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Function and Components of an Air Conditioner (Articles) |
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Michael II  10-03-2007, 17:58 |
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Fundamentals of Climate Technology
Refrigerant Cycle Check refrigerant pressure (R134a) Diagnose with VCDS Fundamentals of HVAC Physical Fundamentals: The four known states of water also exist in the refrigerants of the air conditioning system. 
1 gaseous (not visible) 2 vaporous 3 liquid 4 solid When water is heated in a container (heat absorption), rising water vapor becomes visible. If the vapor is heated further through heat absorption, it becomes visible vapor, which turns into invisible gas. The process is reversible. When you remove the heat content from gaseous water, it first turns into steam, and then into water, and finally into ice.  A-Heat absorption B-Heat release Heat always flows from the warmer substance to the colder substance Every substance consists of a mass of moving molecules. The rapidly moving molecules of a warmer substance transfer some of their energy to the molecules with less heat, which are slower. This slows down the movement of the molecules in the warmer substance and speeds up the movement of the cooler substance. This continues until the molecules of both substances move at the same speed. Then they have the same temperature and no further heat exchange occurs. Pressure and boiling point The boiling point of a liquid, as indicated in the tables, always refers to the atmospheric pressure of 1 bar. If the pressure above a liquid is changed, its boiling point also changes. It is known that, for example, water boils at lower temperatures as the pressure decreases. By examining the vapor pressure curves for water and refrigerant R134a, it can be seen that, for example, at a constant pressure, the vapor turns into liquid (in the condenser) by lowering the temperature, or that, for example, by reducing the pressure, the refrigerant transitions from the liquid to the vapor state. (Condenser).  Vapor Pressure Curve Water A- liquid B- gaseous C- Vapor Pressure Curve Water 1- Pressure above the liquid in bar (absolute) 2- Temperature in °C Vapor Pressure Curve Refrigerant R134a A- liquid B- gaseous D- Vapor Pressure Curve Refrigerant R134a 1- Pressure above the liquid in bar (absolute) 2- Temperature in °C Vapor Pressure Table for Refrigerant R134a: For each refrigerant, the vapor pressure table is known in the literature for refrigeration technicians. From this table, you can determine which vapor pressure is acting above the liquid column in the container, given the container's temperature. Since there is a specific vapor pressure table for each refrigerant, you can determine which refrigerant it is by measuring the pressure and temperature. Note! Absolute pressure of 0 bar corresponds to a perfect vacuum. The normal atmospheric pressure (overpressure) corresponds to 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (indicated by the value -1 bar below 0)
Refrigerant R134a: The evaporation and condensation process is the method used in vehicle air conditioning systems. It involves working with a substance that evaporates and condenses easily, which we call a refrigerant. The refrigerant used is tetrafluoroethane R134a, which boils at -26.5°C under a vapor pressure of 1 bar. Physical properties of refrigerant R134a Chemical formula CH2F-CF3 or CF3-CH2F Chemical name Tetrafluoroethane Boiling point at 1 bar - 26.5 °C Freezing point -101.6 °C Critical temperature 100.6 °C Critical pressure 40.56 bar (absolute) Krit unkt: The critical point (critical temperature and critical pressure) means that there is no separating surface between liquid and gas above this point. A substance is always gaseous above its critical point. At temperatures below the critical point, all types of refrigerants in pressure containers have both a liquid and a gas phase, i.e., there is a gas bubble above the liquid. As long as there is still gas in the container besides the liquid, the pressure depends on the ambient temperature. þ Page * Vapor pressure table Note Refrigerants must not be mixed with each other. Only the refrigerant specified for the particular air conditioning system may be used. Environmental aspects for the refrigerant R134a R134a is a fluorinated hydrocarbon (FKW) and contains no chlorine. R134a has a shorter atmospheric lifetime than the refrigerant R12. R134a does not deplete the ozone layer. The