TdX 20 Retrofit Guidelines

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Bluon TdX 20 (R-458A) is an energy efficient, direct replacement for most direct expansion (DX) air conditioning (AC) and medium temperature refrigeration. Of the viable R-22 alternatives, only TdX 20 has zero ozone depletion potential (ODP), one of the lowest global warming potentials (1,564 GWP [AR5 standard]), like or better capacity (234 kJ/kg [R-22] versus 239 kJ/kg [TdX 20] latent heat of vaporization), and typically results in a short return on investment (ROI) making TdX 20 the most cost-efficient option of any R-22 alternative.

In most applications, Bluon TdX 20 requires little to no equipment modifications to the existing system, no oil change, and minor system tuning. The primary consideration when evaluating a TdX 20 conversion is that TdX 20 operates at lower pressures in relation to R-22 and certain pressure controls should be evaluated for appropriate set points – these controls might include the metering device(s), head pressure controls, pump down pressure controls, or other like pressure controls. Included in this app is a Pressure-Temperature Chart (PT Chart) for reference when making pressure set point adjustments.

Additionally, TdX 20 is a zeotropic blend meaning it has multiple constituents with multiple boiling points (i.e. temperature glide) which should be taken into consideration when making evaporator and condenser temperature set points, evaluating top-off procedures concerning leaks, and when charging a system. These topics will be discussed in greater detail under the “General Guidelines” section.


Bluon differentiates itself from other refrigerant manufacturers by striving to form a close partnership with its community of mechanical customers. Bluon is focused on providing as much information in a concise format to make the field technician’s life easier.

We accomplish that by maintaining open lines of communications with our highly experienced Technical Leads and Engineers as well as initiating our mechanical partners into our community through our Bluon Accreditation Program (BAP).

The BAP primarily serves as a refresher for the basics that play an intricate part of any conversion and provides assurance to the end-user that they are getting the best product and the best service. The BAP provides the mechanical access to Bluon’s many tools and resources, and a stamp of approval that Bluon backs your work with their industry only warranty.

Tier I Accreditation

Bluon Tier I Accreditation covers all package and split DX systems 20 tons and under. In order to become Tier I Accredited you must complete the 15-30 minute online training.

Most Tier I conversions are straightforward and simple conversions but it is the mechanical installer’s responsibility to refer to OEM guidelines on a case-by-case basis when evaluating TdX 20 as a retrofit option. For example, there are some smaller units that have fixed metering devices and large receivers which are not appropriate for any zeotropic blend per the manufacturer’s guidelines. Call Bluon Technical Support for more information.

Tier II Accreditation

Bluon Tier II Accreditation is for all DX split and package units over 20 tons. In larger systems, there are typically more pressure controls and adjustments that must be taken into consideration. Bluon requires all mechanicals who wish to convert these larger systems to become Tier I Accredited and to complete the first three (3) conversions with a Bluon Technical Lead onsite to provide consultation. The Bluon Technical Lead will work with the mechanical from the planning stage to the conversion to the final commissioning of the system to ensure the mechanical understands the nature of the TdX 20 refrigerant before converting large systems independently. Bluon reserves the right to change or adjust the accreditation process based on performance.

General Guidelines

Baseline System Operation (Tune)

Bluon TdX 20 was designed to operate within the original design parameters of the R-22 equipment.

Before converting any unit to TdX 20, proper unit operation should be understood and baselined for future reference when tuning TdX 20. Always refer to OEM recommendations when confirming proper system performance.


Verify proper airflow by checking filters, coils, and blowers. Indicate in the Pre-Inspection Checklist if the items need to be cleaned, repaired, or replaced. Confirm that the airflow is in accordance with OEM recommendations. If no OEM recommendations are available, generally nominal airflow is around 400 CFM per ton. Ensure dampers are opening properly; refer to OEM recommendations and the Pressure Controls section when tuning dampers to TdX 20 head pressures.

Design Temperature Difference (DTD)

The DTD determines what the condensing and evaporating temperatures and pressures should be when baselining proper system operation. If no OEM recommendations are available for DTD, typical evaporator DTD is around 35 ºF between the Return Air (RA) and evaporator temperatures. Condenser DTD depends on the system SEER but typically ranges from 20 ºF for higher SEER systems to 30 ºF for lower SEER systems. Use applicable refrigerant PT charts to convert the DTDs to respective pressures. These target pressures should be referenced when accessing proper system operation and later when charging and tuning the system post-conversion.


