Nitrogen Pressure / Leak Test

Pressurize the refrigerant circuit with DRY NITROGEN through a regulator (never oxygen, never refrigerant) to the listed test pressure, hold and watch for pressure decay accounting for temperature, locate leaks by bubble/electronic detection, then relieve safely.

Approx. 90 min

Before you start

•All joints brazed/pressed and the system fully assembled — this test comes BEFORE evacuation; never pull a vacuum to find leaks.
•Equipment's maximum test pressures known (high-side vs low-side design pressures and any service-valve / component limits), and a fresh dry-nitrogen cylinder with a working regulator on hand.
•Refrigerant type identified so the listed/working pressures and detector are correct.

Tools & materials

Dry-nitrogen cylinder + pressure regulator (with a high-enough range) · Manifold/gauge able to read the test pressure · Bubble leak-detection solution · Electronic leak detector · Temperature reference (to interpret pressure changes)

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Use dry nitrogen — never oxygen or refrigerant

Pressurize with dry nitrogen through a regulator
Use dry nitrogen ONLY, fed through a pressure regulator. Never use oxygen — oxygen plus compressor/refrigerant oil under pressure can detonate. Never use refrigerant to pressure-test: it's illegal to vent, expensive, and a poor leak medium. Always regulate; an unregulated cylinder can reach thousands of psi.
Target: Dry nitrogen via a regulator; cylinder pressure regulated down before it reaches the system
⚠ NEVER use oxygen (explosion hazard with oil) and never use refrigerant to pressure-test. Always use a regulator — straight cylinder pressure can rupture components and is a serious injury hazard.

Pressurize to the listed pressure

Bring the system to the listed test pressure
Slowly regulate nitrogen into the circuit up to the manufacturer/listed test pressure. Respect the lowest-rated component in the loop — the low side and high side have different design pressures, so don't exceed the low-side rating if both are connected. Stay within DOT/equipment limits.
Target: Test to the maker's listed pressure (e.g. low side often ~150 psig, high side higher per nameplate); never exceed the lowest component rating or the equipment limit
⚠ Do not over-pressurize past the lowest-rated component or service-valve limit — components can burst.

Hold & watch for decay

Isolate, hold, and watch for pressure decay
Valve off the nitrogen source and let the system sit, ideally an hour or more (overnight for big/critical jobs). A holding pressure means tight; a falling pressure means a leak. Account for temperature: gas pressure rises/falls with temperature, so a pressure change that tracks a temp swing (sun on the lines, day-to-night) is not necessarily a leak — note ambient temp at start and end.
Target: Pressure holds over the test window; correct any apparent change for temperature (a real leak loses pressure independent of temp)

Locate leaks

Find leaks by bubble and electronic detection
If pressure drops, brush bubble solution on every joint and watch for growing bubbles, and/or sweep an electronic detector along the joints and components. Mark, relieve pressure, repair, then re-test — don't chase one leak and assume it's the only one.
Tools: Bubble leak solution, Electronic leak detector
Target: Every joint checked; all leaks found and repaired, then the hold test re-run clean

Relieve safely

Relieve the nitrogen safely
Once the system holds, bleed the nitrogen off in a controlled way to a safe area. Nitrogen is inert but displaces oxygen — vent in a ventilated space, not a sealed room. Then proceed to evacuation.
Target: Nitrogen bled down controlled in a ventilated area before evacuation
⚠ Nitrogen displaces oxygen — never vent large volumes in a confined/unventilated space (asphyxiation risk).