A2L Refrigerant Leak Detection
Some modern air-conditioning and heat-pump systems use A2L refrigerants. These refrigerants have lower flammability than more highly flammable refrigerants, but their flammability characteristics require technicians to recognize equipment safety features that may include refrigerant leak detection.
A refrigerant leak detector or sensor may be installed near the indoor evaporator or elsewhere within the equipment where leaking refrigerant can be detected.
This lesson focuses on recognizing these sensors and understanding why they are present. The detailed operation of leak-mitigation controls and control boards is outside the scope of this lesson.
What You Will Learn
By the end of this lesson you should be able to:
Understand that A2L refrigerants have different flammability characteristics from the traditional A1 refrigerants commonly encountered in older comfort-cooling equipment.
Describe why some equipment using A2L refrigerants includes sensors that detect refrigerant released from the sealed refrigeration system.
Identify that a sensor mounted within or near the indoor coil may be a required part of the equipment safety system.
Recognize that the manufacturer determines the approved sensor position for the equipment configuration and installation orientation.
Avoid damaging, covering, contaminating, relocating, disconnecting, or substituting a refrigerant sensor without following the equipment manufacturer’s procedures.
Determine sensor requirements from the equipment nameplate, installation instructions, service information, and approved replacement-part information.
What Does A2L Mean?
Refrigerants are classified according to characteristics that include toxicity and flammability.
The letter A identifies the lower-toxicity classification. The 2L designation identifies refrigerants with lower flammability characteristics and a relatively low burning velocity compared with more highly flammable refrigerants.
A1
Lower toxicity and no flame propagation under the conditions used by the refrigerant safety classification.
A2L
Lower toxicity with lower flammability characteristics. A2L refrigerants are commonly described as mildly flammable.
A3
Lower toxicity with substantially greater flammability than A2L refrigerants.
A2L does not mean nonflammable. It also does not mean that an A2L refrigerant behaves like a highly flammable A3 refrigerant.
A2L Refrigerants in Modern Equipment
Modern residential and light-commercial air-conditioning equipment may use A2L refrigerants such as R-32 or R-454B.
The refrigerant used in the equipment must always be identified from the equipment nameplate and manufacturer information rather than assumed from the age, appearance, or type of system.
Older Equipment
Many systems encountered in the field use A1 refrigerants and may not contain the A2L safety features found in newer equipment.
Newer A2L Equipment
May include refrigerant detection and other equipment-specific safety provisions required by the equipment design and listing.
Read the Nameplate First
Before opening or servicing refrigeration equipment, identify the refrigerant and review the manufacturer’s service information.
Why Detect a Refrigerant Leak?
A sealed refrigeration system is designed to keep refrigerant contained within the tubing, coils, compressor, and other refrigeration components.
If refrigerant escapes from the system, vapor can enter the equipment cabinet or surrounding space.
When required by the equipment design, a refrigerant detection system provides a way to detect the presence of leaked refrigerant before the concentration becomes excessive.
Refrigerant Is Normally Contained
The refrigeration circuit is intended to remain sealed during normal operation.
A Leak Can Release Refrigerant
A failure at tubing, joints, coils, valves, or other refrigerant-containing components can allow refrigerant to escape.
The Sensor Detects Refrigerant
A refrigerant detector monitors the area in which it is installed for the refrigerant it is designed to detect.
If a refrigerant detector is part of the listed equipment, treat it as an important equipment safety component rather than an optional accessory.
Where Is the Leak Sensor Located?
There is no single sensor location that applies to every A2L air-conditioning system.
The sensor may be installed within the indoor coil cabinet, air handler, fan coil, furnace-coil assembly, or another manufacturer-specified location.
The approved position is determined by the equipment design, refrigerant, cabinet arrangement, airflow, installation orientation, and the location where leaking refrigerant is expected to collect or pass the sensor.
Factory-Installed Sensor
Some equipment is supplied with the refrigerant sensor already mounted in its approved location.
Installation-Specific Sensor Position
Some equipment configurations may require the sensor position or installation details to match the actual equipment orientation.
Do Not Choose the Location by Guesswork
Install or position a refrigerant sensor only according to the instructions for the specific equipment.
Equipment Orientation Can Matter
Earlier in this evaporator subsection we examined upflow, downflow, and horizontal coil arrangements.
Changing equipment orientation changes the physical relationship among the evaporator, drain pan, blower, cabinet, and surrounding air.
On equipment equipped with refrigerant detection, the approved sensor location may also depend on that orientation.
Upflow
Verify that the sensor is installed in the position specified for the approved upflow arrangement.
Downflow
Do not assume that a sensor location used for an upflow arrangement remains correct when equipment is installed downflow.
Horizontal
Follow the instructions for the actual horizontal orientation and cabinet arrangement.
Recognizing a Refrigerant Leak Sensor
A refrigerant sensor may be a relatively small electronic component mounted inside the equipment cabinet.
Its exact appearance varies by manufacturer. It may have an electrical connector, harness, mounting bracket, protective housing, or identification label.
Do Not Identify It by Appearance Alone
Modern equipment can contain temperature sensors, pressure sensors, humidity sensors, air-quality devices, and refrigerant sensors that may look similar.
Use the Equipment Documentation
Wiring diagrams, service literature, parts information, and installation instructions identify the component and its approved location.
Protect the Sensor During Service
Service work around an evaporator can involve coil cleaning, drain maintenance, refrigerant piping, insulation, cabinet work, and electrical service.