contribution of R134a to the greenhouse effect is 10 times smaller than that of the refrigerant R12. Newer vehicles use the refrigerant R1234yf instead of R134a, which is highly controversial due to the formation of very toxic substances during fires. Currently, work is still being done on air conditioning systems that use the relatively harmless CO2 as a refrigerant. Properties of the refrigerant R134a Trade names and designations The refrigerant R134a is currently available under the following trade names. H-FKW 134a SUVA 134a KLEA 134a Note! Due to the wide selection of different refrigerants, only the refrigerant intended for the specific vehicle should be used. The terms "Frigen" or "Freon" are trade names. These also apply to refrigerants that are not permitted for use in vehicles. Color Refrigerant appears colorless as a vapor and liquid, like water. Gas is invisible. Only the boundary layer between gas and liquid is visible. (Liquid level in the rising tube of the filling cylinder or bubbles in a viewing glass). In a viewing glass, the refrigerant R134a liquid can appear tinted (milky). This opacity is due to partially dissolved refrigerant oil and does not indicate a fault. Vapor Pressure In a partially filled, closed container, vaporous refrigerant evaporates from the surface in an amount that isThe process of converting steam back into liquid is called condensation. This equilibrium state is created under pressure and is often referred to as vapor pressure. Vapor pressure is temperature-dependent. Physical properties of R134a The vapor pressure curves of R134a and other refrigerants are sometimes very similar, therefore, a clear distinction cannot be made solely based on pressure. The lubrication of the compressor in R134a is achieved using special synthetic refrigerant oils, e.g. PAG oils (Polyalkylene glycol oils). Behavior against metals In its pure state, refrigerant R134a is chemically stable and does not attack iron or aluminum. However, contamination of the refrigerant, e.g. with chlorine compounds, leads to the attack of certain metals and plastics. This can lead to blockages, leaks, or deposits on the compressor piston. Critical temperature / critical pressure Up to a gas pressure of 39.5 bar (corresponding to a temperature of 101 °C), the refrigerant R134a remains chemically stable; above this temperature, the refrigerant decomposes (see flammability). Water content Wateris only sparingly soluble in liquid refrigerant. In contrast, refrigerant vapor and water vapor mix in any ratio. In the refrigerant circuit, any existing water is carried along as droplets if the dryer has already absorbed approximately 8 grams of water in its liquid or collection container. This water flows to the nozzle of the expansion valve or the throttle and turns into ice. The air conditioner stops cooling. Water damages the air conditioner because acids are formed under high pressures and temperatures in combination with other contaminants. Flammability Refrigerant is non-flammable. In fact, it has fire-retardant or fire-extinguishing properties. Refrigerant is decomposed by flames and hot surfaces. Refrigerant is also split by UV light (occurs during electrical welding). This produces toxic byproducts, which must not be inhaled. However, irritation of the mucous membranes provides sufficient and timely warning. Refrigerant charge In a container, there must be a vapor space for the liquid space. As the temperature increases, the liquid expands. The vapor-filled space becomes smaller. At a certain point, there will only be liquid in the container. Subsequently, only a slight temperature increase is sufficient, and very high pressures develop in the container because the liquid wants to expand further, but there is no more space available. The resulting forces are large enough to rupture the container. In order to prevent containers from being overfilled, the Pressure Gas Ordinance specifies how many kilograms of refrigerant per liter of internal volume of the container may be filled. This "fill factor" multiplied by the internal volume gives the permissible fill volume. For refrigerants used in vehicles, it is 1.15 kg/l. Proof of leaks The refrigerant circuit can become leaky due to external damage, for example. The detection of small leaks can be achieved due to the small amount of refrigerant that leaks, for example, by using an electronically operated leak detector. With this device, leaks with less than 5 grams of refrigerant loss per year can be detected. (For different