Air conditioning piping connects the four major components of the system—the compressor, condenser, evaporator and expansion valve—to form a closed system, within which the refrigerant is stored or circulates. When the air conditioning system is in operation, the refrigerant circulates continuously, exchanging heat with the outside environment to achieve the cooling function. To ensure the refrigerant transfers heat smoothly and efficiently, the routing of the pipework must be well-designed, facilitating both assembly and disassembly, whilst also being easy to manufacture and cost-effective.

Aluminium tubing, rubber hoses and pipe fittings

These three components are joined together to connect the various parts of the air-conditioning system. Aluminium pipes and rubber hoses are joined using a crimping process; however, there may be slight variations in crimping dimensions between different pipe models and those from different manufacturers. Engine vibrations can cause damage to the pipework; the use of flexible hoses for the pipework connecting the compressor’s suction and discharge ports helps to absorb these vibrations, improve the system’s seal integrity and extend the service life of the pipework. Furthermore, some sections of pipework, such as the condenser–evaporator line, may be constructed entirely from aluminium tubing. This is primarily due to the minimal relative movement between the condenser and the evaporator.

If the design leaves little clearance between the pipework and surrounding components, or if they are already in close contact, the use of wear-resistant sleeves such as heat-shrink tubing, corrugated tubing or foam may be considered. If there is little clearance between the air-conditioning pipework and the engine exhaust manifold, thermal insulation measures must be taken, such as wrapping the hose in an aluminium foil heat-insulation sleeve. 

Pipe fittings and O-rings

Pipe fittings are used to connect air-conditioning pipework and the various components of the system. Those commonly used at present include: clamp fittings, threaded fittings and quick-connect fittings.

The function of an O-ring is to seal the pipe joint. The material currently used for O-rings is HNBR.

Pipe clamp

The purpose of pipe clamps is to secure the air-conditioning pipework to the vehicle body, preventing relative movement between the two, thereby avoiding interference between the vibrating pipework and surrounding components, as well as preventing refrigerant leaks at the joints.

In addition to metal pipe clamps, plastic pipe clamps can also be used to secure air conditioning pipework. At present, there is a limited range of plastic pipe clamps used on the S-platform’s air conditioning system; however, the development of plastic pipe clamps may be considered in future, taking into account factors such as new projects and cost reduction.

When using pipe clamps, rubber liners must also be fitted to the inside of the clamps to dampen vibrations and prevent noise caused by direct contact between the aluminium pipe and the clamp.

Low-pressure filling port

Their function is to charge and recover refrigerant, as well as to check the system pressure. The high-pressure charging port is usually fitted on the condenser–evaporator line, although some are fitted on the compressor–condenser line. The low-pressure charging port is fitted on the evaporator–compressor line. The appearance of the charging ports is shown in the figure. Furthermore, the charging ports must be fitted with dust caps. These are generally green in colour (although there is now a requirement to change this to blue) and are made of PP.

Pressure switches/sensors

A pressure switch/sensor is a pressure-detection component that monitors the internal pressure of a system in real time, protecting the air-conditioning system by shutting down the compressor in the event of abnormal pressure, thereby safeguarding the system. It is also used to control the speed of the cooling fan. The pressure switch/sensor is shown in the figure.

Silencer

Where design flaws in an air-conditioning system cause noise in the pipework, silencers may be fitted at the identified source of the noise to eliminate it. Silencers are typically installed on the low-pressure pipework, usually near the compressor’s suction inlet. The exact installation location must be determined through testing. It is preferable to prevent noise from occurring in the first place by optimising the system.

Gas-liquid separator

When an air-conditioning system is incorrectly sized, resulting in liquid refrigerant present in the low-pressure piping, this can cause liquid hammer in the compressor; the use of a gas-liquid separator can protect the compressor from damage. It is fitted on the evaporator–compressor line. This component is now rarely found in modern vehicles, as the problem can be avoided through proper system sizing.

