Refrigerant detector alarm

Troubleshooting · Applies to: Direct expansion refrigeration system · Heat pump and air conditioning · CO2 booster (transcritical) · Liquid chiller (water or brine) · Ammonia with pump circulation (R717) · Cold rooms with several evaporators

A gas detector alarm: a real leak, false alarms from other gases, a drifting sensor and a sensor in the wrong place.

Last checked: October 25, 2026 Field mode: large buttons, questions first and the screen kept on.

Treat every alarm as a real leak until proven otherwise: ventilate, do not enter a room with a high alarm without measuring, and follow the system's emergency instructions. CO2 involves a risk of asphyxiation, and A2L and A3 refrigerants a fire risk. The EU F-gas Regulation requires a leak detection system from 500 tonnes CO2e (100 kg for pure HFOs) in refrigeration, air conditioning and heat pump equipment, checked at least every 12 months (Regulation (EU) 2024/573, Article 6) ^[1]. In Switzerland a leak detection system is required from 500 tonnes CO2e and checked at least once a year; systems in operation before 1 January 2025 may lack it until 31 December 2026. From 1 January 2027 it is also required above 250 kg of HFO refrigerants, and such systems in operation before then may lack it until 31 December 2028. A leak found must be repaired at once (ChemRRV, SR 814.81, Annex 2.10 point 3.4 and transitional provisions) ^[2]. In the USA, commercial and industrial process refrigeration with a full charge of 1,500 lb (about 680 kg) or more of a refrigerant with a GWP above 53 must have an automatic leak detection system, audited and calibrated every year; systems installed 2017–2025 must have it by 1 January 2027 (40 CFR 84.108) ^[3].

Work on the refrigerant circuit may only be carried out by certified personnel. Isolate the power before working on electrical parts and take particular care with high pressures (CO2) and flammable refrigerants (A2L and A3). Always follow the manufacturer's instructions.

Confirm the fault first

Read the concentration and which sensor is alarming. Measure with a calibrated handheld instrument at the sensor and around the system, and do not enter the room at a high alarm without measuring first.

📏 Measurement guide: calculate superheat and subcooling 🔢 Alarm and fault codes

Flowchart

Causes, most likely first

The order is approximate and based on common faults in the field. Always measure before replacing anything.