Confirm acceptable superheat at the evaporator coil outlet and at the compressor suction inlet. If no OEM recommendations are available, maintain a minimum 8-12 ºF superheat at the evaporator or a 12-20 ºF superheat at the compressor. If appropriate, maintain the original superheat set point once the unit is converted to TdX 20.

Superheat is important in maximizing the efficiency of the evaporator coil and in protecting the compressor by assuring no liquid refrigerant is making it back to the compressor. An ideal superheat set point balances between maximizing

evaporator efficiency while assuring the compressor is protected under the lowest potential load.


Subcool is important in assuring that there is a full column of liquid feeding the metering device. If no OEM recommendations are available, subcool should typically be between 8-12 ºF. Like superheat, subcool is an indicator of condenser performance. Ideal subcool maximizes condenser efficiency while maintaining a full column of liquid to the metering device under varying loads. Subcool should be measured between the condenser outlet or metering device inlet (typically at liquid line service port).

Pressure Controls

Bluon TdX 20 saves energy and extends equipment life by running at lower pressures and utilizing the coils more efficiently. Each system should be evaluated on a case-by-case basis to determine if the existing pressure controls are suitable for TdX 20 pressures, can be adjusted to TdX 20 pressures, or if the existing controls should be replaced. If the existing controls are not appropriate for TdX 20 pressures and need to be replaced, it is the installer’s responsibility to evaluate the economic viability of the project in their planning process. Pressure controls that utilize temperature inputs should not need adjusting with TdX 20.

In considering all pressure controls, there are important points to keep in mind:

TdX 20 operates at lower pressures;

TdX 20 has a 12 ºF theoretical glide;

The effective glide is closer to 7-9 ºF (due to flashing).

Conulting the OEM recommendations or referring to the set points established when baselining system performance, convert any pressure set points to temperature set points using the original refrigerant’s PT Chart (this may include cut-in and cut-out set points). Using the TdX 20 PT Chart, convert the temperature back to a pressure using the respective liquid and vapor pressures, whichever applies to the specific pressure control.

Example: An existing R-22 system has a low-pressure cut-out switch for pump down. The original set points are 35 psig cut-out (open) and 50 psig cut-in (closed). Referring to a R-22 PT Chart, 35 psig corresponds to approximately 12 ºF and a 50 psig pressure corresponds to approximately 26 ºF. Referring to the TdX 20 PT Chart, 12 ºF corresponds to a vapor pressure of 22.1 psig and 26 ºF corresponds to 34.8 psig.

An appropriate cut in/cut out pressure switch for this application would be 20 open/35 closed. If there is not a switch available at the specific pressures, chose a switch as close to the desired set points as possible.

Improper pressure control set points are the primary cause for a lack of energy savings after converting to TdX 20. Listed below are a few common pressure controls; this is not intended as comprehensive list but as a reference.

High Pressure Controls

Any head master controls, head pressure control valves, or similar pressure controls that maintain an artificially high head pressure should be evaluated and adjusted or replaced as needed.

Fan cycling controls are designed to maintain an appropriate head pressure in low ambient conditions and have cut-in and cut-out set points. Both set points should be converted using the previously discussed method to pressures that correspond to TdX 20. If the fan cycling controls are non-adjustable, they should be evaluated for appropriateness or replaced with the converted cut-in/cut-out set points.

Like fan cycling controls, dampers are used to maintain head pressure in low ambient conditions. Typically, dampers are actuated when the fan cycling controls are unable to maintain the head pressure. Damper set points can be adjustable or non-adjustable and may be refrigerant dependent. For non-adjustable controls, resistors can sometimes be installed to modify the damper opening position (refer to OEM guidelines).

If the condenser fan speed is controlled by variable speed drives (VFD’s) with pressure controls, the set point should be evaluated for TdX 20 pressures.

Low Pressure Controls

Like high-side pressure controls, low pressure controls can play an important part of proper system operation. Low pressure controls are often vital for ensuring proper oil return to the compressor, preventing liquid migration in the off cycle, preventing the compressors from pumping down into a vacuum, and many other safety mechanisms. Low pressure controls should be evaluated to ensure they are providing the same safety mechanisms as intended by the OEM.

