What is the working principle of an Air conditioning reducing nut?

An air conditioning reducing nut works by mechanically compressing a flared copper pipe end against a tapered sealing seat inside the nut body, creating a leak-free refrigerant connection between two pipes of different diameters. The nut has different thread sizes and bore diameters on each end — one sized for the smaller pipe and one for the larger — allowing it to bridge the diameter gap while simultaneously locking both flared ends in place and sealing them with internal rubber sealing rings. The result is a precisely aligned, pressure-rated mechanical joint that prevents refrigerant leakage and maintains smooth flow through the piping system.

The Mechanical Sealing Process Step by Step

Understanding how the reducing nut achieves its seal clarifies why correct installation technique is essential:

1. Flaring preparation: both copper pipe ends must be flared to the standard 45-degree angle before assembly — the flare creates the conical surface that mates with the internal sealing seat of the nut
2. Sealing ring positioning: refrigerant-resistant nitrile rubber sealing rings are pre-fitted on the inner wall of each bore — these conform precisely to the flared pipe diameter on their respective sides and cannot be removed once vulcanized to the inner surface
3. Thread engagement: as the reducing nut is threaded onto the connection point, the internal tapered seat begins to contact the flared copper pipe end
4. Compression sealing: continued tightening advances the flared pipe end deeper into the tapered seat, compressing the nitrile rubber sealing ring between the copper flare surface and the brass seat — the seal forms through controlled radial and axial compression of the elastomer
5. Final torque and lock: once the specified torque is reached, the nut is fully tightened and both pipe ends are mechanically locked — the joint can withstand operating pressures and temperature cycling without loosening or leaking

Material and Construction: Why Brass Is Used

Air conditioning reducing nuts are manufactured from H62 or H65 brass alloy — a copper-zinc alloy specifically selected for refrigerant piping applications due to its combination of mechanical and chemical properties:

• Corrosion resistance: brass resists the combined chemical environment of refrigerant, compressor oil, and moisture that causes premature corrosion in ferrous metals
• Thermal stability: the brass body maintains dimensional accuracy across the operating temperature range of -30°C to +120°C, preventing joint deformation or seal failure during temperature cycling between compressor shutdown and full-load operation
• Machinability for precision: brass can be precision-turned to the tight dimensional tolerances required for reliable thread engagement and sealing seat geometry — the entire body is manufactured as a single piece through cold heading followed by precision CNC turning
• Compatibility with copper pipe: brass and copper are galvanically compatible — connecting a brass fitting to copper pipe does not create the electrolytic corrosion that would occur with a steel or aluminum fitting

The Role of the Nitrile Rubber Sealing Ring

The sealing ring is the component that provides the actual refrigerant barrier within the reducing nut assembly. Its design and material are critical to long-term leak-free performance:

• Nitrile rubber (NBR) formulation: nitrile rubber has excellent resistance to the mineral and synthetic oils used in compressor lubrication and maintains elasticity across the full operating temperature range of the system
• Vulcanization bonding: the rings are vulcanized (heat-cured) directly to the inner bore wall — this permanent bonding prevents the ring from shifting, falling out during installation, or being accidentally omitted, ensuring sealing integrity is always present when the nut is tightened
• Refrigerant compatibility: the NBR formulation is tested for compatibility with R22, R410A, and R32 refrigerants — the three most widely used refrigerants in residential and commercial air conditioning systems
• Compression recovery: after initial compression during assembly, the elastomer maintains its sealing force over years of service due to the material's long-term compression set resistance

Design Features That Improve Installation Reliability

Beyond the fundamental sealing mechanism, quality reducing nuts incorporate several design features that prevent installation errors and improve on-site efficiency:

Stepped Positioning Mechanism

Select models include an internal stepped recess that physically stops the pipe end at the correct insertion depth — preventing under-insertion that would result in an incomplete seal, and providing tactile confirmation that the pipe is correctly positioned before tightening begins. This quick alignment feature is particularly valuable during maintenance work where installation speed matters and visual access to the joint may be limited.

Anti-Slip Hexagonal Outer Surface

The outer surface of the nut body is machined with a hexagonal profile that fits standard wrench sizes. The flat surfaces of the hexagon provide a positive grip for the wrench, preventing slippage under the high torque required to achieve proper sealing compression. This reduces the risk of wrench slip injuries and surface damage to the fitting during installation.

Coverage of Eight or More Diameter Combinations

A comprehensive range of reducing nuts covers more than eight major pipe diameter combinations, providing solutions for the full range of pipe size transitions encountered in residential and commercial air conditioning work — from small-diameter indoor unit connections through to larger main pipe diameters used in multi-split outdoor units.

Applications Where Reducing Nuts Are Used

About the Manufacturer

Shaoxing DingSen Refrigeration Technology Co., Ltd. was founded in 2008, mainly producing refrigeration accessories and auto air-conditioning accessories. Having been established for more than 10 years, the company has since taken "Honesty and Innovation" as its goal, and "Superb Manufacture, Good Virtue, Serious Attitude, and High Quality" as its business philosophy. Guided by high-tech development, it adheres to a sustainable path of growth focused on quality and benefit.

Through continuous innovation and practice, the company has built a solid quality foundation and a guaranteed reputation in the manufacturing industry. Meanwhile, with efficient and high-quality service and a belief in mutual benefit, the company actively cooperates with businesses from all fields, constantly explores the market, and strives to create a better tomorrow.