1
Flowchart A
A real leak.
Remedy: Ventilate, switch off the system if needed and leak test with a calibrated instrument. Repair the leak and record the event in the logbook.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Leak test a refrigeration system
Find leaks systematically, confirm the repair and record the work. Work that opens the refrigerant circuit requires F-gas certification (Regulation (EU) 2024/573 or national equivalent, EPA 608 in the USA).
1. Prepare the system and the detector. The system must be under pressure (running, or at standstill with warm ambient). Stop fans in the area to get calm air and ventilate low or enclosed spaces. With A2L/A3 refrigerants use no ignition sources and only detectors rated for them; with CO2 (R744) remember the very high pressure. Check the electronic detector (EN 14624) against its reference leak or as the manufacturer describes.
  ✓ Check: The detector reacts to the reference leak, and the air around the system is calm.
2. Search with the electronic detector. Move the probe slowly, a few centimetres per second, close to every brazed joint, flare, valve stem, Schrader core, gauge and coil bend. Refrigerants are heavier than air, so hold the probe at and below each joint. Follow the circuit in a fixed order so that nothing is missed.
  ✓ Check: Every joint along the circuit has been passed, and each alarm has been repeated at the same spot.
3. Confirm with bubble solution. Spray bubble leak solution on each suspected point and watch it for at least a minute; small leaks form bubbles or foam slowly.
  ✓ Check: Bubbles or foam pinpoint the leak, or the point is confirmed tight.
4. Use UV dye only where it is approved. If the system already contains a UV dye approved by the compressor manufacturer, light the joints with a UV lamp and wear UV glasses.
  ✓ Check: A fluorescent trace marks the leak, or no trace is visible.
5. Repair correctly. Recover the refrigerant (or isolate the section), repair with nitrogen flowing when brazing, pressure test with nitrogen, evacuate and charge by weight. Never top up refrigerant 'to test' without finding and repairing the leak.
  ✓ Check: The repaired joint holds the nitrogen test pressure and the system is charged with the specified amount.
6. Record and re-check. Write the leak location, cause, repair, refrigerant amount and your certificate number in the equipment logbook. Check the repair again within one month, as the F-gas regulation requires.
  ✓ Check: The logbook entry is complete and a follow-up check is booked.
Test and calibrate a gas detector
A refrigerant gas detector must give its alarms at the set levels so that people are warned and ventilation starts. Test it with test gas at the interval in the manufacturer's manual and national rules, and record each test.
1. Make it safe and tell people. If the detector is in alarm now, treat it as a real leak: ventilate and leave the room before doing anything else. Before testing, tell the owner and the alarm receiver, so a test alarm does not call out the emergency service or stop the plant by surprise.
  ✓ Check: The detector shows normal and everyone affected knows a test is starting.
2. Check the sensor position. Check that the sensor is placed where the gas collects: low for refrigerants heavier than air (most HFCs, HFOs, hydrocarbons and CO2), high for ammonia. It must not be blocked or close to a door or fan that dilutes the gas.
  ✓ Check: The sensor sits at the right height and is free and clean.
3. Apply test gas. Use test gas of the refrigerant (or the gas the manual specifies) within its expiry date. Fit the calibration adaptor and apply the gas at the flow rate in the manual. For flammable refrigerants (A2L/A3) use only the manufacturer's test gas and no ignition sources.
  ✓ Check: The reading rises within the response time stated in the manual.
4. Check the alarm levels and outputs. Note the reading at which the pre-alarm and main alarm trigger and compare them with the settings for the installation. Check that every output works: siren and light, ventilation, plant shutdown and remote alarm.
  ✓ Check: Each alarm triggers at its set level and every connected output responds.
5. Calibrate if needed. If the reading is off by more than the manual allows, calibrate zero and span as the manual describes, or replace the sensor if it is past its service life.
  ✓ Check: After calibration the reading agrees with the test gas concentration.
6. Restore and record. Remove the adaptor, let the reading return to zero and reset the alarms. Record date, test gas batch, alarm levels, response, any calibration and the next due date.
  ✓ Check: The detector is back in normal mode and the record is complete.
Record work in the F-gas logbook
Leak checks, repairs and every kilogram charged or recovered must be recorded. In the EU this follows Regulation (EU) 2024/573; other countries have their own rules (USA: EPA, 40 CFR Part 82 and 84).
1. Find the right record. Open the logbook or digital register for the specific system and check that the plant ID, location and refrigerant match the nameplate.
