The operation of an automobile air conditioner is based on the fact that the radiator-evaporator takes away heat from the air in the cabin and gives it to the refrigerant, which delivers it to the radiator located outside in the air stream. The refrigerant cools - and so on. And the compressor provides circulation of the refrigerant. To understand why such a scheme was needed, school physics will help.
STATE OF AGGREGATION
Automakers use two design schemes. In fig. Figures 1 and 2 show what happens when using the most common one - with a thermostatic valve (expansion valve).
1 no copyright
Fig. 1. Condition of the refrigerant in the air conditioner:
A … B - compression in the compressor
B … C - cooling in the condenser
C … D - processes in the expansion valve or uncontrolled throttle
D … A - processes in the evaporator, the transition of liquid refrigerant into gas. A curved line is the boundary between a liquid and a gas
2 no copyright
The compressor is driven from the engine by a belt through an electromagnetic clutch. Having pumped out cool gaseous refrigerant from the evaporator and compressing it into high-pressure hot gas (A … B in Fig. 1), it feeds it into a condenser installed in front of the engine cooling radiator. Here, having given excess heat to the outside air (B … C), the gas condenses into a liquid that enters the receiver-dryer. The latter is a barrier on the way to the gaseous refrigerant, a reservoir for liquid and a moisture absorber. The refrigerant goes from the receiver to the expansion valve, after which its pressure drops (C … D), and then, inside the evaporator, it boils at a sufficiently low temperature, absorbing the warmth of the interior air (D … A). Finally, cool low-pressure steam is sucked in by the compressor. The circle is complete! We add only that the valve is connected to the inlet and outlet of the evaporator. Feedback matches the refrigerant flow rate to the set temperature in the passenger compartment.
3 no copyright
In fig. 3 system with an unregulated throttle - a capillary tube of constant cross-section. Refrigerant flow rate is unchanged. But if it flows out of the evaporator in liquid, it will damage the compressor - therefore, a dehumidifier is built in front of the compressor. It passes gaseous refrigerant, liquid - it evaporates, and traps moisture.
Alas, the conditioner is not insured against sores. Just note: this system is not one of those where you can climb, armed with courage and pliers. The main problem is that the system is tight, that is, ingress of air or leakage of refrigerant to the outside is unacceptable. Sooner or later they will have to be eliminated in a specialized service - with good specialists, equipment, measuring instruments, necessary materials.
Station for air conditioning
Station for air conditioning. Station for air conditioning.
For a complete diagnosis of the air conditioner, you need a special station that allows you to refuel the system and monitor the pressure drop during its operation. According to the pressure indicators, it is possible to establish a compressor malfunction or obstruction in the system.
To find a refrigerant leak, an electronic “snuffer” will help, giving an audible signal. In addition, when refueling the system, a phosphor is added to the compressor oil. A set for visual inspection (yellow glasses and an ultraviolet lamp) allows you to find a leak on a greenish glow. Everyone else has their own tools.
Electronic "snuffer". Electronic "snuffer".
NOT HOT, NOT COLD
Let's say the air conditioning stopped cooling in a traffic jam. Even worse, if the engine began to overheat at the same time. Is the fan defective? Consider yourself lucky. Sometimes it’s possible to easily fix the problem - for example, by connecting a disconnected connector or changing the fuse. But there are troubles and more complicated. For example, the fan is spinning, but there is no sense.
The air conditioner radiator stands directly in front of the engine radiator, and blowing this “sandwich” with a fan is more difficult than a single radiator. And if a dense coat of mud formed between its parts, it is sometimes impossible. (Dirt is visible only through the gap between the radiators. Usually - from above. And everything seems to be in order in the front.) It is difficult to get rid of this fur coat without undocking the structure. Ideally, you need to remove the radiators and gently wash with a "Karcher". To avoid unexpected problems, the most reasonable is to contact the service.
Sometimes refrigerant vapor escapes through compressor leaks. It happened that a simple bolt tightening eliminated the problem. Refrigerant can also run away in other places. The fact is that the compressor is rigidly mounted on the engine, and the radiators on the body. When the engine oscillates on the supports, its movements are quite significant, and in order to avoid breakage of the system highways, rubber tubes are used. Their connections with the metal pores fail - here the refrigerant gradually evaporates. Part of the compressor oil also leaves with it, without which the unit will not work for a long time. Thus, refueling the system can be considered routine work. The optimal frequency is two years. Well, because of an accident and other damage, including corrosion from road reagents, strong refrigerant leaks can occur. Sometimes they are the result of factory defects. In these situations, the service also can not be avoided.
Layer of dirt on the condenser radiator
Layer of dirt on the condenser radiator. Layer of dirt on the condenser radiator.
Prevent the cooling of a compressor or electromagnetic clutch malfunction. Here are the problems of mechanics: jamming, this couple is even able to stop the engine. If the clutch remains open, it threatens only discomfort for the crew: in the steam room! It is really dangerous when the coupling is at least partially, but closed: under the hood there is a firework of sparks, not far from the fire. When you see this, turn off the engine, and then sort it out. The road, most likely, the same - again to the service.
There are also malfunctions in the control circuit. After pressing the button to turn on the air conditioner, the signal passes through several modules, sensors, connectors. Only a qualified electrician can repeat this path with a probe in hand.