A loss of charge switch is intended to protect the compressor from pumping down into a vacuum if refrigerant is lost to the point that the suction pressure cannot be maintained at a safe level. There should not be any changes necessary to the loss of charge set point with TdX 20.

Pump down systems are designed to move refrigerant from the low-pressure side to the high-pressure side where the refrigerant can safely condense in the off cycle. The two types of pump down systems are continuous and one-time. Both applications typically involve a liquid line solenoid valve that closes once the call for cooling has ended.

The compressor continues to run after the liquid line solenoid closes which moves refrigerant from the low-side to the high-side until a low-pressure cut-out is made. In a one-time pump down system, the compressors remain off until the next call for cooling. In continuous pump down, the compressors are brought back on if a cut-in pressure is made which keeps the low-pressure side between the two pressure set points, preventing off cycle refrigerant migration and refrigerant condensation.

Pump down systems can serve an additional purpose of ensuring proper oil return to the compressor(s). The pressure controls in pump down applications (cut-in and cut-out) should be evaluated and replicated as closely as possible to TdX 20 pressures using the previously discussed methods.

Unloaders are electrical or hydraulic controls used to regulate the capacity of the compressors to meet the cooling need under partial loads to reduce unnecessary power consumption. Unloaders using pressure controls will have to be adjusted to TdX 20 pressures. Check with the equipment manufacturer for proper adjustment methods.

Other capacity controls such as staging, multiple speed compressors, etc., should be evaluated on a case-by-case basis to determine suitability with TdX 20. As a general rule, pressure controls will need to be adjusted and temperature controls will be suitable.

Metering Devices

Most metering devices, if sized correctly for R-22, are appropriate for TdX 20 and should require only minor adjustments.

Fixed Metering Devices

Fixed metering devices such as capillary tubes, orifices and pistons should be charged to superheat. Superheat and subcool should be checked prior to converting to TdX 20 to establish the system baseline. Charge to OEM recommended superheat if available or refer to the previously discussed Superheat recommendations.

Once proper superheat is achieved, check system subcool (maybe lower than anticipated in fixed meter systems). Systems with fixed metering devices are typically critically charged meaning that the amount of refrigerant charged into the system is vital to the proper operation of the system and the safety of the compressor.

When charging critically charged systems, every ounce matters and charge should be slowly and intermittently added allowing the system time to stabilize after each adjustment. A general rule for charging critically charged systems is to only add one or two percent at a time and wait 15 minutes between each adjustment. It is also important to try to charge the system under a full load or charge the system to a safe condition and then properly tune the system when conditions are normal. For heat pumps, ensure proper superheat in both heating and cooling modes; if necessary, return to verify proper system operation under normal operation when conditions change.

Thermostatic Expansion Valves

Thermostatic Expansion Valves (also known as TEV’s or TXV’s) are mechanical metering devices that use a specific charge in the sensing bulb (depending on which refrigerant or types of refrigerants are being used) to modulate the nozzle opening to maintain a desired superheat set point under varying operating conditions.

Thermostatic Expansion Devices can be adjustable or non-adjustable. Adjustable TEV’s designed for R-22 typically require one to four turns closed (increasing superheat) when converting to TdX 20; other refrigerants (R-404A, R-507, etc.) may require the powerhead to be changed to R-22 or the valve replaced entirely. Consult with the manufacturer recommendations when choosing proper valves for TdX 20 applications.

When charging systems with adjustable TEV’s, charge to desired subcool then adjust superheat. Adjustments to the TEV (superheat) and charge (subcool) may have to be done iteratively until both desired superheat and subcool is achieved. Make minor incremental adjustments and allow system to stabilize before making additional adjustments.

Non-adjustable TEV’s on systems 5 tons and under can be charged as a fixed metering device (by superheat). In larger systems (over 5 tons), Bluon recommends converting or replacing non-adjustable TEV’s to adjustable TEV’s before installing TdX 20 for optimum efficiency, performance, and system safety. Please check the Bluon Mobile App for information specific to larger systems by model number.