refrigerants, leak detectors that are designed for the composition of the specific refrigerant should be used. For example, leak detectors for R12 refrigerant are not suitable for R134a refrigerant, as the R134a refrigerant does not contain chlorine atoms, so these leak detectors will not respond). Refrigerant machine oil Refrigerant machine oil mixes (approximately 20-40%, depending on the compressor type and refrigerant amount) with theMiddle-aged, constantly circulating in a cycle and lubricating moving parts. When used with R134a air conditioning systems, special synthetic refrigerating machine oils, such as Poly-Alkylene Glycol (PAG) oil, are used. This is necessary because, for example, mineral oil does not mix with R134a. Furthermore, the materials of the R134a air conditioning system could be damaged if the mixture flows under pressure and at high temperatures through the refrigerant cycle, or if the lubricating film in the compressor breaks down. The use of non-approved oils can lead to the failure of the air conditioning system, therefore only approved oils can be filled. Properties of the Refrigerant Oil The most important properties are high solubility with refrigerant, good lubricating properties, acid-free and very low water content. For this reason, only very specific oils can be used; a list of approved refrigerant oils and filling quantities can be found in the vehicle-specific repair manual. PAG oils suitable for refrigerant R134a are highly hygroscopic and cannot be mixed with other oils. Therefore, immediately reseal the containers after opening to protect against moisture. Refrigerant oil degrades due to moisture and acids, becomes dark, viscous, and aggressive towards metals. Note! For refrigerant circuits with refrigerant R134a Only the oil specifically approved for the compressor may be used. Filling volumes see the vehicle-specific repair manual. Due to its chemical properties, the refrigerant oil must not be disposed of together with engine oil or gear oil. Comfort One of the basic prerequisites for concentrated and safe driving is the feeling of comfort in the vehicle interior. This comfort is only possible through the use of an air conditioning system, especially at warm temperatures and high humidity. Of course, open windows, a sunroof, or increased airflow can also contribute to comfort, however, there are disadvantages in the vehicle interior, e.g.: Additional noise, drafts, exhaust fumes, unfiltered entry of pollen and dust (unpleasant for allergy sufferers) With a regulated air conditioning system in combination with a well-designed heating and ventilation system, the feeling of well-being and comfort can be created by controlling the interior temperature, humidity, and air movement, according to the external conditions, both for stationary and moving vehicles. Environmental aspects Since approximately 1992, the KConversion of new car air conditioning systems to the refrigerant R134a. This refrigerant does not contain chlorine and is therefore ozone-friendly. Until approximately 1992, air conditioning systems were equipped with the refrigerant R12. This CFC has a high ozone depletion potential due to its chlorine atoms and also has the potential to enhance the greenhouse effect. Programs are being offered to convert existing air conditioning systems that are filled with the ozone-damaging substance R12. For environmental protection, no refrigerants may be released into the atmosphere. How air conditioning systems work The temperature in the passenger compartment is regulated by radiant heat through the windows and by transitional heat through meta Certainly. However, to ensure comfortable temperatures for passengers on very hot days, a portion of the existing heat must be removed. Since heat spreads towards cooler temperatures, a device is installed in the passenger compartment that generates low temperatures. This device continuously evaporates a refrigerant. The heat required for this is extracted from the air flowing through the evaporator. The refrigerant, now carrying the absorbed heat, is pumped by the compressor. Through the compression work of the compressor, the heat content and temperature of the refrigerant increase. She is now significantly higher than the ambient air temperature. The highly heated refrigerant flows with its heat content to the condenser. There, the refrigerant releases the heat to the ambient air via the condenser due to the temperature difference between the refrigerant and the ambient air. Therefore, the