The basic diagram of the movement of refrigerant in the air conditioning system is shown in Fig. 12.2.
The axial piston compressor is mounted on the engine cylinder block and is driven by a poly V-belt.
The compressor ensures the circulation of the refrigerant in the system. The compressor shaft is installed in the aluminum front cover of the housing on bearings and is sealed on the side of the drive pulley with a seal.
The compressor drive pulley is mounted on a double-row ball bearing and rotates continuously when the engine is running. When the air conditioner is turned on, torque is transmitted from the pulley to the compressor shaft through a friction clutch with an electromagnetic drive.
Notes:
- If the system is working properly, a click is heard when the air conditioner is turned on - this is the clutch pressure plate, under the action of an electromagnet, engaging 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 the clutch makes strange noises while rotating, heats up, or smells like burning when the air conditioner is off, then its bearing has probably started to deteriorate. In this case, the bearing must be replaced (see «Replacing the drive pulley bearing»). In some advanced cases, it may be necessary to replace the compressor clutch assembly or its components.
- 2. If you do not hear a click after turning on the air conditioner, the following problems may occur:
- there is a refrigerant leak and the control system is blocking the compressor from turning on; - the pressure sensor in the system is out of order; - faults in the electrical circuits of the control system;
- the clutch electromagnet coil winding burned out;
- engine control unit for some reason (high engine coolant temperature, high engine speed) blocked the compressor from turning on.
- 3. If the clutch rotates easily and freely, but when you turn on the air conditioner, you can clearly hear extraneous noises or even the engine stalls, then most likely the compressor is jammed. The internal pump part of the compressor cannot be repaired. In this case, the compressor will have to be replaced.
- 4. And the last, most insidious option. There is a click, the clutch easily rotates the compressor shaft, but there is no coolness in the cabin. In this case, it only seems that the compressor is working, but in reality it is not pumping anything. Only an experienced specialist with special control and diagnostic equipment can establish the truth.
- The most accurate way to determine the cause of the malfunction is after a complete diagnosis at a specialized service center for repairing car air conditioners.
Condenser (air conditioner radiator) multi-flow type is located in front of the radiator of the engine cooling system. It is attached with four brackets to the tanks of the radiator of the cooling system. The condenser cells are made of flat thin-walled aluminum tubes with internal longitudinal partitions for rigidity and external finning to improve heat exchange. The tanks are aluminum, with flanges for connecting pipelines. The tanks are divided into sections by height, therefore, passing through the condenser, the flow of refrigerant changes direction several times. In the condenser, condensation of vapors of the refrigerant compressed by the compressor and removal of the heat released in this case into the surrounding air occurs.
When the air conditioner is turned on, the engine control unit turns on the power supply circuit of the electric fan of the engine cooling system radiator, which improves heat exchange in the condenser and reduces the pressure in the air conditioning system.
Fig. 12.2. Schematic diagram of the movement of refrigerant in the air conditioning system: 1 - combined pressure sensor; 2 - high-pressure pipeline section; 3 - receiver-dryer; 4 - high-pressure line service valve; 5 - condenser (air conditioner radiator); 6 - radiator fan of the engine cooling system; 7 - air conditioning compressor; 8 - low pressure pipeline section; 9 - low pressure line service valve; 10 - heater fan; I - evaporator; 12 - thermostatic valve
Helpful tips:
- At least once a year, preferably before the start of summer operation, wash the fins A of the condenser honeycomb from adhering dirt, dust and anti-icing reagents B. This will improve heat exchange, reduce the pressure in the system and increase the service life of the system elements.
- Do not use high-pressure water jet washers to clean the condenser. This may damage the thin-walled fin plates.
- Even with regular washing, the need to replace the condenser arises much more often than desired. The fact is that it is the first to take on the flow of anti-icing reagents, dirt and pebbles from the road. And the walls of its tubes are thin. In most cases, the condenser is damaged by corrosion in the third or fourth year of operation.
- If the condenser is damaged due to corrosion, it will be more expensive to repair it. Even if the argon welding specialist manages to patch the hole, a leak may soon appear in another place. By the way, the pressure in the system on hot days can reach 25-28 bar.
- In addition, the complex structure of the condenser tube should be taken into account: it is divided into channels by partitions along the length, so there is a high probability 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 patching the condenser, you will have to pay for removal and installation, welding of the condenser and filling the system with refrigerant. So it is better to install a new condenser right away. Instead of an expensive original one, you can easily buy a cheaper condenser from authorized manufacturers of spare parts.
Evaporator is located in the cabin heating and air conditioning system unit. The evaporator is made of aluminum tubes with external finning to improve heat exchange. Passing through the evaporator tubes, the boiling refrigerant actively absorbs heat from the air blowing on the outer finned surface of the tubes. The air is cooled and supplied to the car interior by a fan.
Note: When the air passing through the evaporator is cooled, the water vapor contained in it condenses. The condensate drains through the drain pipe located on the bottom of the engine shield and under the bottom of the car. If the ambient air humidity is high, a puddle of water may form under the car, which is an indirect sign that the air conditioning system is working properly.
