Complexity

Lift

Not marked

Rice. 12.1. Scheme of the movement of air flows in the ventilation, heating and air conditioning system: 1 - windshield vents; 2 - dampers for the distribution of air flows to the windshield deflectors and to the instrument panel deflectors; 3 - instrument panel deflectors; 4 - air ducts for heating the driver's and passengers' legs; 5 - damper for the distribution of air flows to the instrument panel deflectors and to the air ducts for heating the driver's and passengers' footwells; 6 - heater radiator; 7 - cabin air filter; 8 - damper of the recirculation system; 9 - air intake box; 10 - air intake in the car; 11 - fan impeller; 12 - fan motor; 13 - air conditioner evaporator; 14 - drainage hole for draining condensate; 15 - damper of the temperature controller; 16 - housing block of the heating and air conditioning system.

Rice. 12.2. Schematic diagram of the movement of the refrigerant in the air conditioning system: 1 - combined pressure sensor; 2 - section of the high pressure pipeline; 3 - receiver-drier; 4 - service valve of the high pressure line; 5 - condenser (air conditioner radiator); 6 - fan of the condenser and radiator of the cooling system; 7 - air conditioner compressor; 8 - section of the low pressure pipeline; 9 - service valve of the low pressure line; 10 - heater fan; 11 - evaporator; 12 - thermostatic valve.

The heating (air conditioning) and ventilation system is a single complex that provides the most comfortable conditions in the car, regardless of weather conditions and driving conditions. The system includes a heater (increases the air temperature in all operating modes of the system), an air conditioner (reduces air temperature and humidity), a fan and air ducts with a filter (provide air exchange in the cabin, purify the air from dust), as well as a control unit (controls all elements systems to obtain the desired comfort parameters).
Note.
The air conditioning system is installed on a part of the production of cars.

Outside air can enter the passenger compartment through the door windows with the windows down and the air blower located in front of the windshield. The air from the blower can enter the passenger compartment through the windshield blower nozzles, side and center nozzles, and also through the lower nozzles of the heater housing.
The interior heating and ventilation system is controlled autonomously from the air conditioning system when performing the function of heating and ventilating the interior, removing frost and condensed moisture from the windshield, as well as blowing the door windows. At the same time, the main elements of the heater work even when the air conditioner is turned on. The units of the heater and the evaporator of the air conditioner are made in one block.
To clean the air supplied to the passenger compartment from the dust contained in the street air, a filter is installed in the heater unit.
The car is equipped with a liquid-type heater. It is integrated with the engine cooling system by two hoses running in the engine compartment.
The main components of the heater (fig.12.1): – heater heat exchanger 6 (radiator), designed to heat the air entering the passenger compartment with the heat of the liquid cooling the engine; – fan 11 with electric drive 12 (air blower), providing a regulated supply of outside air to the dampers of the heater and air conditioner; – damper 15 of the air temperature regulator coming from the heater to the passenger compartment, the amount of air passing through the heater heat exchanger and outside air passing bypassing the heat exchanger depends on the change in its position; – flaps 2 for distributing the air coming from the heater through the air ducts into the passenger compartment or for blowing the windshield.
On fig. 1.7 shows the panel of the control unit for heating (air conditioning) and ventilation of the car interior, installed on the console of the instrument panel.
Switch 18 (see Fig. 1.7) for the intensity of air supply to the passenger compartment operates regardless of the position of the air distribution and temperature regulators and controls the fan speed by changing the voltage in the electric motor power circuit.
The air flow distribution controller 16 and the temperature controller 27 control the heater dampers using cable drives.
The air conditioning system is controlled by means of controls located on a panel shared with the heater.
A compressor-type air conditioning system is installed on a Chery Tiggo car (Fig. 12.2).

Compressor mounted on the engine using a special mounting bracket and is driven by a V-ribbed belt for the drive of auxiliary units.
Compressor of axial-piston type with variable capacity. The compressor shaft is mounted in an aluminum housing on two needle bearings and sealed on the side of the drive pulley with an oil seal. The compressor has seven pistons with Teflon O-rings. Lobe type valves. The capacity regulator is built into the compressor housing.

The drive pulley is mounted on a double-row ball bearing and constantly rotates when the engine is running. When the air conditioner is turned on, the torque from the pulley to the compressor shaft is transmitted through a friction clutch with an electromagnetic drive. The compressor circulates the refrigerant in the system and creates the pressure necessary for the refrigerant to flow through the thermostatic valve opening.
Helpful advice.