refrigerant is a heat transfer medium. Since it is needed again, it flows back to the evaporator. This is why the basic principle of all air conditioning systems is a refrigerant cycle. Differences arise in the composition of aggregates. Product properties: The refrigerant used in automotive air conditioning belongs to the new generation of refrigerants based on chlorine-free, partially fluorinated hydrocarbons (H-FKW, R134a). In terms of their physical behavior, these are liquefied refrigerants under pressure. They are subject to the Pressure Equipment Directive and can only be filled into approved and marked pressure gas containers. Certain conditions apply for the safe and proper use, which must be observed. Handling of refrigerants! If refrigerant containers are opened, then The contents can emerge as a liquid or vapor. This process is more intense the higher the pressure in the container. The pressure level depends on two conditions: Which type of refrigerant is in the container. It is important to note that the lower the boiling point, the higher the pressure. The temperature. It is important to note that the higher the temperature, the higher the pressure. Do not open containers containing refrigerant. Wear safety glasses! Put on safety glasses. This prevents refrigerant from entering the eyes and potentially causing serious damage from frostbite. Wear protective gloves and an apron! Refrigerants effectively dissolve fats and oils. By removing the protective fat film, they thus come into contact with the skin. However, the exposed skin is sensitive to cold and germs. Do not apply liquid cooling agent to the skin! The cooling agent removes heat from the surrounding environment. Even if it's the skin. Very low temperatures can be achieved in this way. The result is local frostbite (boiling point of R134a -26.5°C at ambient pressure). Do not inhale cooling agent vapors in high concentrations! Escaping cooling agent vapors mix with the surrounding air and displace the oxygen needed for breathing. Absolute no smoking! Cooling agents can decompose in cigarette smoke. The resulting substances are toxic and must not be inhaled. Welding and soldering on refrigeration systems! Before welding and soldering on vehicles (in the vicinity of air conditioning components), the refrigerant must be evacuated and any remaining residue must be removed by blowing with nitrogen. The decomposition products that arise from the refrigerant due to heat are not only toxic but also highly corrosive, so that pipelines and system components can be damaged. These are essentially fluorohydrocarbons. Pungent odor! If there is a pungent odor, the aforementioned decomposition products have already formed. It is absolutely necessary to avoid inhaling these substances, as otherwise damage to the respiratory system, lungs, and other organs could result. Note! Damaged or leaking parts of the air conditioning system must not be repaired by welding or soldering; they must be replaced. When blowing parts with compressed air and nitrogen, the gas mixture that escapes from the parts must always be sucked away using appropriate extraction systems (workshop exhaust system). After completing maintenance work, screw closure caps (with seals) onto all connections with valves and service connections. Starting up the air conditioning system. Pay attention to the filling volumes Do not refill refrigerant, remove existing refrigerant and refill the system. Before starting the air conditioning system after refilling: - Manually rotate the compressor via the clutch or pulley of the magnetic clutch approximately 10 times. - Start the motor with the compressor switched off/control valve -N280-. - After the motor's idle speed has stabilized, turn on the compressor and operate it with idle speed and maximum cooling capacity for at least 10 minutes. General Information about the Refrigerant Cycle Components of the Refrigerant Cycle Distribution of the Components of the Refrigerant Cycle and Their Influence on the High and Low Pressure SidesOn the high-pressure side, these are the condenser, the liquid reservoir, and the throttling valve or expansion valve, which separates the HD-liquid side and the ND-liquid side. High pressure is created because the throttling valve or expansion valve creates a restriction, and the refrigerant becomes stagnant, which leads to a pressure and temperature increase.Excessive pressure occurs if there is too much refrigerant, the condenser is dirty, the fan for the radiator is defective, there