Electronic Expansion Valves

Like TEV’s, Electronic Expansion Valves (also known as EEV’s or EXV’s) modulate the nozzle opening to maintain a constant superheat under varying loads, however, EEV’s use a motor within the valve to modulate the opening a given number of steps; the higher the number of steps the higher the resolution and control of the modulation. The valve is controlled by a driver and the driver must be programmed for the specific refrigerant being used to accurately modulate. Currently, Carel and Sporlan drivers have software programmed specifically for TdX 20 (listed as R-458A). Call Bluon Tech Support for more info.

Conversion Procedures

Tune – Upgrade – Optimize

The following procedures include what Bluon considers best practices but it is the mechanical’s responsibility to properly convert the system using industry best practices most suited for the specific situation.

Baseline System Operation (Tune)

The previously dedicated section describes this process in more detail but generally proper system suction pressures/temperatures, liquid line pressures/temperatures, superheat(s) (at evaporator and compressor), subcool, and amperage should be confirmed and recorded in the Pre-inspection sheet before converting any unit to TdX 20. Proper system operation can typically be assessed with these few simple readings.


EPA Section 608 prohibits the intentional release of any ozone depleting substance (generally CFCs and HCFCs) and dictates that qualified technicians make good faith efforts to maximize the recapture and recycling of CFCs and HCFCs. As R-22 prices continue to rise, correct recovery procedures will have increasingly higher cost benefits. It is therefore in the mechanical’s interest to implement the best practices possible when recovering refrigerant to maximize job profits, reduce equipment failures, and prevent unnecessary call-backs.

The utmost care should be taken to not introduce contaminants throughout the conversion process and proper refrigerant recovery is the first step to any proper retrofit; if done properly it can significantly reduce evacuation time and labor costs.

Before attempting to recover any refrigerant, first ensure that you have properly rated and approved equipment which should include recovery cylinder(s), recovery pump, hoses (recommend sight glass and inline filter), refrigerant scale (preferably digital), and typically a manifold gauge set or other applicable gauges.

It is also highly encouraged that valve core removal tools are utilized to (1) remove valve cores which will reduce recovery and evacuation time and (2) allow the system to be isolated during recovery to evacuation transition and when verifying proper evacuation. The size of the system, the allowable time for refrigerant recovery, and the ambient conditions should be accessed when determining which recovery method is most appropriate. It is also recommended that a thorough Leak Check is conducted, at least visually but preferably with a leak detection device, before any refrigerant is recovered from the system as this might reduce system downtime during conversion.

The two primary types of refrigerant recovery are vapor-liquid recovery and the push-pull method. For smaller systems (under 15 pounds of liquid refrigerant), the vapor-liquid recovery method is generally appropriate for recovering the refrigerant. However, for systems with more than 15 pounds of liquid refrigerant the push-pull method can be significantly faster than vapor-liquid recovery. Both processes are outlined below.

Vapor-Liquid Recovery:

  1. Ensure system and recovery equipment is off
  2. Place cylinder on scale
  3. Connect system liquid port to manifold high-side port
  4. Connect system vapor port to manifold low-side port
  5. Connect manifold utility port to the recovery equipment input port
  6. Connect hose from recovery equipment output to recovery cylinder vapor port
  7. Ensuring not to introduce non-condensables into system, purge all hoses
  8. Close all manifold valves
  9. Open recovery equipment output and input valves
  10. Open valve core removal tool ball valves and recovery cylinder vapor port
  11. Turn on recovery equipment
  12. Slowly open manifold high-side valve (do not fill cylinder more than 80% capacity)
  13. Once all liquid has been recovered, completely open manifold low-side valve
  14. Pull system into target vacuum of 15 in. Hg
  15. Close all valves and isolate systemTurn off recovery equipment and close output valve
  16. Close recovery equipment input valve and recovery cylinder vapor port
  17. Record weight of refrigerant recovered as this will be used for the TdX 20 charge

Push-Pull Recovery

  1. Ensure system and recovery equipment is off
  2. Place cylinder on scale
  3. Connect system vapor port to recovery equipment output port
  4. Connect system liquid port to recovery cylinder liquid port
  5. Connect recovery equipment input to the recovery cylinder vapor port
  6. Slowly open both recovery equipment valves
  7. Ensuring not to introduce non-condensables into system; purge all hoses
  8. Turn on recovery equipment
  9. Slowly open valves on recovery cylinder and system
  10. Once all liquid has been recovered, close all valves and isolate system
  11. The remaining vapor refrigerant can now be recovered using the standard Vapor-Liquid recovery methods previously described

Replace Filter Driers

It is recommended that before the system is opened, a small nitrogen charge is used to break the vacuum so that when the system is opened to atmosphere moisture and air is not pulled into the system. Any amount of moisture introduced to the system will significantly affect the evacuation time so special care should be taken to keep the system tight and dry.