If the system is working properly, when the air conditioner is turned on, a click is heard - this is the clutch, under the action of an electromagnet, engages with the drive pulley, and the compressor rotor begins to rotate.
But during the operation of the air conditioner, the following compressor malfunctions may occur.
1. If, when the air conditioner is turned off, the clutch makes extraneous sounds during rotation, heats up, or a burning smell appears, then its bearing has probably begun to collapse. In this case, the bearing must be replaced. In some advanced cases, it may be necessary to replace the compressor clutch or its constituent parts.
2. If, after turning on the air conditioner, a click is not heard, then it is possible: - there was a refrigerant leak, and the electrical control circuit blocks the compressor from turning on; - the pressure sensor in the system has failed; – the electric circuit of management is broken; - The coil of the electromagnetic clutch burned out; – the engine control unit blocked the compressor from being switched on for some reason.
3. If the clutch rotates easily and freely, but when the air conditioner is turned on, extraneous noises are clearly audible or the engine even stalls, then the compressor is most likely stuck.
The internal pump part of the compressor cannot be repaired, the compressor will have to be replaced.
4. And the last, most insidious option. A click is heard, the clutch easily rotates the compressor shaft, and there is no coolness in the cabin. In this case, perhaps the compressor only pretends to work, but in fact it does not pump anything.
Only an experienced specialist in the presence of control and diagnostic equipment can establish the truth. If your compressor has been diagnosed as "lack of compression", then you should be sure that a good specialist has identified the problem. If in doubt, you can re-diagnose and make sure that the cost of purchasing and replacing the compressor is indeed inevitable.
The exact cause of the malfunction can only be determined as a result of a complete diagnosis in a service center for the repair of automobile air conditioners.

In some versions of the compressor, on cover 8 (see Fig. 12.4) of the reed valve block, an emergency pressure relief valve can be installed. In the event of an increase in pressure in the system due to a failure of the pressure sensor or other emergency situations, when the set maximum pressure is exceeded, the valve membrane is destroyed, and part of the refrigerant is released into the street.
As a rule, after this, the emergency valve does not have sufficient tightness.
Therefore, after eliminating the causes that caused the increase in pressure and the discharge of the refrigerant, the valve must be replaced.

Condenser (air conditioner radiator) multi-flow type is installed in front of the radiator of the engine cooling system. The condenser cells are made of flat thin-walled aluminum tubes with internal longitudinal baffles to increase rigidity and external fins to improve heat transfer. Tanks aluminum with flanges for connection of tubes.
The tanks are divided into sections along the height, therefore, passing through the condenser, the refrigerant flow changes direction several times.
In the condenser, vapors of the refrigerant compressed by the compressor are condensed and the heat released in this case is removed to the surrounding air.
When the air conditioner is turned on, the engine control unit turns on the power circuit for the electric fan of the engine cooling radiator. This improves the heat exchange in the condenser and reduces the pressure in the air conditioning system.
Helpful advice.

At least once a year, preferably before the start of summer operation, wash the fins A of the condenser honeycombs from adhering dirt, dust and anti-icing agents B. This will improve heat transfer, reduce pressure in the system and increase the service life of the system elements.
Do not use high pressure water jets to clean the condenser. This may cause damage to the B thin-walled fins.
Even with regular washing, the need to replace the condenser occurs much more often than we would like. The fact is that he is the first to take on the flow of anti-icing reagents, dirt and pebbles from the road. And its tube walls are thin In most cases, the condenser is damaged by corrosion in the third or fourth year of operation.
If the tightness of the condenser is broken as a result of corrosion, then it is more expensive to repair it. Even if the master of argon welding manages to patch the hole, a leak may soon appear elsewhere. By the way, the pressure in the system on hot days can reach up to 25–28 bar.
In addition, the complex structure of the condenser tube should be taken into account: along it is divided into channels by partitions, so it is highly likely that after welding, some of the channels will be blocked. Accordingly, the dissipated power will drop and the operation of the air conditioner will deteriorate, especially in traffic jams and in hot weather.
After each experiment with condenser patching, you will need to pay for removal-installation, welding of the condenser and charging the system with refrigerant. So it is better to immediately install a new condenser. Instead of an expensive original one, it is quite possible to buy a cheaper condenser from authorized spare parts manufacturers.