is a blockage in the system, or there is moisture in the refrigerant. Refrigeration cycle (Freezing of the evaporator) is present. On the low-pressure side, there is the evaporator, temperature sensor and evaporator, and as a separation from the HD side and the ND side, the compressor. Pressure drop in the system can be caused by refrigerant loss, throttling, or expansion valve (no restriction), compressor failure, or evaporator freezing. Compressor: The compressor is driven by a V-belt from the vehicle engine. Compressor with magnetic clutch: An electromagnetic clutch mounted on the compressor creates the power transmission between the pulley and the compressor crankshaft when the air conditioning is turned on. Compressor without magnetic clutch: A Compressor pulley-mounted overcurrent protection device trips when the compressor is running too hard and protects the belt drive from overload. The compressor sucks refrigerant gas from the evaporator, compresses it, and then sends it on to the condenser.  The compressor contains refrigerant oil, which is mixable with R134a refrigerant at all temperatures. The factory label indicates for which refrigerant the compressor is designed. A control valve regulates the pressure on the low-pressure side within the specified target range (control characteristic). In compressors without a magnetic coupling, a control valve is controlled from the outside. In compressors without a magnetic coupling, the motor may only be started when the refrigerant circuit is completely assembled. To prevent damage to the compressor when the refrigerant circuit is empty, the magnetic coupling is switched off, the control valve N280 is no longer controlled, and the compressor runs at idle with the motor In a compressor without a magnetic coupling, when the refrigerant circuit is empty, it is switched over to internal lubrication via a valve. Overload fuse trips in a difficult-running compressor protects the belt drive from overload. The compressor draws refrigerant gas from the evaporator, compresses it, and then passes it on to the condenser. Condenser: The condenser dissipates heat from the compressed refrigerant gas to the ambient air. In this process, refrigerant gas condenses into a liquid.  Evaporator: The liquid refrigerant evaporates in the evaporator tubes. The heat required for this is extracted from the air flowing past the evaporator fins. The air cools down. The refrigerant evaporates and is sucked in with the heat absorbed by the compressor. A defined amount of refrigerant is supplied to the evaporator via a throttling valve or expansion valve. In systems with an expansion valve, the flow rate is regulated so that only gaseous refrigerant exits at the outlet of the evaporator.  Sight glass: Not used in R134a systems, as it is not suitable for R134a. If a sight glass is present in systems that have been converted from R12 to R134a (retrofit), the mixture of refrigerant R134a and refrigerant oil in the sight glass may appear milky, even though the refrigerant is transparent. <img s rc="/Img2_4.JPG" alt="" width="552" height="453" class="responsive"> Collection tank: In order for the compressor to only suck in gaseous refrigerant, the collection tank captures the mixturecoming from the evaporator of steam and gas. The gaseous refrigerant is extracted from the steam. The refrigerant circulating in the cycle does not remain in the collection tank, as there is an oil suction hole. Moisture that has entered the refrigerant cycle during assembly is captured by a filter (dry bag or cartridge) in the tank. Gaseous refrigerant with oil is sucked in by the compressor.  Drossel: The expansion valve creates a restriction. This restriction restricts the flow and thereby separates the refrigerant circuit into high-pressure side and low-pressure side. Before the expansion valve, the refrigerant is at high pressure and warm. After the expansion valve, the refrigerant is at low pressure and cold. Before the restriction, there is a filter to prevent dirt, and after the restriction, there is a spray nozzle to atomize the refrigerant before it reaches the evaporator. Arrow A on the expansion valve points to the evaporator. This must be replaced after each opening of the circuit.  