AC Diagnostics & Repair

Step-by-Step Copper Coil Leak Detection & Nitrogen Pressure Testing

Published on 2026-06-15 · 6 min read · By ACServiceOS Team

One of the most frustrating experiences for a customer is paying for a gas refill, only for the cooling to vanish again 2 weeks later. Professional leak detection with dry nitrogen is non-negotiable.

Technician using nitrogen cylinder and soap bubble test to locate micro-leak in cooling coil

Why You Must NEVER Use Oxygen or Compressed Air for Pressure Testing

Never use oxygen (causes catastrophic explosion when mixed with compressor oil under pressure) or an air compressor (injects moisture that ruins inverter POE oil). Strictly use pure dry nitrogen gas with a certified pressure regulator.

Pressurizing the System to 300-350 PSI

Connect the nitrogen cylinder through the high-pressure manifold. Pressurize the indoor evaporator coil to 250 PSI and the outdoor condenser coil to 350 PSI. Monitor gauge for 30 minutes for any pressure drop.

Soap Bubble Immersion vs Electronic Halide Leak Sniffers

Apply liquid soap solution on all flare nuts, U-bends, and brazed joints. For invisible micro-leaks, immerse the pressurized coil in a workshop water testing tank.

Proper Nitrogen Purging During Brazing

When brazing copper tubing, trickle dry nitrogen at 2-3 PSI through the pipe. This prevents copper oxide flaking inside the tube, which otherwise clogs the expansion capillary or EEV strainer.

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