Receiver dryer installed in the engine compartment on the right side. The body of the receiver is non-separable, made of aluminum alloy. Pipelines are attached to the body of the receiver using flange connections. Inside the housing there is a filter element and a cavity filled with desiccant (silica gel) granules. The liquefied refrigerant passing through the receiver is cleaned of possible impurities, dirt and moisture.
Note.

In case of repair or replacement of elements of the air conditioning system, if the system was in an open state (some components were removed, pipelines were destroyed, etc.), the receiver dryer must be replaced. Without this, after filling the system, the refrigerant will not dry out and acids may form inside the system, which will destroy the parts of the air conditioner from the inside. When purchasing a new receiver, make sure that the connecting pipes are tightly closed with process plugs. A receiver that has been stored without plugs is unusable, even if it is brand new.

thermostatic valve block type is located under the hood near the motor shield. Has flange connections. After passing through the throttling hole in the valve body, the liquid refrigerant abruptly reduces its pressure and begins to boil. A regulating element is installed in the valve body, which changes the flow area of ​​the throttling hole depending on the pressure and temperature of the refrigerant. The control element is set at the factory and is not adjusted during operation.

Evaporator located in a common building with a cabin heater. Manufactured from flat aluminum tubes with external fins to improve heat transfer. Passing through the evaporator tubes, the boiling refrigerant actively absorbs heat from the air blowing over the outer finned surface of the tubes. The air is cooled and blown into the vehicle interior by a fan.
An electronic thermostat sensor is attached to the evaporator. It monitors the surface temperature of the evaporator and, when it drops below the freezing point, sends a signal to the engine control unit to turn off the air conditioning compressor - the evaporator is defrosted.
Note.
When the air passing through the evaporator is cooled, the water vapor contained in it condenses.
Condensate drains through the drain tube under the bottom of the car. If the ambient humidity is high, a puddle of water may form under the vehicle. This is an indirect sign of the health of the air conditioning system.
During the operation of the car on the outer surface of the evaporator, wet from condensate, particles of road dirt and dust settle.

This layer is an excellent environment for life and rapid reproduction of putrefactive bacteria and fungal cultures. Over time, an unpleasant odor develops in the car. It is especially strong when the air conditioner is turned off and in humid weather.
To minimize the risk of this problem, it is necessary when buying a car to carry out preventive treatment of the evaporator with special chemicals and regularly clean the drain tube. If the smell still appears, you should contact a specialized car air conditioning repair service to flush the evaporator. In case of very strong contamination, the evaporator will have to be replaced.

Pipelines connect all elements of the air conditioning system into a single sealed circuit. Pipelines and their fastening flanges are made of aluminum alloys.

Rice. 12.3. The design of the hose of the flexible insert: 1 - outer protective sheath; 2 - fabric cord of the power frame; 3 - plastic sealing layer; 4 - inner oil-resistant layer To connect the mutually moving elements of the system, pipelines in separate sections have flexible inserts (Fig. 12.3) made of synthetic materials.

O-rings made of neoprene are installed at the joints of the individual elements of the system. During the repair of the system, when disconnecting sections of pipelines, sealing rings must be replaced.

The pipelines also have two service valves for connecting diagnostic and refueling equipment.
The valves are closed with threaded caps to protect them from dirt. The caps are marked with the symbols H and L for the high and low pressure lines, respectively.
Note.

This is how the service valves of high A and low pressure B are located on the pipelines.

The valves are equipped with spools, similar in design to the spools of the wheel tires, but differing from them in size.
A special key is used to turn the spools in and out.
Warning.

It is forbidden to check the presence of refrigerant in the system by pressing the spools of the service valves, since after such a check the valve spool may not close completely, and the refrigerant will leak from the system!

Pressure meter combined type is installed on the section of the high-pressure pipeline in the engine compartment. It forcibly turns off the air conditioning compressor in case of depressurization of the system (no more than 1.7 bar) and an emergency increase in pressure in the system (no less than 28 bar) in order to protect the compressor from overloads. At a pressure of 18 bar, the sensor turns on the power supply circuit for fan 6 of the radiator of the engine cooling system, which improves heat transfer in the condenser and reduces pressure in the air conditioning system (see Fig. 12.2).
Note.
The sensor is installed on the pipeline using a threaded fitting with a shut-off valve, so when replacing or checking the sensor can be unscrewed without violating the tightness of the system.
Warnings.

