Refrigerant Leaks in ACs, Heat Pumps, and Mini Splits

A refrigerant leak in a mini split, heat pump, or air conditioner reduces cooling and heating capacity, raises operating cost, can damage the compressor, and releases potent greenhouse gases into the atmosphere. Refrigerant leaks are also one of the most common causes of AC and heat pump failure we see in New Hampshire homes. Most are preventable through proper installation practices and quality components.

Here is how leaks happen, how we find them, and how A.J. LeBlanc Heating's installation process is designed to prevent them in the first place.

Where refrigerant leaks happen

An AC, heat pump, or mini split is a sealed refrigerant loop. It should never leak. When it does, the leak almost always comes from one of these locations:

• Flare connections at the outdoor unit, indoor head, or service ports (most common on mini splits)
• Brazed joints where copper tubing was soldered (most common on traditional AC systems)
• Schrader valves and service ports (small valves used for charging and service)
• Coil tubing in the indoor evaporator or outdoor condenser (corrosion or formicary corrosion)
• Line set runs where copper tubing has been damaged by movement, vibration, or rodents

Why leaks happen

Common causes:

• Improper flare connections on mini split installations (over- or under-torqued flares, damaged flare faces)
• Vibration over time stressing connections at the outdoor unit
• Formicary corrosion on copper coils, caused by certain VOCs interacting with copper in the presence of moisture (more common in newer high-density coil designs)
• Physical damage from landscaping, snow removal, or rodents chewing on insulation and tubing
• Inadequate brazing technique on field-installed line sets
• Worn Schrader valve cores from repeated service connections

How a refrigerant leak shows up

Symptoms that signal a possible leak:

• Cooling or heating capacity has dropped noticeably
• The system runs longer to reach the setpoint
• Indoor coil ices over in cooling mode
• Outdoor unit ices over more than usual in heating mode
• Electricity bills have crept up without a behavior change
• A hissing sound near the indoor unit, outdoor unit, or line set
• Visible oily residue near a connection (refrigerant oil escapes with the refrigerant)

How we find leaks

A technician with proper instruments can locate most refrigerant leaks during a service call:

• Electronic refrigerant leak detectors sniff for refrigerant molecules and indicate location
• Infrared (IR) leak detectors visualize refrigerant escape against a thermal background, particularly useful for hard-to-reach areas
• UV dye injection tags the refrigerant with a fluorescent dye, then a UV light shows where the dye is escaping
• Bubble leak detector (soap solution) on suspected joints for confirmation
• Pressure decay testing with nitrogen on systems that have been recovered, before recharging

Topping off a leaking system without finding and repairing the leak is a short-term workaround. The refrigerant will leak out again, often more quickly the second time, and the released refrigerant contributes to climate change.

How we prevent leaks during installation

The best leak repair is a leak prevented during install. Our standard installation process is designed around long-term leak-free operation:

Quality flare connections (or no flare connections at all)

For mini split installations, flare connections at the line set are the highest-risk point. Best practices:

• Use a precision flare tool to produce uniform, defect-free flares
• Apply a small amount of refrigerant-compatible thread sealant
• Torque connections to manufacturer specifications
• For applications where flare connections are at high risk, use mechanical leak-prevention fittings or braze the connections instead

Triple evacuation

Before charging, we pull a deep vacuum on the system to remove air, moisture, and any non-condensables that would otherwise circulate inside the loop. The industry-standard triple evacuation process:

1. Pull vacuum to a target deep level (typically below 500 microns)
2. Break vacuum with dry nitrogen
3. Pull vacuum again
4. Break with dry nitrogen again
5. Pull final vacuum to below 300 microns

The final vacuum must hold below 500 microns for at least 10 minutes after disconnecting the vacuum pump. If the pressure rises, there is either a leak or residual moisture. The system is not charged until the vacuum holds.

Nitrogen purge during brazing

When making brazed connections, we purge nitrogen through the tubing during brazing to prevent oxidation scale from forming inside the pipe. Scale particles inside the loop can damage compressor valves and metering devices over time.

Proper line set support and protection

• Line sets are supported to prevent sagging and vibration
• Insulation is continuous (no gaps where rodents can enter)
• Routing avoids sharp bends and physical hazards
• Line covers protect exterior runs from UV and mechanical damage

Why DIY mini split installs frequently leak

Pre-charged DIY mini split kits use flare-style quick-connect fittings instead of brazed connections. These work but are more prone to slow leaks than properly made professional flares. We see DIY systems lose their entire factory charge within a year or two, which then requires an EPA-certified technician to evacuate and recharge (often costing more than the original DIY savings).

Refrigerant changes affect leak handling

Older R-22 systems (production stopped 2020) are increasingly expensive to recharge if they leak. R-410A systems are common today but are being phased out starting in 2025 in favor of R-32 and R-454B. Repairing a leak on an older R-22 system often tips the math toward replacement rather than repair, especially as R-22 stockpile prices climb.

Schedule a leak diagnosis or installation

If your AC, heat pump, or mini split is losing capacity, icing over, or showing other signs of a refrigerant leak, do not just top it off. Contact A.J. LeBlanc Heating for proper diagnosis and repair. Serving New Hampshire families since 1928.

Frequently Asked Questions

Can I top off my own AC if it is low on refrigerant?

No. Federal EPA Section 608 regulations require refrigerant work be performed by a certified technician. More importantly, topping off without finding the leak guarantees the refrigerant will escape again and contribute to atmospheric warming.

Why does my mini split keep losing refrigerant?

Most commonly a slow leak at a flare connection. Less commonly, formicary corrosion in the indoor coil. A technician with proper instruments can identify the leak location.

What is triple evacuation?

An industry-standard installation procedure that pulls vacuum on the system three times with nitrogen purges between, to remove all air and moisture before charging with refrigerant. Required for long-term reliability.

Are refrigerant leaks bad for the environment?

Yes. Older refrigerants like R-22 and R-410A are potent greenhouse gases. R-32 and R-454B (the current replacements) have lower global warming potential but are still regulated. Leak prevention matters.

How much does refrigerant leak repair cost?

Highly variable depending on the leak location and the amount of refrigerant lost. Simple leaks (Schrader valve, easy-access flare) may be a few hundred dollars including recharge. Difficult leaks (coil replacement, hidden line set damage) can run into the thousands.