Liquid reservoir: The liquid reservoir collects the liquid droplets and then leads it continuously to the expansion valve. Moisture, , which has entered the refrigerant circuit during assembly, is collected in the liquid reservoir by a drier. Replace the liquid reservoir if the refrigerant circuit has been open for a long time and moisture has entered. Always replace the liquid reservoir or collection tank when changing refrigerant. The dry bag or cartridge becomes saturated with moisture after a short time in an open liquid reservoir and becomes unusable.  Expansion valve: The expansion valve Atomized refrigerant and regulates the flow rate so that the steam becomes gaseous only at the outlet of the evaporator, depending on the heat transfer.  O-Ring Seals: These rings seal the connection points between the individual components of the refrigerant circuit. Only O-rings that are resistant to refrigerants R134a and associated refrigerant oils may be used. Basically, use only once. Wet with refrigerant oil before installation. Refrigerant Circuit Pipes and Hoses: The mixture of refrigerant oil and refrigerant R134a attacks certain MMaterials (e.g., copper) and alloys, and dissolves certain types of tubing. The pipes and tubing are held together by screwing or using special connectors. When screwing, pay attention to the specified torque values, and when using connectors, use the specified unlocking tools. Overpressure relief valve: The overpressure relief valve is mounted on the compressor or liquid tank. At a pressure of approximately 38 bar, the valve opens and closes when the pressure drops (approximately 30 bar). The refrigerant does not completely empty. Depending on the design, a transparent plastic disc may be attached, which breaks away when the valve opens.Correct.  Refrigerant cycle with expansion valve and a condenser.  1- Condenser 2- Expansion valve 3- Valve for suction, filling and measurement 4- Sight glass not installed in R134a circuits, except for retrofits Circuits 5- Liquid reservoir with drier 6- Condenser 7- Compressor Note! Arrows indicate the direction of refrigerant flow. Refrigerant cycle with expansion valve and two condensers.  1- Condenser 2- Expansion valve 3- Valve for suction, filling and measuring 4- Sight glass not installed in R134a circuits, except for retrofit Circuits 5- Liquid reservoir with desiccant 6- Condenser 7- Compressor 8- Magnetic valve for refrigerant circuit 9- Expansion valve 10- Second evaporator Refrigerant circuit with throttling and collection tank.  1- Compressor 2- Condenser 3- Throttling valve 4- Evaporator 5- Collection tank Check pressure in the refrigerant circuit (R134a, with service station) and function Note The air conditioning system works correctly when the power supply current on the control panel isTemperature of 7°C or lower exit. Testing Requirements The cooler and condenser are clean (if necessary, verschandeln them). The thermal insulation on the expansion valve is in good condition and correctly mounted. The V-ribbed belt is in good condition and correctly tensioned. / The belts for the compressor and three-phase generator are in good condition and correctly tensioned. All air guides, covers, and seals are in good condition and correctly mounted. The troubleshooting of the electrical system and the vacuum system did not reveal any errors. The self-diagnosis of the air conditioning system does not reveal any errors; no compressor shutdown condition is indicated in the measurement block (only for vehicles with self-diagnosis "air conditioning"). The LuThe airflow through the dust and pollen filter is not affected by contamination. The air conditioning unit does not draw in any secondary air at the highest fresh air fan speed. The evaporator and heater do not draw in any secondary air at the highest fresh air fan speed. The air directing flaps in the air conditioning unit, the heater, and the evaporator reach their final position. * The fresh air intake ducts under the hood and in the passenger compartment, and the associated water drainage valves, are in good condition. The engine is at operating temperature. The vehicle is not exposed to direct sunlight. The ambient temperature is greater than 15°C. All control panel switches are open. When the engine is running and set to maximum cooling Setting for air conditioning system: Does the fan (do the fans) run for refrigerant -V7- (at least at level 1)? Does the fresh air blower V2- run at maximum speed? Does the recirculating/fresh air valve switch to "recirculating mode" and closes the static pressure valve and opens the recirculating valve (within 1 minute after starting the vehicle)? Note In certain configurations, the fan is only switched on after the pressure in the refrigerant circuit has exceeded a specified value.