When replacing the sensor, sealing ring A on the threaded fitting of the pipeline must be replaced with a new one and lubricated with oil for the air conditioning system before screwing on the sensor.

Check the condition of the sealing surface on the sensor body. The surface must be clean and smooth.
If there are signs of corrosion, the sensor will have to be replaced.
Coolant. The system is charged with R134a refrigerant. Special oil has been added to the refrigerant to lubricate the compressor. It is strictly forbidden to use other types of refrigerants and oils in the system.
Helpful advice.

The type of recommended oil is indicated on a label affixed to the compressor housing.
Warning.
The air conditioning system is charged with high pressure refrigerant.
Contact of liquid refrigerant on human skin causes severe frostbite, so all work related to maintenance, repair or dismantling of air conditioning system elements should be carried out, if possible, in specialized service centers equipped with professional technological equipment. When working on your own, take precautions. Wear protective goggles.
Notes.
During the operation of a car air conditioner, situations periodically arise when maintenance of the air conditioning system or its repair is required. For this, modern diagnostic and repair equipment is used. The most common situation is the depressurization of the system and the release of refrigerant from it.

Highly sensitive halogen leak detectors with sound indication are used to detect leaks.
In some complex cases, the method of ultraviolet diagnostics of the tightness of the air conditioning system is used.

The method consists in the fact that a special dye is introduced into the system in microdoses.
In places of microflows, the dye, together with the refrigerant, gradually comes to the surface of the system elements.

During the inspection of the system, under the influence of ultraviolet rays of a special lamp, the dye begins to glow (fluoresce)

and refrigerant leaks become visible. It should be noted that the dye does not have any negative effect on the system.
It can be in the refrigerant and circulate through the system for an arbitrarily long time and serve its purpose only when a leak occurs.

After repairing the air conditioner, it is necessary to evacuate and charge the system with the appropriate refrigerant (R134a). The volume of refueling of the car air conditioner for each car model is individual.
To carry out high-quality refueling of a car air conditioner, you need:

– precision manometric blocks with special connecting tips;

– two-stage vacuum pump for complete removal of air and water vapor from the system;

– high-precision (division value d5 g) scales for dosing the charged refrigerant.
Due to the specific features of the repair of the air conditioning system, this section describes only the work on the removal and installation of individual elements and the system control unit. Work related to charging the system with refrigerant should be carried out in specialized service centers.

Modern cars are designed in such a way that a constant flow of fresh air blows over the interior, maintaining the desired temperature even with the windows closed. The outside air can be heated by the engine to keep the windows from fogging up.

Standard heating system

The ventilation system of modern cars provides a constant supply of fresh air and heats it when needed.

Airflow

Air enters a large opening located at the front of the vehicle. When moving in this area, pressure is created that pushes air into the duct. Then the air enters the heater, which, if necessary, heats it. The air intake grille can be located at the top of the hood.

Air enters the passenger compartment through openings located on the dashboard and in the lower part of the body. The fans can be rotated to direct airflow towards the driver and front seat passenger.

Some cars are equipped with fans that direct air to passengers in the back seat.

Airflow from holes in the bar at the bottom of the windshield prevents fogging. In later models, this function is also provided for the side windows.

In many modern cars, the air ducts are equipped with valves that open and close as needed.

Exit holes are provided in the rear of the case. When moving, the pressure on them is reduced, and the air freely escapes.

Heater (stove)

In vehicles with a water cooling system, a bundle of pipes is mounted in the heater housing. The resulting small radiator receives hot water from the engine.

The trapped air is warmed as it passes through the hot water tube bundle.

The ventilation system also contains electric fans that provide air flow when the car is stationary or not moving fast enough.

Electric fans can operate in different modes in accordance with the needs of the driver and passengers.

Methods of thermoregulation

Heating system with water valves

In a heater with water valves, air passes through the tube bundle. The temperature in the beam is determined by the amount of hot water passing through it.

Air Mixing Heating System

In an air-mixing system, pipes are heated to a certain temperature, and warm air is mixed with cold air by the movement of the leaf.

