Audi 100/A6

1990-1997 of release

Repair and car operation

Standard central air consists of several working knots connected among themselves by tight system of tubes. It is filled with a coolant which passes from a liquid form in gaseous and back, transferring heat from salon.

The most important detail on which overall performance of the conditioner depends, the regulating gate which is established on the evaporator placed in salon of the car is. The coolant in the form of liquid under a high pressure arrives via regulating gate in the evaporator where it is sprayed in the form of a gazo-drop mix (fog). The regulating gate can be needle or such as a diaphragm. We will consider the first option.

In the needle gate there is a small opening, and the needle located in an opening is capable more or to block less it, changing thus effective section. The needle is put in action from a temperature-sensitive element placed in the evaporator.

Liquid coolant, passing through a small opening in the gate, evaporates and turns into gas under low pressure. This process is accompanied by sharp temperature drop. The opening less, the becomes colder халадагент, that is the temperature in the evaporator can be regulated, entering or deducing a needle from an opening. The temperature of a surface of the evaporator should be close to a water freezing point, but not below it, differently on the evaporator ice that will complicate movement of air and heat transfer to a coolant will be formed.

As it was already told, instead of the needle gate sometimes, the diaphragm is established. In it there are no moving parts therefore the coolant expense in the evaporator is not regulated, but its giving is supervised by means of the thermorelay or the pressure relay. Having turned into gas of low pressure, the coolant passes on the evaporator (heat exchanger) and selects heat at air in salon. For bigger efficiency of this process the heat exchanger is supplied with edges. Moisture containing in air is condensed on an external surface of the heat exchanger and merges out of salon. Air, having passed through the heat exchanger, comes back to salon colder and dry.

Saved up by a coolant it is warmly necessary to give to the atmosphere, for what the coolant by means of the compressor goes to the condenser (is one more heat exchanger located usually in a forward part of the car).

The compressor, which task – to banish a coolant on system tubes, transferring heat from low temperature level on higher, works by a principle of the pump and is brought by a belt from the engine via the electromagnetic coupling that the conditioner could be disconnected. When the compressor works, he creates depression which "exhausts" a gaseous coolant from the evaporator.

In the compressor pressure of a coolant raises, and it arrives in the condenser, but already in the form of gas under a high pressure. In the condenser gas turns again into the liquid, heat thus containing in it dissipates from a condenser surface in the atmosphere.

From the condenser the coolant – already in the form of liquid under pressure – again moves on regulating gate, and the cycle repeats.

Additional "lotions"

In practice the described base scheme includes still some knots, in particular, a receiver dehumidifier which often (but not always) is mounted between the condenser and the regulating gate. This device (it sometimes call "accumulator") filters a coolant and deletes from it moisture. Sometimes the dehumidifier is supplied with the color indicator which shows when it it it is time to replace its (it means that it gathered a moisture maximum). System of tubes (between the condenser and the evaporator) sometimes build in viewing glass, and then it is possible to watch a coolant condition (existence of unnecessary vials etc.).

The supercharger banishing air through the evaporator, and the fan enter into central air with the thermostat, raising overall performance of the condenser also. Usually the system includes also the pressure sensor with the switch. It is located near a receiver dehumidifier and operates operation of the compressor and the condenser fan, and also supports optimum pressure in system (a miscellaneous for different systems).

In the majority of systems over the evaporator fastens also a heating element. The air stream with the help of "a mixing zaslonka" is distributed between the evaporator and a heater so that to give it desirable temperature.

And how with ecology?

Until recently in automobile conditioners R12 freon was applied. Then it was established that containing in it хлорфторуглероды perniciously influence an ozone layer therefore now to let out R12 in the atmosphere it is forbidden. Besides, under the influence of an open flame of R12 allocates deadly gas phosgene. It is still authorized to fill with it conditioners of former releases as operation of these conditioners is authorized also.

Respectively, the price for R12 freon raises for 5–10 % a month. Eventually it becomes such what to "recharge" old systems begins is simply ruinous. Already now R12 freon costs in the west of $150 for kg, and two years ago cost $65. In modern systems more "harmless" coolant – R134А is used.

The systems calculated on R134A, are arranged so that at service and repair there were no leaks. For this purpose in the right places special valves and other adaptations are established.

Theoretically, R134А can be downloaded and in the old conditioner, having made corresponding changes. However, this coolant of percent on 15 is less effective, than R12 therefore the conditioner of old type with it will worse work. Besides, there is one more problem: the coolant of R134А filters, though is weak, through the hoses made of pure rubber. Special hoses are necessary for this substance with an internal nylon braid. At the same time in old systems so-called "zayershenny" connecting unions which are capable to break through this braid are applied. In a word, it is at present more favorable to use an old coolant.

Generally, there are the so-called "replaceable" coolants which are intended for replacement of R12 and not demanding expensive alteration of system on R134А, but as experts speak, it is impossible and to admit them on a gun shot to the conditioner. Some of these substances contain butane which can ignite in system, besides, it will ruin the test equipment.

If you want to pass from R12 to R134А, it is best of all to change oil together with a coolant (mineral on synthetic) in system to establish a new receiver dehumidifier to replace rubber hoses and to check work of all knots. Then there is a hope that the system will well work.