In the case of welded clamp piping, the clamp is welded to the pipe after the pipe has been bent. The head of the clamp is machined, ensuring relatively precise dimensional control. In contrast, for swaged clamp piping, the clamp (which has no head structure) is first slipped onto the pipe, and the pipe is then swaged to secure it firmly to the clamp. The torque applied to this clamp must meet the specified requirements. (Currently, the torque requirement for clamps on ￠12 and ￠16 pipes is 11 N·m, whilst for ￠10 pipes it is 6 N·m.) The pipe ends are then formed using a pipe end forming machine, a grooving machine or similar equipment. The final stage is the pipe bending process.

As piping is subject to the constraints of moulds and machinery during fabrication, we should bear the following points in mind when preparing piping data.

① The bending radii for aluminium tubes are R15/20 (￠10), R20 (￠12) and R25 (￠16). These are generally 1.5 times the outer diameter of the tube.

② The length of the shortest straight section of the pipeline centreline must be greater than 20 mm. This length is primarily limited by two factors:

1) Thickness limitations for pipe bending dies.

2) If the pipe is too short, it may come into contact with the pipe bender whilst being bent, resulting in damage or deformation.

③ The minimum distance L between the cutting point and the crimped pipe along the centreline of the aluminium tube must be greater than 16 mm; there must be no other components in the direction of the crimped pipe that could interfere with the crimping process.

④ The length of the shortest straight section at the end of the flared end is 20 mm. This value varies slightly depending on the pipe diameter. The above values should also be determined with reference to the route of the pipework.

The diagram showing the relationship between pipe bending parameters is as follows:

Pressure switches are classified as either three-position or two-position; the operating principle of a three-position pressure switch is analysed below.

1) When the refrigerant pressure is ≤ 0.12 ± 0.02 MPa, as the elastic force of the diaphragm, disc spring and upper spring exceeds the refrigerant pressure, the high- and low-pressure contacts open (OFF), causing the compressor to stop, thereby providing low-pressure protection.

2) When the refrigerant pressure reaches 0.24 MPa or above—a pressure higher than the spring force of the switch—the spring deflects, causing the high- and low-pressure contacts to close (ON), and the compressor operates normally.

3) When the refrigerant pressure reaches 3.2 MPa or above, it exceeds the elastic force of the diaphragm and the disc spring; the disc spring reverses direction to disconnect the high- and low-pressure contacts, causing the compressor to stop and thereby providing high-pressure protection.

4) Medium-pressure switch. When the refrigerant pressure exceeds 1.6 MPa, the pressure overcomes the diaphragm’s spring force, causing the diaphragm to reverse and push the shaft upwards, thereby closing the speed-change contact for the condenser fan (or radiator fan). The fan then operates at high speed, providing medium-pressure protection. When the pressure drops to 1.25 MPa, the diaphragm returns to its original position, the shaft moves downwards, the contacts open, and the condenser fan operates at low speed.

Air-conditioning ductwork layout

Air conditioning pipework serves to transport refrigerant within an air conditioning system; therefore, a well-designed layout of air conditioning pipework should incorporate the following points:

① The pipework is highly reliable, ensuring that there are no refrigerant leaks.

② Does not affect the cooling performance of the air-conditioning system—keeping the refrigerant temperature rise, pressure drop and compressor oil return rate within appropriate limits.

③ Meets NVH requirements without introducing additional vibration or noise.

④ Meet the requirements for final assembly and after-sales maintenance.

⑤ Cost optimisation.

⑥ The overall appearance should be as aesthetically pleasing as possible.

Below, we shall discuss each of these features in detail from the perspective of pipework layout.

