汽車空調小常識

m.guilinhy.com 來源：互聯網作者：永不放汽.. 類別：汽車電器維修時間：2007-08-19

Automotive Air Conditioning Systems

Today, as we drive our automobiles, a great many of us, can enjoy the same comfort levels that we are accustomed to at home and at work. With the push of a button or the slide of a lever, we make the seamless transition from heating to cooling and back again without ever wondering how this change occurs. That is, unless something goes awry.

Since the advent of the automotive air conditioning system in the 1940's, many things have undergone extensive change. Improvements, such as computerized automatic temperature control (which allow you to set the desired temperature and have the system adjust automatically) and improvements to overall durability, have added complexity to today's modern air conditioning system. Unfortunately, the days of "do-it-yourself" repair to these systems, is almost a thing of the past.

To add to the complications, we now have tough environmental regulations that govern the very simplest of tasks, such as recharging the system with refrigerant R12 commonly referred to as Freon® (Freon is the trade name for the refrigerant R-12, that was manufactured by DuPont). Extensive scientific studies have proven the damaging effects of this refrigerant to our ozone layer, and its manufacture has been banned by the U.S. and many other countries that have joined together to sign the Montreal Protocol, a landmark agreement that was introduced in the 1980's to limit the production and use of chemicals known to deplete the ozone layer.

Now more than ever, your auto mechanic is at the mercy of this new environmental legislation. Not only is he required to be certified to purchase refrigerant and repair your air conditioner, his shop must also incur the cost of purchasing expensive dedicated equipment that insures the capture of these ozone depleting chemicals, should the system be opened up for repair. Simply put, if your mechanic has to spend more to repair your vehicle - he will have to charge you more. Basic knowledge of your air conditioning system is important, as this will allow you to make a more informed decision on your repair options.

Should a major problem arise from your air conditioner, you may encounter new terminology. Words like "retrofit" and "alternative refrigerant" are now in your mechanics glossary. You may be given an option of "retrofitting", as opposed to merely repairing and recharging with Freon. Retrofitting involves making the necessary changes to your system, which will allow it to use the new industry accepted, "environmentally friendly" refrigerant, R -134a . This new refrigerant has a higher operating pressure, therefore, your system, dependant on age, may require larger or more robust parts to counter its inherent high pressure characteristics. This, in some cases, will add significantly to the final cost of the repair. And if not performed properly, may reduce cooling efficiency which equates to higher operating costs and reduced comfort.

Vehicles are found to have primarily three different types of air conditioning systems. While each of the three types differ, the concept and design are very similar to one another. The most common components which make up these automotive systems are the following:

COMPRESSOR, CONDENSER, EVAPORATOR, ORIFICE TUBE, THERMAL EXPANSION VALVE , RECEIVER-DRIER, ACCUMULATOR. Note: if your car has an Orifice tube, it will not have a Thermal Expansion Valve as these two devices serve the same purpose. Also, you will either have a Receiver-Dryer or an Accumulator, but not both.

COMPRESSOR

Commonly referred to as the heart of the system, the compressor is a belt driven pump that is fastened to the engine. It is responsible for compressing and transferring refrigerant gas.

The A/C system is split into two sides, a high pressure side and a low pressure side; defined as discharge and suction. Since the compressor is basically a pump, it must have an intake side and a discharge side. The intake, or suction side, draws in refrigerant gas from the outlet of the evaporator. In some cases it does this via the accumulator.

Once the refrigerant is drawn into the suction side, it is compressed and sent to the condenser, where it can then transfer the heat that is absorbed from the inside of the vehicle.

CONDENSER

This is the area in which heat dissipation occurs. The condenser, in many cases, will have much the same appearance as the radiator in you car as the two have very similar functions. The condenser is designed to radiate heat. Its location is usually in front of the radiator, but in some cases, due to aerodynamic improvements to the body of a vehicle, its location may differ. Condensers must have good air flow anytime the system is in operation. On rear wheel drive vehicles, this is usually accomplished by taking advantage of your existing engine's cooling fan. On front wheel drive vehicles, condenser air flow is supplemented with one or more electric cooling fan(s).

As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.

EVAPORATOR

Located inside the vehicle, the evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal.

