Electronic Leak Detector: What the Alarm Does Not Prove

A leak detector answers one question: how much refrigerant is in the air drawn through its probe at this moment. A pump pulls a sample past a sensor, and the sensor reports what it finds. Everything said afterwards is interpretation laid on top.

Air concentration and leak position are different quantities. INFICON explains that gap in its manual. Refrigerant leaving a system does not spread evenly and is denser than air, so it gathers into clouds that sit low, colourless and odourless. A common detector alarms on walking into one, but the manual says that does not help find the leak, since the cloud may not sit near its source.

The instrument also has to be told what counts as nothing. Testo's manual for the 316-4 describes zeroing as standardising to the current gas concentration: whatever refrigerant hangs in the air at that moment becomes the new zero. A detector zeroed in escaped gas has quietly agreed to ignore it.

One tool can be set to answer either of two questions, which Testo names as modes. Localisation mode optimises sensitivity to the change in the signal, search mode to the leakage quantity. One setting chases a gradient, the other weighs how much is present.

So a beep carries less information than its confidence suggests. It establishes that vapour the sensor responds to reached the tip during the sweep. It does not establish where that vapour started, how much is escaping, or whether the source is the joint the probe passed.

Sensitivity is a specification with conditions attached, and the conditions matter more than the number. Bacharach's datasheet for the H-10 PRO prints two figures for one instrument: 0.006 oz/yr stationary, and 0.1 oz/yr moving, measured per SAE J2791.

That is a gap of roughly seventeen times, on the same page for one tool. The larger figure applies while a probe is swept along a pipe, which is how the instrument gets used. A footnote adds conditions: a named list of refrigerants, the small leak setting, manual mode.

Background gas moves the number. INFICON's specification table gives a minimum sensitivity of 1 g/yr for R134a in clean conditions; in a contaminated environment the same row reads greater than 2 g/yr. Refrigerant in the air costs the instrument at least half its rating, and a leak hunt happens exactly there.

Which gas is escaping matters too. Testo rates the 316-4 at under 3 g/a, qualified as specified for reference refrigerants. Its table lists R410A as detectable, while the reference gas behind the threshold is R134a. The figure was never established on R410A.

None of this makes the numbers dishonest; it makes a bare number useless. A figure with no probe condition, refrigerant or setting behind it describes a laboratory, and the joint is on a ledge.

Cross sensitivity is designed for, not incidental. EN 14624 lists cross sensitivity from interference gases among its minimum requirements. A problem written into a standard's scope is old and well understood.

INFICON's D-TEK Stratus manual prints the evidence. A table of workshop chemicals marks which ones cause a false trigger. Methanol-based windscreen washer solvent triggers it; so do a spot and stain remover, a rust penetrant, gasket and trim adhesive, cleaner and degreaser, brake parts cleaner, carburettor cleaner and clear silicone rubber.

Several other liquids do not. The same table marks antifreeze, brake fluid, silicone lubricant, transmission fluid, mineral engine oil and pumice hand cleaner as safe. Volatile solvents, aerosol degreasers and curing adhesives set it off; heavier oils and water-based fluids do not.

That list carries weight because the D-TEK Stratus is an infrared instrument. Infrared is the selective sensing technology, and it still responds to cleaning products; Bacharach's H-10 PRO uses a heated diode, described as ultra-sensitive to halogen-based refrigerants, so it casts a wider net. Testo's 316-4 uses a gas-sensitive semiconductor. Three technologies, three response profiles, one shared weakness.

Nothing about a leak hunt keeps those substances away. A coil that has been chemically cleaned, a joint wiped with solvent, a bracket sealed with silicone, a cabinet sprayed with degreaser: each leaves lingering residue. An alarm over that joint is a true reading about the air and a false one about the system.

Two further triggers have nothing to do with chemistry. INFICON warns that high radio-frequency environments may cause a false alarm, and that blocking the exhaust port can cause false alarms or readings. An instrument can be wrong over where it stands and how it is held.

A detector fails quietly. It does not stop working in a way anyone notices; it grows less sensitive, and a less sensitive instrument produces clean sweeps. Testo's troubleshooting page names the symptom plainly: an instrument that seems to ignore leaks, or misses some refrigerants, has a spent sensor.

Service life is short, counted in running hours. Testo puts the 316-3 sensor at 80 to 100 hours, about a year of normal use. Bacharach gives the H-10 PRO sensor a typical life of one year, and adds that consistent exposure to high refrigerant levels deteriorates it faster.

Makers treat the sensing element as a consumable. INFICON's warranty excludes items that deteriorate under normal use: batteries, sensors, filters. The instrument carries a warranty; the part doing the detecting does not.

Dirt does the same damage faster. Testo warns that tobacco smoke, dirty air, oils, grease and evaporating liquids leave deposits on the sensor, reducing sensitivity and falsifying the display; oils can destroy it outright. Refrigerant leaving a system carries oil out with it.

Warm-up is the other gap. INFICON's D-TEK Stratus finishes warm-up in 45 to 90 seconds, and the manual recommends running it for 15 minutes to reach the specified sensitivities. A detector switched on at the door and used a minute later sits inside its working range and outside its rated one.

Makers answer all of this one way: check against a known leak. INFICON gives a calibration frequency of an annual check with a calibrated leak standard, Testo recommends yearly servicing at an authorised centre, and the handling code asks for periodic calibration. A beep reveals none of it, so the tool's age is fair to ask about.

The codified answer is to use two methods. The Australian and New Zealand handling code calls it best practice to combine techniques: an electronic detector to test an area, then leak detection spray to identify and verify the exact location. The detector narrows; something else confirms.

That same code limits what a silent detector settles. Where a leak is suspected but not found, it requires refrigerant removal and a tightness test on the section. A sweep that found nothing is not a finding of no leak.

Open air is where the instrument is weakest. The code notes that a hand-held detector may not function well on plant located outdoors, and that indirect detection covers equipment in well-ventilated environments. It also requires the procedure to account for the distance between leak and testing equipment. In Singapore the condenser usually lives on an open ledge.

Makers ask for a retest even when the alarm looked convincing. INFICON advises rechecking an apparent leak found at the most sensitive setting, particularly where the probe was held static against a joint, and repeating it with the probe moving. A probe pressed onto one spot easily produces a hit that fails a second look.

The useful question is never whether the detector alarmed. It is what happened next. A joint named from a beep alone, with no second method and no repeat, is a suspect promoted to a conclusion with the middle step missing.

That middle step separates a repair from a refill. Refrigerant put into a circuit whose leak was never confirmed buys time and nothing else. Shrinking the search is the instrument's real job, and it pays only once something else has found the spot.