The temperature to which the air is heated is determined by the water valves or the mixing system. Water valves are often found in older models.

A temperature sensor located on the dashboard sends a signal to the faucet, which regulates the amount of hot water supplied to the pipes. This system reacts slowly to changes, so it is almost impossible to set the exact temperature.

The pipes of an air-heated system heat up constantly. The temperature sensor changes the position of the leaf, which mixes the already heated air with the cold air captured from the outside.

Often, such a system can supply cool air to the windshield blower, even if all other fans are running warm air.

The flaps that control the air supply to the heater can be started manually by switching the lever located on the dashboard and connected to the flaps by cables.

In expensive cars, you can see electronic controls that receive information from sensors installed near the inlets.

Air-cooled vehicles

On vehicles with an air-cooled engine, the air in the internal heater can be warmed up by moving over the cooling fins near the hot exhaust manifold.

Thanks to the mixing system with temperature-sensitive valves, the air is brought to the right temperature and maintains a comfortable atmosphere in the cabin.

If necessary, the air is additionally heated by a heat exchanger, which receives heat from the combustion of fuel.

Unlike water systems, in air systems the heat exchanger allows the heater to be powered by the engine. Otherwise, the methods of heat distribution are identical.

In fact, not many drivers are familiar with this mode and know about its useful and negative sides.

Air recirculation in a car is the intake and “distillation” of air masses directly from. In this case, the air is cooled, passing through the air conditioner, and after passing through it is distributed through the air nozzles for supply to the passenger compartment.

pros

When using this mode, the air temperature in the cabin is lowered in faster lines than the mode of intake of air masses from the environment. This is mainly due to the repeated passage of air in the car, the temperature of which is already lower than the environment, through the air conditioner.

With the reverse procedure - heating, it is still easier, since the temperature in the cabin is much higher than outside the car.

Another positive point is the fact that the power consumption for the operation of the compressor is much lower than when taken from outside.

Recirculation is also an indispensable mode for people sensitive to road dust, pollen, unpleasant odors and other allergenic factors.

As an example, it is worth mentioning a situation that is probably familiar to any driver - this is a KAMAZ walking in front of you or any other car that emits strong specific odors, recycling in this case is an excellent way out.

Minuses

One very important point should be attributed to the negative factors of air recirculation - this is the absence of any air exchange. In simple words, you have to breathe the same air.

With prolonged use, fogging of the windows is inevitable due to an increase in humidity in the passenger compartment. Many solve this problem by joint and recycling mode.

Where is the power button

The location of the recirculation button varies depending on the model of your car, but there are two generally accepted symbols (icons) that will make it easy to find them.

The buttons look like this:

These designations are typical, unfortunately, not for all models. For example, on VAZs, the recirculation button looks like a circle of three lines and is located to the left of the temperature control. Or it can look like arrows arranged in a circle.

For those whose car, the question of using or not using this mode largely disappears by itself, as it takes care of the cleanliness and air temperature.

The principle of recycling is applicable not only to cars, but is also actively used at home and in industrial areas.

For example, built-in hoods in the kitchen, which work on the same principle as described above, allow you not to connect to a stationary ventilation pipe, but work through integrated filters.

Outside air can enter the passenger compartment through the door windows with the windows down and the air intake located in front of the windshield on the right and equipped with a dust filter that cleans the air entering the passenger compartment from dust, soot, plant pollen, etc. The air entering the passenger compartment through the air intake passes through the heater. Depending on the position of the handles of the regulators of block 13 (see Fig. 1.6) for controlling heating and ventilation, either heated or cold air enters the car interior.

The arrangement of bodies of distribution of streams of air is shown in fig. 1.8, the location of the heating and ventilation controls - in fig. 1.9.

The following air distribution organs are located in the vehicle interior.

1 - air ducts for supplying air to the legs of passengers in the rear seat.

2 - side nozzles for supplying air to the driver and passenger in the front seat or on the windows of the front doors. The direction of the air flow is regulated by turning the grille (in the vertical direction) and the shutters (in the horizontal direction) by the handle 2 located in the middle of the grille. The flow intensity is regulated by moving the wheel 1 in the vertical direction. At the upper extreme position of the adjusting wheel, the air flow from the left nozzle is maximum, at the lower position, the air flow is blocked. The flow intensity control algorithm from the right nozzle is similar to the left one.