Pipeline reliability

Based on the failure modes observed in the pipework of earlier models, we have broadly identified several main causes of pipework damage:

① Aluminium tubing or rubber hoses are worn down by surrounding components

② Aluminium or rubber hoses break as a result of engine vibrations

③ Damage caused by excessive heat at the hose connection

1) To prevent the pipework from being worn down by surrounding components, a reasonable clearance should be allowed for when routing the pipework. As a motor vehicle is a moving machine when in use, this clearance must account for both static and dynamic clearances. Static clearance refers to the gap between two objects with minimal vibration (as virtually all components vibrate whilst the vehicle is in motion), such as between the headlights and the condenser–evaporator pipework, or between the bodywork and the condenser–evaporator pipework; it is recommended that this clearance be maintained at 15 mm or more. If the clearance is too small or zero and the routing cannot be avoided, the pipes in close proximity should be wrapped in foam, heat-shrink tubing or corrugated tubing.

As the engine vibrates whilst running, dynamic clearances must be taken into account for the two pipes connected to the compressor. For example, the clearance between the compressor’s inlet and outlet hoses and the fan and drive belt. If the clearance is too small, the engine’s forward vibration may cause the air-conditioning hoses to interfere with other components; consequently, the requirements for dynamic clearance are stricter than those for static clearance, and are generally specified as 20 mm or more. As the engine tends to vibrate primarily in a fore-and-aft direction relative to the vehicle, the hoses connected to the compressor should ideally be routed perpendicular to the XZ plane.

When routing the pipework, keep it as far away as possible from the high-temperature components (exhaust pipes) in the front compartment, maintaining a distance of at least 100 mm. If it is genuinely impossible to meet this requirement, the minimum distance must be greater than 40 mm, and the surface must be wrapped in heat-insulating aluminium foil.

Pipeline vibration and noise

Vibration in air-conditioning ductwork is mainly caused by the following factors:

Methods of securing pipework and associated components; 

Selection of hose types for pipework; 

Noise generated by pipework layout.

These three characteristics will be discussed in turn below:

Pipe supports must be fitted with rubber gaskets to prevent rigid connections. If plastic pipe clamps are used, it is also advisable to use gaskets.

All-rubber hoses may be selected for low-pressure piping; as they are relatively flexible, they can effectively absorb vibrations and reduce noise in the pipework.

To minimise noise generated by air-conditioning pipework, the pipework should be laid as short and straight as possible; this also reduces the amount of refrigerant required.

In addition, a silencer can be fitted to the pipework; this will buffer and absorb the pressure pulses generated within the system. The positioning of the silencer is crucial and requires several trials to determine the correct location. The silencer should be installed as close as possible to the compressor end, and there should be at least 25 mm of straight pipework on either side of the silencer.

I. Composition of the Air Conditioning System & Introduction to Components

Composition of the Air Conditioning System:

Automotive air conditioning systems typically comprise the following components: compressor, condenser, receiver-drier, expansion valve, evaporator, blower fan, throttle valve, and ventilation system.

Introduction to Air Conditioning System Components—HVAC Air Conditioning Assembly:

The air conditioning unit employs mode selection dampers to direct cold or warm airflow to specific vents, such as footwell, face, or defrost outlets. Temperature control dampers blend cold and warm air to achieve the desired outlet temperature. The internal/external air mix damper regulates the proportion of cabin and external air, directly influencing temperature, air quality, and defrosting/demisting functionality.

Introduction to Air Conditioning System Components—Condenser:

Function of the condenser: to cool the refrigerant.

The condenser integrated with a dryer, wherein a liquid receiver dryer is installed at the end of the refrigerant circuit within the condenser, facilitates simplified air conditioning system design and enhances the reliability of the refrigeration system.

Introduction to Air Conditioning System Components—Compressor:

The compressor serves as the ‘heart’ of the air conditioning system, analogous to the engine's role in a vehicle—it is the driving unit.
In conventional air conditioning systems, the compressor is driven via an engine belt.
The compressor must exclusively draw in and expel gaseous refrigerant.
Its internal mechanism contains numerous moving parts, necessitating sufficient lubricating oil to lubricate these components.