  ✓ Check: The record belongs to the system you are working on.
2. Record who and when. Enter the date, your company's certificate number, your own F-gas certificate number and your name.
  ✓ Check: Date and both certificate numbers are entered.
3. Describe the work. Enter the type of work (leak check, repair, maintenance, installation, decommissioning), the result of any leak check, where a leak was found and how it was repaired.
  ✓ Check: Someone else can understand from the entry what was done and found.
4. Record the quantities. Enter the refrigerant type and the quantity added and recovered in kg, read from the scale. For recovered refrigerant, note whether it is to be recycled, reclaimed or destroyed and where it goes. The CO2 equivalent can be added.
  ✓ Check: Quantities in kg match the scale readings.
5. Plan the follow-up. After a leak repair, the system must be checked again by certified personnel within one month. Note that date and the next periodic leak check.
  ✓ Check: Both dates are written in the logbook.
6. Sign and keep. Sign the entry and give the operator a copy if the logbook is not kept on site. The operator keeps the records for at least five years.
  ✓ Check: The entry is signed and the operator has access to it.
Leak check of refrigeration systems: F-gas intervals and steps →
2
Flowchart D
The leak comes from somewhere else, or the sensor is in the wrong place.
Remedy: Leak test the whole system and adjacent rooms. Check the sensor location: heavy refrigerants like CO2 and most HFCs collect near the floor.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Leak test a refrigeration system
Find leaks systematically, confirm the repair and record the work. Work that opens the refrigerant circuit requires F-gas certification (Regulation (EU) 2024/573 or national equivalent, EPA 608 in the USA).
1. Prepare the system and the detector. The system must be under pressure (running, or at standstill with warm ambient). Stop fans in the area to get calm air and ventilate low or enclosed spaces. With A2L/A3 refrigerants use no ignition sources and only detectors rated for them; with CO2 (R744) remember the very high pressure. Check the electronic detector (EN 14624) against its reference leak or as the manufacturer describes.
  ✓ Check: The detector reacts to the reference leak, and the air around the system is calm.
2. Search with the electronic detector. Move the probe slowly, a few centimetres per second, close to every brazed joint, flare, valve stem, Schrader core, gauge and coil bend. Refrigerants are heavier than air, so hold the probe at and below each joint. Follow the circuit in a fixed order so that nothing is missed.
  ✓ Check: Every joint along the circuit has been passed, and each alarm has been repeated at the same spot.
3. Confirm with bubble solution. Spray bubble leak solution on each suspected point and watch it for at least a minute; small leaks form bubbles or foam slowly.
  ✓ Check: Bubbles or foam pinpoint the leak, or the point is confirmed tight.
4. Use UV dye only where it is approved. If the system already contains a UV dye approved by the compressor manufacturer, light the joints with a UV lamp and wear UV glasses.
  ✓ Check: A fluorescent trace marks the leak, or no trace is visible.
5. Repair correctly. Recover the refrigerant (or isolate the section), repair with nitrogen flowing when brazing, pressure test with nitrogen, evacuate and charge by weight. Never top up refrigerant 'to test' without finding and repairing the leak.
  ✓ Check: The repaired joint holds the nitrogen test pressure and the system is charged with the specified amount.
6. Record and re-check. Write the leak location, cause, repair, refrigerant amount and your certificate number in the equipment logbook. Check the repair again within one month, as the F-gas regulation requires.
  ✓ Check: The logbook entry is complete and a follow-up check is booked.
Test and calibrate a gas detector
A refrigerant gas detector must give its alarms at the set levels so that people are warned and ventilation starts. Test it with test gas at the interval in the manufacturer's manual and national rules, and record each test.
1. Make it safe and tell people. If the detector is in alarm now, treat it as a real leak: ventilate and leave the room before doing anything else. Before testing, tell the owner and the alarm receiver, so a test alarm does not call out the emergency service or stop the plant by surprise.
  ✓ Check: The detector shows normal and everyone affected knows a test is starting.
2. Check the sensor position. Check that the sensor is placed where the gas collects: low for refrigerants heavier than air (most HFCs, HFOs, hydrocarbons and CO2), high for ammonia. It must not be blocked or close to a door or fan that dilutes the gas.
  ✓ Check: The sensor sits at the right height and is free and clean.
3. Apply test gas. Use test gas of the refrigerant (or the gas the manual specifies) within its expiry date. Fit the calibration adaptor and apply the gas at the flow rate in the manual. For flammable refrigerants (A2L/A3) use only the manufacturer's test gas and no ignition sources.