3 - nozzles for blowing windows of the front doors.

4 - nozzles for blowing the windshield.

5 - central nozzles for supplying air to the passenger compartment. The direction of air flows from the central nozzles is regulated in the same way as from the side nozzles (see paragraph 2).

To ventilate the passenger compartment, set the controls and switch of the ventilation and heating control unit to the following positions.

1. Turn the handle of the supply air temperature regulator 2 clockwise until it stops.

4. Set the regulator 3 to the desired air supply speed of the heater electric fan.

5. If the windshield is fogged up, set the regulators of the control unit for the heating and ventilation system, as shown in the photo.

Helpful advice: If the car is equipped with air conditioning, set the temperature control of the supplied air to the leftmost position. This method is most effective in the summer in rainy weather.

To quickly clear the windshield and front door windows of snow and ice, do the following.

1. Turn the regulator knob 1 counterclockwise to the extreme left position, and the regulator knob 2 clockwise to the extreme right position until it stops, as shown in the photo.

2. Set the switch for 3 operating modes of the heater electric fan to minimum speed and gradually, at short intervals, increase the speed of the electric fan by turning the switch clockwise to the maximum. Gradually increasing the speed of the electric fan will prevent the windshield from cracking as a result of a sudden change in temperature.

To quickly warm up the air in the cabin, do the following.

Not all car owners are familiar with the cabin filtration mode, its useful properties, and application features. Consider what is air recirculation in a car and how to use it. In fact, recirculation is the intake of air inside the passenger compartment, filtration through the air conditioner and subsequent distribution through the deflectors.

The main difference between recirculation and a conventional intake is that the air flow comes from the cabin, and not from the outside. The recirculation mode allows you to quickly heat, cool the air, since the temperature in the cabin differs from the temperature outside the car. The climate control system spends less time, power, fuel consumption by the engine.

In practice, few people use this function. Most often, recirculation is used to prevent the penetration of an unpleasant odor into the cabin. For example: the car in front smokes heavily, smokes, a dusty section of the road. In order not to feel these smells, activate the mechanical air recirculation button and block access from the outside.

Positive sides

1. Relatively fast change in flow temperature. One air intake from the outside is equal to 2 - 3 cycles inside the cabin.
2. Heating occurs even faster due to the difference in temperature indicators.
3. The power take-off is 35% lower.
4. An indispensable function for the driver, passengers suffering from allergic reactions, hypersensitivity to odors, dust, pollen.

Negative Factors

• complete absence of clean air from outside. Despite partial filtration during cyclic exchange, the air becomes polluted and gains more harmful substances, humidity increases;
• prolonged inhalation contributes to the development of allergenic diseases;
• prolonged recirculation of air in the passenger compartment leads to fogging of the windows. The problem is eliminated by combining the operation of the air conditioner and filtration.

Health officials and car manufacturers recommend a 15 to 20 minute recirculation mode. After that, be sure to open the windows, start fresh air and ventilate the interior.

Button location and mode activation

Each car has a mechanical button located differently. There is a practice of installing it on the front dashboard in the central part in the area of ​​​​the climate block. To simplify the search, manufacturers use a typical marking - a car with an annular arrow inside the cabin. In the image above, this button is marked with the number 3. When you see it, feel free to activate it, use it. The filtering mode is deactivated in a similar way, only for this a mechanical button with a different pattern is used - an arrow “from the salon” or repeated pressing.

Some domestically produced technical means are not equipped with automatics, and drivers use levers. For example: VAZs of discontinued models have three adjustment levers: supply of cold, hot (warm) flow, closing of the damper by a mechanical drive.

Cars equipped with climate control automatically regulate the temperature and take care of the purity of the air flow. All processes are controlled by an air recirculation sensor. It is installed under the center console of the car. When activated, the controller analyzes the temperature and air content. Household air conditioning equipment operates on a similar principle.

Typical malfunctions

Under the condition of moderate use, careful handling, the service life is unlimited. The failure is facilitated by exceeding the permissible current strength, a short circuit in the circuit, the negative consequences of an accident, an impact.

In practice, there are cases of weak contact between the block and the terminals, blown fuse, mechanical damage.

Do not forget about the periodic ventilation of the cabin. Every second technical inspection, replace the cabin filter, carry out troubleshooting of the air supply channels from the outside.

Video: Air recirculation, how it works.