One-sentence answer: Automotive air-conditioning pipe joints bear pressure through crimping, brazing and quick-connect structures. Refrigerant molecules are small, and the requirements on sealing faces are higher than those for water and air. A micro-leak at a joint causes slow refrigerant loss and compressor oil starvation. Using the CTS Sentinel A28 differential pressure leak detector to compare a master part with the part under test enables stable judgment on small-volume workpieces such as joints, making it suitable for 100% inspection in batches at air-conditioning pipe plants.
Refrigerant molecules are small and highly permeable. A joint that passes a hydrostatic test may still slowly seep under refrigerant conditions, so the acceptance criteria must be stricter than for general air tightness parts.
Insufficient crimping of an aluminum pipe means the sealing faces do not fit closely enough, while excessive crimping damages the pipe wall and creates stress concentration. Wall thickness tolerances within the same batch of pipe also cause the process window to drift.
Cold solder joints, lack of fusion and residual oxide scale on the inner wall at the weld will develop into leak paths under pressure cycling, and appearance inspection cannot reveal any of this.
During assembly, a scratched or missing O-ring, or a retaining ring that is not fully seated, will seep under high-temperature and vibration conditions, so quantitative interception is needed at the factory exit stage.
Sealing locations:
Consequences of leakage: slow refrigerant loss, degraded air-conditioning cooling capacity, and compressor wear or even seizure due to oil starvation. At the same time, refrigerant emission involves environmental regulations and OEM requirements on leak rate, making it a regulatory item rather than merely an experience item.
Air-conditioning pipe joints are small-volume, high-cycle, high-volume workpieces, and the workshop temperature at pipe plants fluctuates noticeably:
Dry air or nitrogen is usually used, not refrigerant. Air testing is safe, low-cost and fast on the production line, and its leak judgment capability is sufficient to screen out process defects. Refrigerant-related performance verification falls under the scope of complete-machine or bench testing, which is a different matter from 100% inspection on the production line.
Helium testing has high sensitivity but requires a vacuum chamber and helium recovery. Equipment and operating costs are high and the cycle time is slow, making it more suitable for R&D verification or sampling inspection of high-value parts. Air-conditioning pipe parts are large in quantity and relatively low in unit price, so air differential pressure testing is more commonly used for 100% inspection on the production line, achieving a balance between cost and judgment capability.
Crimp first, then perform the air tightness test. Crimping is the key process that determines the fit state of the sealing faces, and only when testing is placed after it can the finished product state be truly reflected. If testing is moved earlier, problems found cannot be attributed to crimping parameters, and the value of guiding the process is lost.
For sealing tests of automotive air-conditioning pipe joints, the key is that small-volume parts also need a stable judgment baseline. The differential pressure comparison structure of the CTS Sentinel A28 maintains stable readings under temperature differences. Combined with plugging fixtures for a range of pipe diameters and 32 test programs, it is suited to batch 100% inspection and traceability for multiple pipe numbers at air-conditioning pipe plants.
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