Introduction to Air Conditioning System Components—Air Conditioning Piping:

The air conditioning piping system comprises key components such as aluminium tubing, flexible hoses, and pipe fittings, which collectively connect all elements of the air conditioning system. Aluminium tubing and flexible hoses are tightly joined via crimping techniques, though minor variations in crimp dimensions may exist between different models and manufacturers. To mitigate potential damage from engine vibration, flexible rubber hoses are employed for the lines connecting the compressor's suction and discharge ports. Their flexible design effectively absorbs vibrations, enhances system sealing integrity, and extends the service life of the piping. Many manufacturers have also developed nylon air conditioning hoses, which are utilised in mass-produced vehicle models.

II. Refrigeration Principles of Air Conditioning Systems

The operational principle of refrigeration systems relies upon the continuous vaporisation and liquefaction of refrigerant. The entire refrigeration cycle comprises four distinct operational stages: compression, condensation and heat release, throttling, and evaporation. During compression, the low-temperature, low-pressure refrigerant gas processed by the evaporator is compressed by the compressor into a high-temperature, high-pressure gas, which is then delivered to the condenser. During the condensation and heat release stage, the high-temperature, high-pressure refrigerant gas gradually condenses into a liquid while releasing heat. The subsequent throttling process, via the expansion valve, transforms the refrigerant from a high-pressure to a low-pressure state. Finally, the evaporation process occurs within the evaporator, where the refrigerant absorbs a significant amount of heat before re-entering the compressor, thereby achieving the cooling of the vehicle's interior.

III. Precautions for Air Conditioning Refrigerant Pipe Assembly

When installing air conditioning pipework and connecting components, the method of fitting and tightening joints is critical.
When removing pipe plugs, first inspect the O-ring for integrity and apply lubricant evenly to its sealing surface. For threaded pipe joints, also apply lubricant evenly to the external threads. When applying lubricant, observe the following points: 
The lubricant applied must be compressor-grade lubricant, PAG or equivalent grade.
Lubricate threaded sections to prevent seizing after tightening.
To prevent moisture absorption, promptly reseal lubricant containers after use.
To maintain internal cleanliness of system components such as piping, remove plugs only immediately prior to installation. Refit promptly; do not leave exposed to air for extended periods.  
Clamp-type joint connection: Insert the lubricated clamp plate's blind hole vertically through the double-ended stud. Simultaneously insert the clamp joint vertically into the corresponding mounting hole. Avoid tilting during insertion to prevent O-ring damage. Once seated with parallel faces, hand-tighten the nut until resistance is encountered. Subsequently, use a torque ratchet or wrench to tighten the bolt to specification, marking the tightened position. The tightening torque for M8 nuts is 15–20 N·m; for expansion valve nuts (M6), it is 6–10 N·m. 
Threaded joint connection. Insert the lubricated sealing ring end into the threaded joint end. Align and insert vertically until the front face of the plug head contacts the threaded joint. Hand-tighten the nut, then secure the threaded joint end with an open-end spanner. Tighten the nut end using a torque wrench, marking the tightened position (see figure below). Tightening torque specifications: High-pressure pipe fitting (M16×1.5 threaded joint): 12–15 N·m Low-pressure pipe fitting (M24×1.5 threaded joint): 30–35 N·m.

Note: When tightening threaded joints, it is essential to use two spanners simultaneously to avoid deformation of the pipework.

Connection of dual clamp joints. First position the end of the high-pressure clamp within the fork slot of the low-pressure clamp. Align and push the compressor interface in parallel. Once the clamps are flattened, inspect the O-ring position for misalignment or extrusion. Hand-tighten the bolts until resistance is encountered, then use a torque ratchet or wrench to tighten to specification, marking the tightened position (see figure below). The tightening torque for the compressor tail bolts (M10×1.25×35) is 20–30 N·m.