The ideal temperature of the evaporator is 32° Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it can absorb large amounts of heat. This heat is then carried off with the refrigerant to the outside of the vehicle. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 32° F. Temperature and pressure regulating devices must be used to control its temperature. While there are many variations of devices used, their main functions are the same; keeping pressure in the evaporator low and keeping the evaporator from freezing; A frozen evaporator coil will not absorb as much heat.

PRESSURE REGULATING DEVICES

Controlling the evaporator temperature can be accomplished by controlling refrigerant pressure and flow into the evaporator. Many variations of pressure regulators have been introduced since the 1940's. Listed below, are the most commonly found.

ORIFICE TUBE

The orifice tube, probably the most commonly used, can be found in most GM and Ford models. It is located in the inlet tube of the evaporator, or in the liquid line, somewhere between the outlet of the condenser and the inlet of the evaporator. This point can be found in a properly functioning system by locating the area between the outlet of the condenser and the inlet of the evaporator that suddenly makes the change from hot to cold. You should then see small dimples placed in the line that keep the orifice tube from moving. Most of the orifice tubes in use today measure approximately three inches in length and consist of a small brass tube, surrounded by plastic, and covered with a filter screen at each end. It is not uncommon for these tubes to become clogged with small debris. While inexpensive, usually between three to five dollars, the labor to replace one involves recovering the refrigerant, opening the system up, replacing the orifice tube, evacuating and then recharging. With this in mind, it might make sense to install a larger pre filter in front of the orifice tube to minimize the risk of of this problem reoccurring. Some Ford models have a permanently affixed orifice tube in the liquid line. These can be cut out and replaced with a combination filter/orifice assembly.

THERMAL EXPANSION VALVE

Another common refrigerant regulator is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. Several variations of this valve are commonly found. Another example of a thermal expansion valve is Chrysler's "H block" type. This type of valve is usually located at the firewall, between the evaporator inlet and outlet tubes and the liquid and suction lines. These types of valves, although efficient, have some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.

RECEIVER-DRIER

The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R -134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R -134a . The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R -134a refrigerants.

ACCUMULATOR

Accumulators are used on systems that accommodate an orifice tube to meter refrigerants into the evaporator. It is connected directly to the evaporator outlet and stores excess liquid refrigerant. Introduction of liquid refrigerant into a compressor can do serious damage. Compressors are designed to compress gas not liquid. The chief role of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is a good idea to replace the accumulator each time the system is opened up for major repair and anytime moisture and/or debris is of concern. Moisture is enemy number one for your A/C system. Moisture in a system mixes with refrigerant and forms a corrosive acid. When in doubt, it may be to your advantage to change the Accumulator or receiver in your system. While this may be a temporary discomfort for your wallet, it is of long term benefit to your air conditioning system.

汽車空調系統

一．汽車空調的工作原理

今天，當我們駕駛汽車，行駛在公路上，我們當中的許多人都能夠感受到同等的舒適感覺，就像我們非常熟悉的家和辦公室一樣。您只需要按一個按鈕或是拉動控制桿，就可以使溫度在冷熱之間來回轉換。自從十九世紀四十年代，汽車空調系統的誕生，很多事情都發生了前所未有的改變，這總創新就像計算機自動溫度控制系統（用戶可以設置自己想要的溫度或是讓系統自動調節所需溫度）。其實汽車空調和我們熟悉的家用空調制冷原理是一樣的。都是利用R12（由DuPont生產研制出來的）或是R134a壓縮釋放的瞬間體積急劇膨脹就要吸收大量熱能的原理制冷。(由于廣大的科學學者已經證明了R12對大氣臭氧層的破壞作用，美國已經禁止了這個廠商生產這種制冷劑。還有許多其他國家聚集在一起簽訂了蒙特利爾協議，在19世紀80年代，達成了一個跨世界的協定，規定禁止生產和使用對臭氧層有危害的化學藥品，出于環保的要求發達國家從1996年開始改用R134a做制冷劑)汽車空調的構造和家用的分體空調類似，它的壓縮機往往是安裝在發動機上，并用皮帶驅動（也有直接驅動的），冷凝器安裝在汽車散熱器的前方，而蒸發器在車里面，工作時從蒸發器出來的低壓氣態致冷劑流經壓縮機變成高壓高溫氣體，經過冷凝器散熱管降溫冷卻變成高壓低溫的液體，再經過貯液干燥器除濕與緩沖，然后以較穩定的壓力和流量流向膨脹閥，經節流和降壓最后流向蒸發器。致冷劑一遇低壓環境即蒸發，吸收大量熱能。車廂內的空氣不斷流經蒸發器，車廂內溫度也就因此降低。液態致冷劑流經蒸發器后再次變成低壓氣體，又重新被吸入壓縮機進行下一次的循環工作。在整個系統中，膨脹閥是控制致冷劑進入蒸發器的機關，致冷劑進入蒸發器太多就不易蒸發而太少冷氣又會不夠，因此膨脹閥是調節中樞。而壓縮機是系統的心臟，系統循環的動力源泉。