Warning: During vehicle operation, particles of road dust and dirt settle on the wet, condensed outer surface of the evaporator.
- This layer becomes an excellent environment for the life and rapid reproduction of putrefactive bacteria and fungal cultures. Over time, an unpleasant smell appears in the car. It is especially noticeable when the air conditioner is turned off and in humid weather. In order to minimize the risk of this problem, when buying a new car, it is necessary to carry out preventive treatment of the evaporator with special chemicals, regularly replace the cabin filter and clean the drain pipe. If, despite the measures taken, the smell still appears, contact a specialized service for repairing car air conditioners for disinfection or washing the evaporator. If the contamination is very severe, the evaporator will have to be replaced.
Thermostatic expansion valveblock type is located in the evaporator body. After passing through the throttling hole in the valve body, the liquid refrigerant sharply reduces its pressure and begins to boil. A control element is installed in the valve body, changing the flow section of the throttling hole depending on the pressure and temperature of the refrigerant. The control element is adjusted at the manufacturer and is not subject to adjustment during operation.
Receiver-dryer is installed on the condenser on the left side and forms a non-separable unit with it. Inside the housing there is a replaceable filter element (cartridge), filled with desiccant granules (silica gel). There is an opening in the lower part of the housing for replacing the filter element.
Warning: In case of repair or replacement of air conditioning system components, if it was in an open state (some units were removed, pipelines were destroyed, etc.), filter element (cartridge) must be replaced. Otherwise, after filling the system, the refrigerant will not dry out and acids may form inside the system, which will destroy the air conditioner parts from the inside.
Pipelines connect all elements of the air conditioning system into a single hermetic circuit. Pipelines and their mounting flanges are made of aluminum alloys...
...and secured to the body with rubberized holders.
Protect metal sections of pipelines from dents and bends. Any narrowing of the flow section of the pipeline leads to a decrease in the system performance.
Fig. 12.3. Flexible insert hose design: 1 - outer protective shell; 2 - fabric cord of the power frame; 3 - plastic sealing layer; 4 - inner oil-resistant layer
To connect mutually moving elements of the system, pipelines in some sections are equipped with flexible inserts (Fig. 12.3) made of synthetic materials.
In the places of connection of individual elements of the system, sealing rings of circular cross-section made of neoprene are installed. When disconnecting sections of pipelines during repair of the system, sealing rings are subject to mandatory replacement.
Service valves, located on the pipelines, are used to connect diagnostic and filling equipment. To prevent dirt from getting in, the valves are covered with threaded caps.
Note.
- This is how the service valves for the low pressure lines A and high pressure lines B are located on the pipelines.
The valves are equipped with valve cores, similar in design to the valve cores of the tire wheels, but differing in size.
A special key is used to unscrew and screw in the valve cores.
Warning.
- It is prohibited to check for the presence of refrigerant in the system by pressing the service valve spools, since after such a check the valve spool may not close completely and refrigerant will leak from the system!
Pressure sensor is installed in the engine compartment on the right side on the high-pressure line pipeline section. Based on the sensor signals, the electronic engine control unit switches off the air conditioner compressor in the event of a system depressurization or an emergency increase in pressure in it in order to protect the compressor from overloads.
Control unit panelThe heating, air conditioning and ventilation system is installed on the dashboard console.
The controls for the heater, air conditioner and ventilation are described in detail in Section 1 «The structure of the car» (see «Heating, air conditioning and ventilation of the cabin», from 20).
Coolant.The system is filled with HFC134a refrigerant (R134a). The total filling volume is (840±35) G.
The refrigerant contains special oil SP10 for compressor lubrication. It is strictly forbidden to use other types of refrigerants and oils in the system.
Notes:
- During the operation of the car air conditioner, situations arise periodically when the air conditioning system needs to be serviced or repaired. Modern diagnostic and repair equipment is used for this. 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 so-called ultraviolet diagnostics method of air conditioning system tightness is used.
- The method consists of introducing a special dye into the system in microdoses.
- In places of micro leaks, the dye, together with the refrigerant, gradually comes out onto the outer surface of the system elements.
- During the inspection of the system, the dye begins to glow under the influence of ultraviolet rays from a special lamp (fluoresce)...
- ...and the refrigerant leaks become visible.
- It should be noted that the dye does not have any negative impact on the system. It can be in the coolant and circulate in the system for as long as you like and will only serve its purpose if a leak occurs.
- After repairing the car air conditioner, it is necessary to evacuate and fill the system with the appropriate refrigerant (R134a). The volume of air conditioning filling for each car model is individual.
- To perform high-quality refueling of the 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 no more than 5 g) scales for dosing the refrigerant being charged.
Due to the specific features of air conditioning system repair, this section describes only the work on removing and installing individual elements and the system control unit. Work related to filling the system with refrigerant should be carried out in specialized service centers.
Warning. The air conditioning system is filled with refrigerant under high pressure. If liquid refrigerant comes into contact with human skin, it can cause severe frostbite. Therefore, if possible, carry out all work related to servicing, repair or dismantling of air conditioning system components in specialized service centers with professional technological equipment. When carrying out work on your own, take precautions.