Once the system is open, replace the filter drier with a manufacturer’s recommended filter drier that is rated for HFCs, ensuring the filter is oriented in the correct direction of flow; replace gaskets or seals as needed. Nitrogen should be purged through system during brazing to prevent contamination and the formation of copper oxides (will significantly reduce evacuation times and protect system).

Check Seals

When replacing any refrigerant with another refrigerant, some elastomer seals can react and expand differently causing leaks. Examples of such seals may include ball valves, Schrader core valves, gaskets, and some compressor shaft seals. Critical seals that can only be accessed with the system open should be closely evaluated and considered for seal replacement as a precautionary measure. Check non-critical seals and replace as needed.

Leak Check

There are three points at which leak checks should be conducted:

  1. A preliminary check before the refrigerant has been Recovered by visual inspection for oil spots or other signs of refrigerant leakage or using a leak detection device rated for the appropriate refrigerant
  2. A standing nitrogen pressure test once any modifications to the system piping have been made (filter driers, seals, metering devices, etc.)
  3. A standing vacuum test once the a proper Evacuation has been achieved

A standing nitrogen test is an easy method to quickly identify significant leaks. The amount the system is pressurized should be per manufacturer ratings but a general rule is to pressure test the system up to 150 psig in increments of 50 psig at a time, checking the system for audible leaks in between increments. Once the target pressure of 150 psig is reached, the system should be thoroughly checked with bubbles and allowed to stand anywhere from one to 24 hours depending on the system size and integrity of the line-set.

Some pressure fluctuations might be due to temperature swings during the standing pressure test but an easy calculation can be done to determine if the pressure swings are due to temperature swings or a leaky system. Using Equation (1), the anticipated final pressure can be determined and an assessment of the calculated pressure versus the actual pressure can be made to identify if the system has a potential leak.

Equation 1

Where P2 is the final pressure, T2 is the final line temperature, P1 was the initial pressure and T1 was the initial line temperature. All pressures and temperatures in Equation (1) must be in absolute (psig + 14.7; ºF + 459.7).

Doing a thorough nitrogen pressure test before the evacuation will reduce downtime if leaks are identified before the evacuation is started.


A sufficient evacuation is vital to ensuring the system is tight, dry, and free from non-condensables. A leaky system will eventually lead to a starving/inefficient evaporator; moisture in a system breaks down POE oil or will turn acidic with mineral oil leading to compressor failure; non-condensables will decrease system capacity, increase compressor wear and tear, and eventually lead to compressor failure. Proper evacuation can be time consuming but is far less painful than the resulting issues that will arise from an improper evacuation.

The time required to properly evacuate a system is largely a function of five things:

  1. Whether moisture, non-condensables, or other contaminants were introduced to the system during recovery
  2. The ambient conditions
  3. How tight and leak free the system is
  4. Techniques used during evacuation
  5. Equipment used for evacuation

If just a small amount of moisture is introduced into the system, the evacuation process will be significantly longer due to the intense amount of energy required to boil off the moisture. Some of the best methods for preventing the introduction of moisture or non-condensables into a system include meticulously purging hoses, breaking any vacuum with nitrogen before opening the system, minimizing the time the system is open, and by following good brazing techniques (particularly flowing nitrogen during brazing).

In the same way that moisture in a system extends the evacuation process, an improper recovery that leaves an excess amount of refrigerant in the system will prolong the evacuation; this is especially prevalent in low ambient conditions where the refrigerant can become trapped in pockets of oil and difficult to boil off.

In low ambient conditions, it is important to consider the possibility of desublimation or freezing during the evacuation process. Desublimation is when a substance changes directly from vapor to solid and during a deep vacuum in low ambient conditions there is an inherent risk of freezing moisture left in the system (either in liquid or vapor form).