  ✓ Check: The reading rises within the response time stated in the manual.
4. Check the alarm levels and outputs. Note the reading at which the pre-alarm and main alarm trigger and compare them with the settings for the installation. Check that every output works: siren and light, ventilation, plant shutdown and remote alarm.
  ✓ Check: Each alarm triggers at its set level and every connected output responds.
5. Calibrate if needed. If the reading is off by more than the manual allows, calibrate zero and span as the manual describes, or replace the sensor if it is past its service life.
  ✓ Check: After calibration the reading agrees with the test gas concentration.
6. Restore and record. Remove the adaptor, let the reading return to zero and reset the alarms. Record date, test gas batch, alarm levels, response, any calibration and the next due date.
  ✓ Check: The detector is back in normal mode and the record is complete.
3
Flowchart B
False alarm: the sensor reacts to other gases (cross-sensitivity), or to humidity and condensation (common for semiconductor sensors in cold rooms, after defrost or washing).
Remedy: Remove the source and test the sensor with test gas. Protect the sensor from water and condensation, and switch to a sensor type less sensitive to the interference if the alarms recur.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Test and calibrate a gas detector
A refrigerant gas detector must give its alarms at the set levels so that people are warned and ventilation starts. Test it with test gas at the interval in the manufacturer's manual and national rules, and record each test.
1. Make it safe and tell people. If the detector is in alarm now, treat it as a real leak: ventilate and leave the room before doing anything else. Before testing, tell the owner and the alarm receiver, so a test alarm does not call out the emergency service or stop the plant by surprise.
  ✓ Check: The detector shows normal and everyone affected knows a test is starting.
2. Check the sensor position. Check that the sensor is placed where the gas collects: low for refrigerants heavier than air (most HFCs, HFOs, hydrocarbons and CO2), high for ammonia. It must not be blocked or close to a door or fan that dilutes the gas.
  ✓ Check: The sensor sits at the right height and is free and clean.
3. Apply test gas. Use test gas of the refrigerant (or the gas the manual specifies) within its expiry date. Fit the calibration adaptor and apply the gas at the flow rate in the manual. For flammable refrigerants (A2L/A3) use only the manufacturer's test gas and no ignition sources.
  ✓ Check: The reading rises within the response time stated in the manual.
4. Check the alarm levels and outputs. Note the reading at which the pre-alarm and main alarm trigger and compare them with the settings for the installation. Check that every output works: siren and light, ventilation, plant shutdown and remote alarm.
  ✓ Check: Each alarm triggers at its set level and every connected output responds.
5. Calibrate if needed. If the reading is off by more than the manual allows, calibrate zero and span as the manual describes, or replace the sensor if it is past its service life.
  ✓ Check: After calibration the reading agrees with the test gas concentration.
6. Restore and record. Remove the adaptor, let the reading return to zero and reset the alarms. Record date, test gas batch, alarm levels, response, any calibration and the next due date.
  ✓ Check: The detector is back in normal mode and the record is complete.
4
Flowchart C
The sensor has drifted or is worn out.
Remedy: Calibrate or replace the sensor and record the check in the logbook.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Test and calibrate a gas detector
A refrigerant gas detector must give its alarms at the set levels so that people are warned and ventilation starts. Test it with test gas at the interval in the manufacturer's manual and national rules, and record each test.
1. Make it safe and tell people. If the detector is in alarm now, treat it as a real leak: ventilate and leave the room before doing anything else. Before testing, tell the owner and the alarm receiver, so a test alarm does not call out the emergency service or stop the plant by surprise.
  ✓ Check: The detector shows normal and everyone affected knows a test is starting.
2. Check the sensor position. Check that the sensor is placed where the gas collects: low for refrigerants heavier than air (most HFCs, HFOs, hydrocarbons and CO2), high for ammonia. It must not be blocked or close to a door or fan that dilutes the gas.
  ✓ Check: The sensor sits at the right height and is free and clean.
3. Apply test gas. Use test gas of the refrigerant (or the gas the manual specifies) within its expiry date. Fit the calibration adaptor and apply the gas at the flow rate in the manual. For flammable refrigerants (A2L/A3) use only the manufacturer's test gas and no ignition sources.
