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What Is a Refrigerant Leak Detector?

Refrigerant leak detectors trace where an air conditioner or fridge is losing charge. Heated diode and infrared sensors dominate, with different sensitivities and lifespans, and the newer flammable refrigerants change which sensor is appropriate.

By the Akermin Editorial Team · 3 min read

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A refrigerant leak detector is a handheld sniffer with a probe that senses refrigerant gas in air at very low concentrations and indicates it with a tick rate, bar graph or number, so a technician can trace a leak to a joint, valve or coil. Heated-diode sensors are sensitive and inexpensive; infrared sensors are more selective and longer-lived and are becoming the standard for the flammable A2L refrigerants now in new equipment. Sensitivity is stated in grams per year of leak rate, and the good ones detect 3 g/yr or better.

Sensor types

Sensor How it works Detects Notes
Heated diode Refrigerant molecules break down on a heated element, releasing halogen ions that change a current CFC, HCFC, HFC; some HFO Sensitive; sensor life about 1 to 2 years; false alarms on some oils and solvents; needs warm-up
Infrared Refrigerant absorbs infrared at specific wavelengths in a sample cell HFC, HFO, A2L blends, CO₂ (with appropriate optics) Selective; long sensor life (5 to 10 years); stable; higher cost; the Inficon D-TEK 3 and Fieldpiece infrared units are examples
Corona discharge Halogens change the current across a high-voltage spark Halogenated refrigerants Older technology; prone to false alarms
Ultrasonic Hears the hiss of gas escaping under pressure Any gas, any refrigerant Finds large leaks fast in noisy environments; poor for small leaks
Semiconductor (MOS) Resistance change of a heated oxide film Hydrocarbon refrigerants (R-290, R-600a) and many others Non-specific; used in combined combustible/refrigerant sniffers

Sensitivity and standards

Leak rate sensitivity is quoted in grams of refrigerant per year: 3 g/yr is the common professional benchmark, and premium infrared detectors reach under 1 g/yr. Standards define test methods: EN 14624 in Europe, SAE J2791 (HFC) and J2913 (HFO) in the US automotive sector. Regulations for larger commercial systems require periodic leak checks with instruments meeting these. See why gas sensor response time matters for the speed side.

Refrigerant classes

  • HFC (R-134a, R-410A, R-404A): non-flammable; detected by all halogen-sensitive types.
  • HFO (R-1234yf, R-1234ze): mildly flammable (A2L); detected by infrared and newer heated-diode units.
  • A2L blends (R-32, R-454B, R-452B): mildly flammable; require detectors rated for them, and often intrinsically safe designs.
  • Hydrocarbons (R-290 propane, R-600a isobutane): flammable; detected by semiconductor combustible sensors, not by halogen detectors.
  • CO₂ (R-744): needs an infrared CO₂ sensor; a halogen detector cannot see it.
  • Ammonia (R-717): needs an ammonia-specific electrochemical sensor.

Searching for a leak

  1. Warm up in clean air; let the detector zero. See how to test a refrigerant leak detector before use.
  2. Turn off fans and close doors; moving air disperses the gas.
  3. Move the probe slowly (a few centimeters per second) along every joint, flare, Schrader valve, service port, brazed connection and coil return bend, keeping the tip within about 5 mm of the surface.
  4. Refrigerants are heavier than air; check below joints and at the lowest points of the system.
  5. When the detector indicates, back off, let it recover, and approach again to pinpoint.
  6. Confirm with leak-detection bubbles before repair.

Maintenance

Heated-diode sensors wear out and must be replaced on schedule; infrared sensors last years. Keep the probe filter clean; oil on the tip ruins sensitivity. Verify against a reference leak before each job. Detectors are covered in the gas detection category; the infrared versus heated-diode choice is detailed in infrared vs heated-diode refrigerant leak detectors.

Fieldpiece - DR58 Heated Diode Refrigerant Leak Detector - Ultra-Sensitive Leak Sniffer with Large, Backlite LCD Screen - Lightweight HVAC Tool

Fieldpiece - DR58 Heated Diode Refrigerant Leak Detector - Ultra-Sensitive

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Inficon D-TEK 3 Refrigerant Leak Detector

Inficon D-TEK 3 Refrigerant Leak Detector

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Elitech HVAC Refrigerant Leak Detector Heated Diode Sensor Halogen Freon Sniffer, Air Conditioning Detection, R22 R410A R134A R1234YF CFCs HCFCs HFCs, ILD-100H

Elitech HVAC Refrigerant Leak Detector Heated Diode Sensor Halogen Freon

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

What sensitivity should a refrigerant leak detector have?

Good detectors state 3 g/yr or better for HFCs; premium infrared units reach 1 g/yr or below. Regulations for larger systems require detectors meeting EN 14624 or SAE J2791 / J2913.

Can it detect the new A2L refrigerants like R-32 and R-454B?

Only if rated for them. Infrared detectors tuned for HFC/HFO generally can; many older heated-diode units cannot. Check the specification.

Why does it alarm near oil or cleaner?

Heated-diode sensors respond to some hydrocarbons and solvents. Infrared sensors are more selective. Let the detector settle in clean air and confirm suspect leaks with bubbles.

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