How to Find a Refrigerant Leak in an Air Conditioner

What you're seeing

• The house won't cool down and the supply air feels barely cool.
• Ice on the suction line or the indoor coil, especially after a long run time.
• Oily residue on a joint, valve, or coil. Refrigerant carries oil with it, so oil marks the spot.
• A hissing or bubbling sound near the indoor or outdoor unit.

How to track it down

Work through these in order, or follow along in the video above. Each step rules something out before you spend money on parts.

1. Rule out airflow first

   A dirty filter or a blower that isn't moving enough air can freeze a coil and look just like low charge. Check airflow before anyone touches the refrigerant.

2. Confirm it's actually low

   A tech reads superheat and subcooling against the metering device. Low charge usually shows high superheat and low subcooling. Guessing from suction pressure alone gets people in trouble.

3. Check the usual suspects

   Schrader valve cores and caps, flare nuts on mini splits, service valves, and brazed joints. Then the coils themselves. Evaporator coils are one of the most common leak points.

4. Use the right detector

   An electronic leak detector narrows it down, and bubble solution pins it down. On hard-to-find leaks, recover the charge and pressure test with dry nitrogen so you can hear and bubble it at higher pressure.

5. Repair, vacuum, recharge

   Fix the leak, pull a deep vacuum, then weigh in the charge or charge by the manufacturer's method. Skipping the vacuum leaves moisture in the system.

If you're a homeowner

Handling refrigerant legally requires EPA Section 608 certification, so this one is for a licensed tech. What you can do: change the filter, note if you see ice, and turn the system off if the coil is frozen so it can thaw. Ask your tech where the leak is, not just how much refrigerant it took.