A refrigerant sensor located in this area must not be treated as an obstacle that can simply be moved out of the way.
Moving the sensor can prevent it from monitoring the location for which the equipment was designed.
Insulation, tape, debris, or other material can interfere with refrigerant reaching the sensing element.
Protect the sensor from inappropriate cleaners, coatings, solvents, water, and other materials during service.
A required refrigerant detector is part of the equipment safety system and should not be defeated to make equipment operate.
Use only replacement components approved for the particular equipment and refrigerant.
Use the manufacturer’s approved inspection or test procedure rather than intentionally introducing refrigerant into the space.
If the Sensor Requires Service
The appropriate service procedure depends on the equipment manufacturer and sensor design.
Identify the Equipment
Record the equipment model, serial number, and refrigerant.
Identify the Sensor
Use manufacturer service information to confirm that the component is the refrigerant leak sensor.
Follow the Approved Procedure
Use the manufacturer’s instructions for inspection, testing, replacement, mounting, and connection.
Verify Correct Installation
Confirm that the approved sensor is securely installed in the correct position for the equipment orientation.
Equipment Sensor vs. Service Leak Detector
The refrigerant sensor installed inside A2L equipment should not be confused with a portable electronic leak detector used by a technician to locate a refrigerant leak.
Equipment Refrigerant Sensor
Remains with the equipment and monitors the area for which the system was designed.
Portable Service Leak Detector
Is a technician’s diagnostic instrument used to search refrigeration components and piping for the location of a leak.
The equipment sensor detects refrigerant presence for the equipment safety system. A service leak detector helps the technician locate the actual source of a refrigerant leak.
Do Not Assume Every A2L System Is the Same
Not every A2L system uses the same refrigerant, refrigerant charge, evaporator configuration, sensor, sensor location, or safety arrangement.
Some equipment may require an integral refrigerant detection system while other equipment designs or applications may meet their requirements differently.
Equipment-Specific Information Takes Priority
Use the installation instructions, service literature, equipment markings, and approved replacement parts for the system being serviced.
What We Are Not Covering Here
A refrigerant detection system can interact with other equipment functions, but those control sequences belong in a controls and safety lesson rather than in this evaporator lesson.
A2L recognition, why refrigerant detection may be present, sensor identification, sensor location, protection during service, and use of manufacturer information.
Control-board logic, detailed mitigation sequences, relay operation, blower-control sequences, bypass procedures, or programming.
Think Like a Technician
When opening a modern indoor coil or air handler, do not assume that every small component near the evaporator can be moved, disconnected, or cleaned without consequence.
Identify the refrigerant from the equipment nameplate.
Determine whether the equipment includes a refrigerant detection system.
Locate the sensor using the manufacturer’s equipment documentation.
Protect the sensor when cleaning or servicing the evaporator and drain system.
Verify the approved sensor location if equipment orientation has been changed or the coil has been replaced.
Use the manufacturer’s approved procedure if sensor testing or replacement is required.
Put the Concepts Together
A2L refrigerants have lower flammability characteristics than more highly flammable refrigerants but are not classified as nonflammable.
Modern comfort-cooling equipment may use A2L refrigerants such as R-32 or R-454B.
Some A2L equipment includes an integral refrigerant detection system.
The refrigerant sensor may be located near the indoor evaporator or elsewhere within the equipment as specified by the manufacturer.
Sensor location can depend on equipment design and installation orientation.
A refrigerant sensor that is part of the equipment safety system should not be relocated, covered, bypassed, or replaced with an unapproved component.
The installed equipment sensor and the technician’s portable refrigerant leak detector perform different jobs.
Manufacturer instructions and equipment-specific information determine the correct service procedure.
Can You Explain A2L Refrigerant Leak Detection?
You should be able to answer these questions before continuing.
1. What does the A2L refrigerant classification tell us?
2. Does A2L mean that the refrigerant is nonflammable?
3. Name two A2L refrigerants that may be encountered in modern comfort-cooling equipment.
4. What is the purpose of a refrigerant leak sensor installed in HVAC equipment?
5. Is every A2L system required to use the same sensor and sensor location?
6. Why can equipment orientation affect sensor location?
7. Why should a refrigerant sensor not be relocated during evaporator service?
8. Why should cleaning chemicals and other contaminants be kept away from the sensor unless specifically approved?
9. What information should be used when a refrigerant sensor requires replacement?
10. What is the difference between an installed equipment refrigerant sensor and a technician’s portable leak detector?
What You Should Have Learned
A2L refrigerants have lower flammability characteristics but still require appropriate safety consideration.
Some equipment using A2L refrigerants includes refrigerant detection as part of the equipment safety design.
The correct sensor location is determined by the particular equipment and installation configuration.
Equipment orientation can affect the approved refrigerant sensor position.
A required refrigerant sensor is an equipment safety component and should be protected during service.
Refrigerant sensors should not be relocated, bypassed, covered, contaminated, or replaced with unapproved components.
A built-in refrigerant sensor is different from a portable service leak detector.
Manufacturer installation and service information governs sensor inspection, testing, location, and replacement.
Next: Indirect-Expansion Evaporators
Most of the evaporator examples so far have placed refrigerant directly inside the heat exchanger serving the conditioned air.
The next lesson examines systems in which refrigerant first cools a secondary fluid such as water or glycol, and that secondary fluid carries the cooling effect to another heat exchanger.
Refrigerant Cools the Fluid · Fluid Carries the Heat