Do Dry or Wet Copper Flares Leak High Pressure Refrigerant on Ductless Mini-Split Units?

When it comes to installing ductless mini-split units, one of the critical considerations is whether to use dry or wet copper flares. The decision can significantly impact the potential for refrigerant leaks, which is a common issue in mini-split installations. In this article, we will explore the experiment conducted to determine if dry flare joints will leak compared to wet flare joints under high pressure.

The Experiment

Technicians often face the decision of assembling flares completely dry or applying a small amount of nylog or refrigerant oil on the flare face and the flare adapter before tightening them down. To address this, an experiment was conducted using two sets of flares: one set was wet with a little bit of nylog on the flare face, and the other set was left dry. The primary objective was to run a pressure test to identify any potential leaks.

Flare Preparation

The experiment began with the preparation of copper tubes by cutting them into small sections and deburring the ends to ensure no shards were present. The copper tubes were then flared using an eccentric flaring tool, and the resulting flares were examined to ensure they were well-formed and free from imperfections.

Pressure Testing and Leak Detection

The experiment emphasized the importance of pressure testing before vacuuming and adding refrigerant to the system. It was highlighted that pressure testing is crucial for identifying leaks at flare joints, ensuring that the system is free from water, air, and nitrogen. The use of a digital gauge set for pressure testing was recommended, as it allows for quick detection of incremental changes.

Dry vs. Wet Flares

The experiment’s findings revealed that both dry and wet flares were capable of holding high pressure. It was noted that the application of nylog on flare faces could help fill any minor imperfections and enhance the seal. However, the long-term effectiveness of wet flares in preventing leaks over time was left open for discussion, inviting input from industry professionals based on their experiences.

Best Practices for Flare Joints

The article stressed the importance of torquing flare joints to the manufacturer’s specifications and conducting thorough leak checks using a non-corrosive bubble leak detector. It was emphasized that even a tiny leak in a flare joint could lead to refrigerant loss over time, impacting the system’s performance. Therefore, proper installation, torque values, and leak checking were highlighted as crucial steps in preventing refrigerant leaks in mini-split systems.


In conclusion, the experiment demonstrated that both dry and wet flares have the potential to hold high pressure, with the application of nylog offering potential benefits in sealing minor imperfections. However, the long-term effectiveness of wet flares in preventing leaks requires further industry input. The article underscored the significance of following manufacturer specifications, conducting thorough leak checks, and using digital gauge sets for pressure testing to ensure the integrity of flare joints in mini-split installations.

By considering the insights from this experiment and adhering to best practices, HVAC technicians can make informed decisions regarding the use of dry or wet copper flares, ultimately contributing to the reliability and performance of ductless mini-split units.

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