  ✓ Check: The reading rises within the response time stated in the manual.
4. Check the alarm levels and outputs. Note the reading at which the pre-alarm and main alarm trigger and compare them with the settings for the installation. Check that every output works: siren and light, ventilation, plant shutdown and remote alarm.
  ✓ Check: Each alarm triggers at its set level and every connected output responds.
5. Calibrate if needed. If the reading is off by more than the manual allows, calibrate zero and span as the manual describes, or replace the sensor if it is past its service life.
  ✓ Check: After calibration the reading agrees with the test gas concentration.
6. Restore and record. Remove the adaptor, let the reading return to zero and reset the alarms. Record date, test gas batch, alarm levels, response, any calibration and the next due date.
  ✓ Check: The detector is back in normal mode and the record is complete.
Record work in the F-gas logbook
Leak checks, repairs and every kilogram charged or recovered must be recorded. In the EU this follows Regulation (EU) 2024/573; other countries have their own rules (USA: EPA, 40 CFR Part 82 and 84).
1. Find the right record. Open the logbook or digital register for the specific system and check that the plant ID, location and refrigerant match the nameplate.
  ✓ Check: The record belongs to the system you are working on.
2. Record who and when. Enter the date, your company's certificate number, your own F-gas certificate number and your name.
  ✓ Check: Date and both certificate numbers are entered.
3. Describe the work. Enter the type of work (leak check, repair, maintenance, installation, decommissioning), the result of any leak check, where a leak was found and how it was repaired.
  ✓ Check: Someone else can understand from the entry what was done and found.
4. Record the quantities. Enter the refrigerant type and the quantity added and recovered in kg, read from the scale. For recovered refrigerant, note whether it is to be recycled, reclaimed or destroyed and where it goes. The CO2 equivalent can be added.
  ✓ Check: Quantities in kg match the scale readings.
5. Plan the follow-up. After a leak repair, the system must be checked again by certified personnel within one month. Note that date and the next periodic leak check.
  ✓ Check: Both dates are written in the logbook.
6. Sign and keep. Sign the entry and give the operator a copy if the logbook is not kept on site. The operator keeps the records for at least five years.
  ✓ Check: The entry is signed and the operator has access to it.
5
A fault in the detector supply or cable gives a false signal that alarms.
Remedy: Check the supply, cable and the detector fault codes.
🛠 How do I do it? Step by step
Only qualified personnel may work on refrigeration and electrical systems. Follow the manufacturer's manual and local rules; the steps are guidance, not a replacement for training.
Test and calibrate a gas detector
A refrigerant gas detector must give its alarms at the set levels so that people are warned and ventilation starts. Test it with test gas at the interval in the manufacturer's manual and national rules, and record each test.
1. Make it safe and tell people. If the detector is in alarm now, treat it as a real leak: ventilate and leave the room before doing anything else. Before testing, tell the owner and the alarm receiver, so a test alarm does not call out the emergency service or stop the plant by surprise.
  ✓ Check: The detector shows normal and everyone affected knows a test is starting.
2. Check the sensor position. Check that the sensor is placed where the gas collects: low for refrigerants heavier than air (most HFCs, HFOs, hydrocarbons and CO2), high for ammonia. It must not be blocked or close to a door or fan that dilutes the gas.
  ✓ Check: The sensor sits at the right height and is free and clean.
3. Apply test gas. Use test gas of the refrigerant (or the gas the manual specifies) within its expiry date. Fit the calibration adaptor and apply the gas at the flow rate in the manual. For flammable refrigerants (A2L/A3) use only the manufacturer's test gas and no ignition sources.
  ✓ Check: The reading rises within the response time stated in the manual.
4. Check the alarm levels and outputs. Note the reading at which the pre-alarm and main alarm trigger and compare them with the settings for the installation. Check that every output works: siren and light, ventilation, plant shutdown and remote alarm.
  ✓ Check: Each alarm triggers at its set level and every connected output responds.
5. Calibrate if needed. If the reading is off by more than the manual allows, calibrate zero and span as the manual describes, or replace the sensor if it is past its service life.
  ✓ Check: After calibration the reading agrees with the test gas concentration.
6. Restore and record. Remove the adaptor, let the reading return to zero and reset the alarms. Record date, test gas batch, alarm levels, response, any calibration and the next due date.
  ✓ Check: The detector is back in normal mode and the record is complete.