盡管汽車空調的空調系統的原理與其它空調系統是相同的，但汽車空調是移動式車載的空調裝置，它與固定式空調系統相比，動轉條件更惡劣，隨汽車行駛的顫振，空調系統的制冷劑比固定式更容易泄漏，空調系統的維修與保養也比固定式頻繁，空調裝置中風路系統在吸入新風時常常會將塵土吸入，堵塞過濾網及蒸發器，在清洗過程中又往往會把制冷劑泄放到大氣中去。造成臭氧層消耗，破壞了環境。

二．汽車空調的組成

汽車空調一般主要由壓縮機、電控離合器、冷凝器、蒸發器、膨脹閥、貯液干燥器、管道、冷凝風扇、真空電磁閥、怠速器和控制系統等組成。汽車空調分高壓管路和低壓管路。高壓側包括壓縮機輸出側、高壓管路、冷凝器、貯液干燥器和液體管路；低壓側包括蒸發器、積累器、回氣管路、壓縮機輸入側和壓縮機機油池。

貯液干燥器——實際上是一個貯存制冷劑及吸收制冷劑水分、雜質的裝置。一方面，它相當于汽車的油箱，為泄露制冷劑多出的空間補充制冷劑。另一方面，它又像空氣濾清器那樣，過濾掉制冷劑中摻雜的雜質。貯液干燥器中還裝有一定的硅膠物質，起到吸收水分的作用。

冷凝器和蒸發器——它們雖然叫法不一樣，但結構類似。它們都是在一排彎繞的管道上布滿散熱用的金屬薄片，以此實現外界空氣與管道內物質的熱交換的裝置。冷凝器的冷凝指的是其管道內的制冷劑散熱從氣態凝成液態。其原理與發動機的散熱水箱相近（區別只在于水箱的水一直是液態而已），所以它經常被安裝在車頭，與水箱一起，共同享受來自前方的習習涼風。總之冷凝器是哪里涼快哪里去，以便其散熱冷凝。蒸發器與冷凝器正好相反，它是制冷劑由液態變成氣態（即蒸發）吸收熱量的場所。

壓縮機——是空調制冷系統的心臟，它是一種使制冷劑在系統內循環的動力源。

管道——由于要注入一定壓力的制冷劑，所以必須采用金屬管道。特別是從壓縮機到冷凝器到制冷劑瓶到膨脹閥這段，由于屬系統的高壓段，所以比其它管道有更高的耐高壓要求。

壓縮機——顧名思義，壓縮機就是起壓縮的作用，它的作用是使制冷劑完成從氣態到液態的轉變過程，達到制冷劑散熱凝露的目的。同時在整個空調系統，壓縮機還是管路內介質運轉的壓力源，沒有它，系統不僅不制冷而且還失去了運行的動力。

壓縮機的分類：

活塞式：活塞式壓縮機的結構酷似發動機，有曲軸、連桿、活塞、氣缸等，但因為它并不產生能量，所以噴油咀、火花塞等就沒有了。長途貨動車或大客車因為空間較大，所以體積較大、損耗較小的活塞式壓縮機常被使用。

