INTRO (0:00 to 0:30)
Voiceover, cold open on a gauge set reading low: D24 taught you to prove a low charge instead of assuming one. Here is the part nobody can skip: refrigerant does not wear out and it does not evaporate into nothing. A system that is truly low has a hole, and a leak search before recharge is required, not optional. Today you learn the three jobs of leak hunting, the four tools that do them, why eighty percent of your leaks live in one component, and the one test that ends every argument.
ON-SCREEN: D27 Leak Detection Mastery
ON-SCREEN: Confirmed low charge = there is a hole. Find it before you fill it
MAIN (0:30 to 4:15)
[0:30-1:20] Locate, confirm, prove: the fixed order
Voiceover over D27-detection-methods-matrix.svg: Every leak tool does exactly one of three jobs. The electronic detector LOCATES: it narrows a whole system down to a joint or a few inches of tube. Heated diode or infrared, both in the 0.1 ounce per year sensitivity class; the diode is a consumable sensor that false-alarms on household chemicals, the infrared lives longer and shrugs off big hits. Bubbles CONFIRM: a detector hit is a suspicion until solution foams on the exact spot you can photograph. Nitrogen PROVES: only a standing pressure test can demonstrate a system is tight. UV dye is the specialist, for ghost leaks that need time-lapse evidence, and it is the wrong first move almost every time: it needs runtime, it needs days, and it contaminates the oil. The order never changes: locate with the detector while the charge is still in there feeding it trace gas, confirm with bubbles, then prove with nitrogen.
ON-SCREEN: D27-detection-methods-matrix.svg, highlight each row as named
ON-SCREEN: LOCATE = detector. CONFIRM = bubbles. PROVE = nitrogen. Dye = ghosts only
[1:20-2:05] The sweep, and the two liars
Voiceover over detector B-roll: Technique decides whether the detector finds anything. Refrigerant is heavier than air, so the plume falls: probe the UNDERSIDE of every joint, and on vertical surfaces start high and work down. Move 1 to 2 inches per second with the tip within a quarter inch, because the sensor needs dwell time in the plume. And know the two conditions that fool every detector made. Wind dilutes and relocates the plume, so a breeze hands you a confident hit two feet from the real hole: block it or hunt in the calm morning. Pooling is the opposite: in a closet or a cabinet bottom, weeks of seepage builds a fog and everything alarms at once. Ventilate, let the pool drain, re-sweep, and trust the spot that lights up first.
ON-SCREEN: 1 to 2 in/sec, tip within 1/4 inch, underside of every joint
ON-SCREEN: Wind moves the plume. Pooling alarms everywhere. Manage the air first
[2:05-2:55] Where leaks live: the 80 percent map
Voiceover over D27-acoil-leak-zones.svg: The hunt has a map. Field data built on the NIST fault studies puts 80 percent of refrigerant leaks in the A-coil, the indoor evaporator. The detector goes there first, every hunt: hairpin U-bends, the distributor capillaries, the suction header brazes, and the wet lower third of the slab. The other twenty percent: Schrader cores in the service ports, field braze joints, rub-outs where vibrating copper touched anything for ten thousand hours, and flare connections, which is your mini-split note, because every mini-split tie-in lives on flares. Now over D27-formicary-corrosion.svg: the engine behind the 80 percent is formicary corrosion, ant-nest tunnels eaten through the copper by formic and acetic acid. The acid comes from the house itself: formaldehyde off-gassing from cabinets and carpet glue, cleaners, paints, all dissolving into the condensate film on a coil that is wet eight months a year. The tunnels are invisible from outside, they perforate young coils at 2 to 10 years old, and they never come alone. A formicary pinhole is a whole-coil condition, not a repair spot.
ON-SCREEN: D27-acoil-leak-zones.svg, 80 percent banner highlighted
ON-SCREEN: D27-formicary-corrosion.svg
ON-SCREEN: Copper + moisture + oxygen + household acids = tunnels. Young coils, multiple holes
[2:55-3:50] The gold standard, with the arithmetic
Voiceover over D27-nitrogen-standing-pressure.svg, following the timeline left to right: The standing pressure test is the only proof in the toolbox. Recover the charge, connect dry nitrogen through a regulator, never oxygen or compressed air, which can detonate against refrigerant oil. Pressurize to 150 to 200 psig, never above the nameplate test rating. Record pressure AND temperature. Wait: thirty minutes minimum for a repair, overnight for a slow weeper. Then correct for temperature before any verdict, because nitrogen pressure tracks absolute temperature. The trap, on screen: 150 psig at 95 F in the evening reads 144 at 75 F in the morning. Six psi lost? Run it: 164.7 absolute, times 535 over 555, is 144.1 psig. The expected reading IS 144. That system is tight; the night took the six psi, not a hole. Rule of thumb at 150 psig: about 1 psi per 3 degrees. Anything beyond that is a leak talking.
ON-SCREEN: D27-nitrogen-standing-pressure.svg, formula and worked example highlighted
ON-SCREEN: 150 at 95 F to 144 at 75 F = TIGHT. Correct before you call it
[3:50-4:15] The decision and the rule
Voiceover over D27-repair-vs-replace-flow.svg: A found leak forces a decision. Cores, flares, accessible brazes, rub-outs: repair them, prove them with nitrogen, then C15 and C16 take it from there. A leak in the coil body itself, especially with formicary signatures, makes the coil the repair unit, and on an aging R-410A system that question now runs into the A2L transition: no new R-410A equipment since the start of 2025. The decision factors are module A31 territory. And the federal frame: leak rate thresholds of 30, 20, and 10 percent apply at 50 pounds of charge and up, mostly commercial. The old 35 and 15 are pre-2019 history. Below 50 pounds the rule is simpler and it is ours: no recharge without a search.
ON-SCREEN: D27-repair-vs-replace-flow.svg
ON-SCREEN: 30/20/10 at 50 lb+. Legacy 35/15 = pre-2019, flag it. Residential = search every time
OUTRO (4:15 to 4:30)
Voiceover: In the demo video, Darrel hunts a real leak on camera: electronic sweep, bubble confirmation, and a standing pressure test with the temperature math done in the open. Watch how slow his probe hand moves. That speed is the skill.
ON-SCREEN: Next: D27 field demo, a real hunt from sweep to proven verdict