Checks from the manufacturers’ manuals (14)

Values and checks the manufacturers give for their own products; they apply to the product named.

Danfoss DGS: minimum calibration intervals are 60 months for infrared (IR), 12 months for semiconductor (SC) and 6 months for electrochemical (PE), with a yearly bump test for IR in between.^[4]
Danfoss DGS: HFCs, CO2 and propane are heavier than air, so mount the sensor head about 30 cm above the floor, preferably in the air flow; a detector mounted high may stay silent during a leak.^[4]
Heatcraft A2L unit coolers: the leak controller needs its own uninterrupted 24 V supply; after an alarm, repair the leak and hold Reset/Test over 3 s (just over 1 s starts a 2-minute test).^[5]
Hussmann pumped CO2: the CO2 leak detector alarm is adjustable within 4000–9000 ppm; check the actual setpoint before judging a reading as a leak.^[6]
Danfoss DGS with semiconductor sensor (SC): the zero point drifts with temperature, moisture, cleaning agents and exhaust from trucks, so readings below about 75 ppm are ignored and not zero-adjusted; for alarms without a leak, set an alarm delay and do a bump test. A green flashing LED means the calibration interval is exceeded or the sensor is worn out.^[7]
Danfoss GD detectors: the calibration gas must be 30–90 % of the measuring range; if the sensitivity has fallen below 30 % the head cannot be calibrated and must be replaced. An over-temperature error often comes from direct sunlight on the detector.^[8]
Danfoss Gas Detection controller unit and expansion module: Gas detector with 4–20 mA sensors: a signal above about 21 mA means a short circuit or an uncalibrated or faulty sensor, below about 3 mA a broken wire. A head in direct sun or a hot place can go to an overtemperature fault, and calibration with the wrong test gas gives over-range readings.^[9]
Krack MK-A2L/MV-A2L unit coolers: A factory-fitted A2L leak sensor tests itself and also starts the leak mitigation (fans on, refrigeration stopped) when it has an internal fault or reaches end of life (about 15 years), so the alarm looks like a leak; the sensor must then be replaced. A blocked membrane, or cleaning sprays and solvents on the sensor, also disturb it.^[10]
Copeland/Dixell RLDS refrigerant leak detection system: Aspirated multi-zone infrared monitors re-zero from a purge line that must draw clean air. If the purge inlet is in a plant room or other contaminated air the baseline shifts and readings go wrong; for CO2 the purge line must run outdoors away from CO2 sources, and a charcoal purge filter must not be used with NH3 or CO2.^[11]
Copeland/Dixell RLDS: Sample points: halocarbon refrigerants about 15–45 cm above the floor, CO2 in the breathing zone about 1.2–1.8 m (this maker differs from those who place CO2 near the floor). Sample tubes must have no kinks and bends no tighter than about 127 mm radius.^[11]
Danfoss DGS; Krack KR-A2L built-in A2L sensor: Semiconductor and catalytic sensors can be poisoned by silicone vapour from fresh sealant, and disturbed by cleaning sprays. Keep the protective cap on until the silicone has cured, and do not spray cleaners on the sensor or cover its membrane.^[12]
Danfoss DGS: Check when the sensor was last calibrated: Danfoss recommends at most 60 months for infrared, 12 months for semiconductor and 6 months for catalytic (pellistor) sensors, and a bump test or new sensor after a large propane leak. A flashing green LED means calibration due or end of life.^[13]
Danfoss DGS: Mounting height follows the gas density: for gases heavier than air (HFC, CO2, propane) about 0.3-0.5 m above the floor, in the air flow but not right at an air outlet or suction opening; use a wind shield above about 6 m/s air speed.^[13]
Krack KR-A2L unit coolers: Built-in A2L sensors in unit coolers: test at least once a year with gas from an unlit lighter held at the sensor; the alarm must come within 60 seconds, the liquid solenoid must close and the fans start. The alarm only resets when the reading has fallen about 2.5 % below the threshold.^[14]

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Terms in this article

Leakage detection system Leak check Practical limit

Refrigerant detector alarm

Confirm the fault first

Troubleshoot step by step

Flowchart

Causes, most likely first

Leak test a refrigeration system

Test and calibrate a gas detector

Record work in the F-gas logbook

Leak test a refrigeration system

Test and calibrate a gas detector

Test and calibrate a gas detector

Test and calibrate a gas detector

Record work in the F-gas logbook

Test and calibrate a gas detector

Checks from the manufacturers’ manuals (14)

Service report

Calculate it yourself

Terms in this article

Sources

Confirm the fault first

Troubleshoot step by step

Flowchart

Causes, most likely first

Leak test a refrigeration system

Test and calibrate a gas detector

Record work in the F-gas logbook

Leak test a refrigeration system

Test and calibrate a gas detector

Test and calibrate a gas detector

Test and calibrate a gas detector

Record work in the F-gas logbook

Test and calibrate a gas detector

Checks from the manufacturers’ manuals (14)

Service report

Calculate it yourself

Terms in this article

Sources

Read also