斜盤式：一般的轎車、小型商用車所使用的都是斜盤式壓縮機。因為其體積小、質量輕，易于在狹小的發動機室內安裝排布，所以廣為使用。

雖然結構上有很大的區別，但實際上這兩種壓縮機都是把來自發動機轉動的動能轉化成壓縮機內活塞的往復運動，并以此對空調系統的管路形成壓力，達到壓縮制冷劑的目的。

汽車空調不需要如家用空調般每次關機后必須停三幾分鐘再開，實際上車用空調即使在冬天也應每周開啟一下，讓各零件得到潤滑。另外，隔塵網也應注意檢查，如附上太多灰塵則要及時更換。位于車頭的冷凝器在每次洗車時最好用高壓水槍沖洗，以防散熱葉片被雜物（昆蟲、樹葉等）堵塞影響散熱效果。

值得一提的是，壓縮機的旋轉軸是通過磁性離合器及皮帶與發動機曲軸相連取得動力的。為什么要有一個磁性離合器呢？因為當裝在蒸發器出風口的傳感器感知出風的溫度不夠低時，它就會通過電路使壓縮機的磁性離合器閉合，這樣壓縮機隨發動機運轉，實現制冷。而當出風溫度低于設定的溫度，它則控制磁性離合器切離，這樣壓縮機不工作。如果這一控制失靈，那么壓縮機將不斷工作，使蒸發器結冰造成管道壓力超標，最終破壞系統甚至造成損壞。

目前大部分小汽車（主要指民用小車）上用的制冷劑有R-12制冷劑和R -134a 制冷劑兩種。R-12制冷劑是一種普通制冷劑，含有會破壞臭氧層的物質--氟利昂，而且在明火下會生成對人體有害的物質；而R -134a 是一種新型環保制冷劑，具有無毒、無色、不燃不爆、熱穩定性好等性質，更重要的是R -134a 制冷劑不損害臭氧層。

這兩種制冷劑的化學結構互不相同，所以在汽車上是不通用的。而且它們配套使用的制冷劑油也不可互溶。如果加錯制冷劑會令系統損壞，如對膠管的腐蝕等。R 134a 之所以用來替代R12，是因為其熱力性質與R12相似，是一種不含氯的氟利昂，其臭氧破壞系統為零，所以，現在的新車基本都已使用R 134a ，即人們常說的環保制冷劑。

三．汽車空調系統分類（按動力源分）

1．獨立式空調：有專門的動力源（如第二臺內燃機）驅動整個空調系統的運行。一般用于長途貨運、高地板大中巴等車上。獨立式空調由于需要兩臺發動機，燃油消耗高，同時造成較高的成本，并且其維修及維護十分困難，需要十分熟練的發動機維修人員，而且發動機配件不易獲得，尤其是進口發動機；另外設計和安裝更容易導致系統質量問題的發生，而額外的驅動發動機更增加了發生故障的概率。

2．非獨立式空調：直接利用汽車的行駛動力（發動機）來運轉的空調系統。非獨立式空調由主發動機帶動壓縮機運轉，并由電磁離合器進行控制。接通電源時，離合器斷開，壓縮機停機，從而調節冷氣的供給，達到控制車廂內溫度的目的。其優點是結構簡單、便于安裝布置、噪音小。由于需要消耗主發動機10%-15%的動力，直接影響汽車的加速性能和爬坡能力。同時其制冷量受汽車行駛速度影響，如果汽車停止運行，其空調系統也停止運行。盡管如此，非獨立式空調由于其較低的成本（相對獨立式空調），可*的質量，已逐漸成為市場的主導產品。目前，絕大部分轎車、面包車、小巴都使用這種空調。目前非獨立式空調。

四．汽車空調系統特點

(1)空調裝置運行時振動較大

前面已提到汽車空調裝置是移動式車載空調裝置，由于道路不平，汽車在行駛中顛簸振動大，所以裝置中連接管道應采用撓性制冷劑管道。

(2)冷凝器緊靠著發動機的散熱器,所以它的冷凝溫度往往是低高的,所以其運行工況比其它空調裝置惡劣。

(3)汽車空調系統的壓縮機是直接由發動機驅動的，它是通過一個皮帶驅動機構來實現的。當壓縮機不工作時，壓縮機可以與發動機脫開，它是通過一個電子離合器來實現的。空調系統停止工作時，應經常檢查皮帶的松緊，以確定離合器動作是否正確，有時離合器因軸承的損壞而影響壓縮機的軸封，造成壓縮機軸封處制冷劑泄漏。所以要檢查離合器軸承損壞的早期跡象。