Note The temperature of the components of the refrigeration cycle must be equal to the ambient temperature If individual components of the refrigeration cycle are warmer or colder, the pressure will deviate from the values in the table Absolute pressure corresponds to 0 bar, which is a perfect vacuum. The normal ambient pressure (overpressure) corresponds to 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of 1 bar (indicated by the value -1 bar below 0) In vehicles with high-pressure sensors G65, where the measured pressure is displayed in the measurement block, does the measured pressure match? The pressure in the refrigerant circuit is lower than indicated in the table. Insufficient refrigerant in the circuit. - Search for leaks in the refrigerant circuit using a leak detector. - Check the overpressure relief valve. Note! Has the overpressure relief valve blown? - Check the operation of the cooling fan. - Check the refrigerant lines and refrigerant hoses for cross-sectional narrowing due to small bending radii. - Inspect refrigerant lines and refrigerant hoses for external damage. - If no defects are found, blow the refrigerant circuit with compressed air and nitrogen, and replace the filter drier. The pressure in the refrigerant circuit is within the specified range or higher. - Start the motor. - Set the air conditioner to maximum cooling capacity. Note! - To connect the service station, the low-pressure switch was removed, and the electrical connections in the associated connector were bridged for pressure measurement. The compressor is driven by the motor via the magnetic clutch. The control valve N280 for the compressor is controlled by the air conditioner control unit. Compressor not driven by the engine while running or the control valve not actuated: - Determine the cause, e.g., by querying the climate control's error memory and eliminating it - Observe the test conditions - Check the power supply for the magnetic clutch N25, if it is OK, repair the magnetic clutch - Check the actuation of the control valve N280 Check pressures in vehicles with throttle and reservoir (with internally controlled compressor) Note Observe the test conditions - Bring the engine speed to 2000/min. - Observe the pressure gauge Note Switch pressures for the switches in the refrigerant circuit are vehicle-specific. The connection with the valve for the Low-pressure switches or on the evaporator should only be used on vehicles without a service connection on the low-pressure side and with an inaccessible connection on the compressor or reservoir (measurement accuracy). This only applies to specific vehicles. Target values: High-pressure side: From the outlet pressure (when connecting the gauges) to a maximum of 20 bar overpressure. Low-pressure side: From the outlet pressure (when connecting the gauges) to the value on the diagram.  A- High pressure (measured at the service connection) in bar overpressure. B- Low pressure (measured at the connection with a valve on the compressor or reservoir) inbar Overpressure. C- Acceptable Tolerance Range. D- Low Pressure (measured at the connection with the low-pressure switch or at the service connection) in bar Overpressure. E- Acceptable Tolerance Range.
The average value in the cycle is within limits. On the Audi 100, Audi A6 (up to and including the 1997 model year) and Audi V8, the compressor can be switched off from the control and display unit (if the temperature in the fresh air blower falls below -3 °C). Check vehicles with expansion valve and reservoir (with internally controlled compressor).  A- High pressure in bar Overpressure. B- Low pressure in bar Overpressure. C- Permissible tolerance range.
Testing requirements: The radiator and condenser are clean, if necessary, verschandeln with a cleaning spray. The V-belt for the compressor and three-phase generator is correctly tensioned. All air ducts, covers and seals are in good condition. and properly assembled. The flaps have reached their final position. The motor is warmed up. The evaporator and heater do not draw in any additional air (at the highest fresh air fan speed). With the engine running and the air conditioning set to maximum cooling performance - the fresh air fan is running. - the coolant fan is running or switched on. - the recirculation/fresh air flap is in the "recirculation" position. Ambient temperature greater than 15 °C. The evaporator temperature switch E33 is properly assembled and its switch temperatures are correct.
- Search for leaks using a leak detector. - Check the overpressure relief valve, and verify the control for the fans for refrigerant according to the wiring diagram. Inspect refrigerant lines and refrigerant hoses for too small bending radii (cross-section reduction) or external damage. If no fault is found, flush the refrigerant circuit and replace the filter drier. The pressure in the refrigerant circuit is as indicated in the table or higher: - Start the motor. - Set the air conditioner to maximum cooling performance. - Open the doors. - Open the air outlets in the control panel. - The compressor is in the ls Keilrippenriemen über die Magnetkupplung Motor-driven. Note: If the compressor is not running, check the power supply for the N25 magnetic clutch according to the wiring diagram, if the power supply is normal, repair the magnetic clutch. If the compressor is running, check the refrigerant circuit: - Bring the engine speed to 2000 RPM. - Observe the pressure gauge battery: Nominal values: High-pressure side: pressure increasing from the pressure at a standstill up to a maximum of 20 bar overpressure. Low-pressure side: pressure decreasing from the pressure at a standstill to 1.3 bar overpressure. Check the pressure in vehicles with a throttle, accumulator, and control valve N280 (with externally controlled compressor). Nominal values: High-pressure side: From the output (When connecting the pressure gauges) increase to a maximum pressure of 20 bar. Low-pressure side: Decreasing from the initial pressure (when connecting the gauges) to the value on the diagram.  A-Low-pressure (measured at the service connection) in absolute pressure B-Control current for the N280 control valve Note: The pressure on the low-pressure side can increase to a maximum of 29 bar under unfavorable conditions (very high ambient temperatures, high humidity). The control current -B- is displayed in the measuring block. The high pressure is displayed in the measuring block. The low pressure adjusts depending on the control current for The control valve N280 must be installed within the performance range of the compressor, within the specified tolerance. Under unfavorable conditions (very high ambient temperatures, high humidity), the performance may not always be sufficient to achieve the specified value. The operating current for the control valve must be greater than 0.3 A to ensure safe operation of the control valve. When setting the "maximum cooling capacity", the control current is regulated to approximately 0.8 A (displayed in the measurement block).