Supplementary Notes on Air Conditioning Pipe Installation:

Minor damage to O-rings during pipe installation may compromise sealing integrity, leading to refrigerant leakage.
Following installation, verify that pipes do not interfere with or exhibit free movement relative to surrounding vehicle components. Address any friction or interference promptly through adjustment, and secure pipes prone to free movement with appropriate fastenings.
Moving components such as the engine throttle cable and oil dipstick must never be bundled together with air conditioning piping. This prevents abrasion of the air conditioning lines, which could lead to refrigerant leakage.

The EU’s stringent carbon emission regulations are driving the acceleration of electrification, yet Europe faces a severe shortage of domestic production capacity for batteries, electric drive systems and smart components, coupled with slow technological advancement and a reliance on external supplies. In 2024, China’s exports of automotive components totalled US$93.43 billion, with Europe representing the core growth market.

I.Why accelerate now?

From ‘export products’ to ‘local roots’—the EU’s high tariffs (up to 45.3%), local content requirements (70% local production for non-battery components in electric vehicles), and the New Battery Act (covering carbon footprint, traceability and recycling) have effectively brought an end to the old model of ‘Made in China → Exported to Europe’, with local manufacturing now becoming a prerequisite for market access.

Maturity of China’s Supply Chain + Cost Advantage China possesses the world’s most comprehensive new energy vehicle supply chain, with manufacturing costs 20–30% lower than in Europe. Furthermore, it has established a technological lead in areas such as battery energy density, autonomous driving algorithms and sensors, which aligns with European carmakers’ core objectives of reducing costs and accelerating their transition.

II. From Supporting Roles to Diverse Penetration

• Traditional supply chain exports

From the export of complete vehicles to the subsequent export of components, serving the European factories of Chinese car manufacturers (such as BYD and NIO). This model is characterised by passive supply, low value-added and a focus on trade. In the early stages, small and medium-sized component manufacturers exported items such as wheel rims, interior fittings and standard parts.

• Establishing production capacity

Establishing factories in Europe, recruiting locally and serving local car manufacturers, thereby entering the supply chains of major players such as BMW, Mercedes-Benz, Audi, Volkswagen and Stellantis, and transitioning from a ‘Chinese supplier’ to a ‘local European Tier 1 supplier’.

Using Central and Eastern Europe (Hungary, Slovakia and Poland) as a bridgehead (due to low costs, favourable policies and proximity to Western Europe), whilst establishing R&D centres in Western Europe (Germany and Spain).

• Technology transfer

Technology licensing + joint ventures + solution provision: earn technology fees and long-term royalties without building factories, and secure a position at the high end of the value chain.

• Ecological permeation

With a fully integrated presence spanning R&D, testing, after-sales and local partnerships, we have evolved from a ‘parts supplier’ to a ‘technology partner’, forging close ties with European car manufacturers as they undergo transformation.

BYD’s European headquarters in Hungary (comprising sales, after-sales, R&D and testing) collaborates on research with local universities.

III. Key Challenges

• Compliance barriers

EU REACH, PFAS restrictions and the Battery Regulation: with extremely stringent requirements regarding chemical traceability, carbon footprints and recycling systems, compliance costs for small and medium-sized suppliers are soaring, and they risk being forced out of the market.

Data compliance: Localised storage of autonomous/intelligent driving data and strict privacy protection; algorithms exported overseas must comply with EU regulations.

• Cost and operational barriers

The cost of setting up a factory in Europe is two to three times that in China; labour costs are high, and unit production costs rise by 15–20 per cent, which must be offset through automation and lean manufacturing.

Strong trade unions and strict employment regulations: redundancies are difficult to implement, benefits are generous, and cross-cultural management presents significant challenges.

Domestic giants (Bosch, Continental and ZF) continue to dominate the high-end chassis and traditional powertrain components markets, drawing on a century of technical expertise.

Japanese and South Korean companies (Samsung SDI and LG Energy Solution) have a clear first-mover advantage, and competition in the battery sector is fierce.