figure 10.16): the compressor is mounted on the engine and is driven from the crankshaft by the means of a belt. Two high and low pressure hoses are connected to the compressor, a condenser (in a form of a radiator) is installed in front of the cooling system radiator. High and low pressure hoses are connected to the condenser. The receiver-dryer is installed on the condenser, which, in turn, is connected by branch pipes to the expansion valve. An evaporator is installed inside the passenger compartment itself, which is apparently the same radiator, only in a reduced form. The whole air conditioning system is filled with a special refrigerant.

Note
It is worth adding that the air conditioner in the car is not used constantly, even in the summer. Thus, there is no need to pump refrigerant idle on the system. For this purpose, the actuation of the compressor is carried out through the electromagnetic coupling, which is integrated in a compressor pulley. This coupling separates the pulley and the compressor shaft when there is no need for air conditioning.

Figure 10.16 Simplified diagram of air conditioning system.

10.11.6 The principle of the air conditioning system

Thus, in case if you are hot, on the control panel inside the passenger compartment you can press the appropriate button. At that time the clutch connects the pulley to the compressor shaft - and the air conditioner will start. The compressor compresses gaseous freon (refrigerant), which is why it is very hot, and pumps it through a pipeline into a condenser, where the compressed freon is cooled. Additional electric fan facilitates its operation. Upon cooling, the compressed freon condenses and flows out of the condenser already in a liquid form. After that, the liquid freon flows through the receiver-dryer. Here the refrigerant is filtered from the wear products of the compressor and water.

Note
Receiver-dryer has one more important function – it is damping the pulsations of refrigerant.

After cleaning and equalizing the pressure, the freon flows towards the passenger compartment, where the expansion valve is located. While passing through the expansion valve and getting into the evaporator, the freon turns into a gaseous state (boils), while strongly cooling. Cold freon cools the evaporator, and the fan blows the cold air from the evaporator into the passenger compartment. After passing through the evaporator, the still cold enough freon enters the compressor again. The circle is now closed.

Note
The part of the hoses that are situated between the compressor and the expansion valve is called the pressure head, or high pressure line. It can always be identified by hot thin metal tubes. The part from the evaporator to the compressor is called the return line, or the low pressure line. It consists of thick tubes and is cold to the touch. In case if during operation of the compressor pressure inside the pressure line fluctuates from 7 to 15 atm (in emergency cases even up to 30), the pressure inside the return line does not exceed 1-2 atm. When the air conditioner is turned off, the pressure in both lines is equalized and is about 5 atm.