VCDS from Dieselschrauber is an indispensable tool for troubleshooting. In the air conditioning system's fault memory and the data blocks, many helpful information for troubleshooting and problem solving can be obtained. The following simple tests can be performed to identify errors: 1) Basic inspection of the climate control system in the engine compartment [08-Climate] using VCDS. - Is the initial setup completely based on previous work? - Is the tax device properly coded? - Are the correct parts/control units installed? - Understand and troubleshoot errors in the fault memory, and then search for the corresponding error codes on our pages / on the web. 2) The data blocks of the climate control device are functioning correctly: - Compressor shutdown code - Coolant Pressure (G65) - Outdoor temperature (filtered/unfiltered) - Evaporation temperature - Blowing temperatures 3) Check the current coolant pressure - Use a suitable pressure gauge to accurately measure the actual coolant pressure, as the G65 may be faulty. Caution: Coolant can cause serious injuries. Use only appropriate tools and follow the manufacturer's safety instructions! 4) Check the function of the cooling fans - In many vehicles, the fans on the radiator can be controlled via a control element in the engine control unit [01 - Engine]. - Also, bitte auch den Fehlerspeicher des [01 - Motor] überprüfen! 5) Look for damage: - Is the compressor running? Also, the wave? - Check the wiring and connections! - Check for leaks in the air conditioning system's pipes/condenser. Additional Notes and Tips: For some vehicles from the 2006-2009 model years, it may be necessary to reset the temperature sensor(s) after they have been replaced: Let the vehicle run for 20 minutes in a stationary position. If the shutdown code from the compressor [0] is N280, check the N280 valve, which controls the amount of coolant that the compressor pumps through the system. The signal for N280 can, for example, be tested using a test lamp (as a replacement for N280). Compressor Shutdown Codes: (Check your repair manual or Measuring Value Block pop-up) - 0 = Compressor ON - 1 = Compressor OFF: Coolant pressure too high (> 32 bar) - 2 = Compressor OFF: Basic settings not performed - 3 = Compressor OFF: Refrigerant pressure too low (< 2.0 bar) - 5 = Compressor OFF: Engine start detected - 6 = Compressor OFF: ECON mode active - 7 = Compressor OFF: A/C System / Fan OFF - 8 = Compressor OFF: Outdoor temperature too low (< 3.0 °C) - 10 = Compressor OFF: Battery voltage too low (<10> 118 °C) - 12 = Compressor OFF: Engine control unit has requested shutdown (e.g., when stopping) - 13 = Compressor OFF: Voltage too high (> 17 V) - 14 = Compressor OFF: Evaporator temperature too low - 16 = Compressor OFF: Compressor control faulty - 17 = Compressor OFF: No or faulty signal from the pressure sensor - 18 = Compressor OFF: Deactivation due to vehicle speed - 19 = Compressor OFF: Shutdown requested by central electrical system (load management) Newer air conditioners use a pressure sensor (G65) instead of a pressure switch (F129). This sends the print via a PWM signal (Pin 1: Ground, Pin 2: Signal) to the climate control unit. Last edited on 15-04-2024, 19:30, edited 6 times in total. |
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| Ratings - Function and Components of an Air Conditioner | |
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