If this occurs, it will be extremely difficult to remove the moisture from the system. The best way to avoid freezing moisture in the system is to avoid recovery and evacuation processes in low ambient conditions, however, if the conversion must be done in low ambient conditions the two best methods to remove ice from the system is to incrementally break the vacuum with nitrogen (i.e. triple evacuation) and by applying heat to the coldest parts of the system (particularly traps) as refrigerant will travel to the coldest regions. Do not apply an open flame to the system as refrigerant heated to much can turn acidic and lead to compressor failure.

If the evacuation is taking longer than anticipated, outside of the above considerations, there is either a leak in the system, inadequate equipment and/or improper procedures for the evacuation. Be sure to review the Leak Check and Check Seals section. Properly rated and appropriately sized equipment is crucial to a timely and proper evacuation. Below are a few things to keep in mind when selecting equipment for evacuation:

  • Ensure all equipment is properly rated for a deep vacuum; most manifold gauges are not
  • Use largest diameter hoses and ports available
  • Minimize connections and hose lengths as much as possible
  • Use Schrader Valve Core Removal Tools with isolation valves
  • Set-up connections so that the system can be valved off and isolated from hoses
  • Use high quality, accurate micron gauge
  • Install micron gauge as far from vacuum pump as possible (on other side of system if applicable)
  • Attach micron gauge directly to port or isolation valve so that readings can be made with system isolated
  • Chose appropriate size vacuum pump
  • General rule is rated CFM squared equals the size of the system (in tons)
  • Example: (10 CFM)2 = up to 100 Tons
  • Change vacuum pump oil after every use
  • Check proper vacuum pump operation prior to initiating evacuation
  • Attach micron gauge directly to pump
  • Ensure pump can pull down to at least 100 microns
  • If the pump does not pull down to 100 microns, try changing oil
  • If possible, it is better to use two smaller pumps on the high and low sides rather than one large pump
  • If pump is equipped with a ballast, keep ballast open until 10,000 microns is reached
  • Purge system with nitrogen as needed (see industry standard triple evacuation procedures)

The minimum recommendation for a properly evacuated a vacuum of 500 microns that does not rise more than 1000 microns in 15 minutes. If the vacuum continues to rise, there is a leak in the system. If the vacuum rises above 1000 microns and levels off, there is still moisture in the system and the evacuation should be continued. Once a proper evacuation is achieved, the system is ready to be charged.

Charge (Upgrade)

As with any other zeotropic blend, TdX 20 should be charged as a liquid only; meaning the cylinder should be inverted. Agitate the cylinder prior to charging to ensure the blend is properly mixed.

Initially charge the system to 80% of the original or recovered charge through an appropriate liquid line port. Once the initial 80% is charged and with the cylinder still inverted, slowly meter in liquid refrigerant into an appropriate suction port to bring the suction pressure up to start-up levels (recommended 35 psig); an inline sight glass will aid in this effort. Charging liquid refrigerant directly into the suction line will damage the compressor and may lead to compressor failure.

With the suction pressure at a safe startup level, bring the system online and allow it to stabilize (typically around 15 minutes).

Optimize System Performance

Once the system has stabilized, slowly and incrementally add charge to desire superheat and subcool levels. It is recommended that adjustments are made no more than every 15 minutes to allow system to stabilize between adjustments.

For Fixed Metering Devices, charge system to desired superheat. Desired superheat should be determined using the methods discussed in the DTD section based on the return air temperature. For adjustable metering devices (TEVs and EEVs), charge system to desired subcool and adjust metering device(s) to desired superheat. To completely dial the system in, adjustments will have to be by alternating between adding charge to bring subcool up (should reduce superheat) and adjusting the metering device to desired superheat; subcool should track with superheat response to metering device adjustments (e.g. as the metering device is opened, superheat decreases and subcool decreases, and vice versa). Getting superheat and subcool dialed in will ensure the system is operating as efficiently as possible while protecting the compressor under all operating conditions.

With superheat and subcool dialed in, confirm that all pressure controls are set to appropriate operating pressures. Allow the system stable run time to ensure proper operation, to take system readings, and to fill out the Commissioning Report.

Label Equipment

The final step for a successful TdX 20 conversion is properly and sufficiently labeling the converted system where the label is clearly visible and as protected from the elements as possible. Bluon recommends labeling the compressor and somewhere on the outside of the system at a minimum.

The mechanical may establish additional standards for clearly marking the equipment for follow-on technicians. Additional labels can be provided by contacting Bluon Technical Support.