We have discussed the transition to HFO and lower-GWP refrigerants in several previous articles, covering both their advantages and limitations.
One topic that frequently comes up is the conversion from conventional HFC refrigerants to newer lower-GWP alternatives through a process known as Refrigerant Retrofit.
Today, Colder Solution takes a closer look at what refrigerant retrofit means and the key steps involved in preparing an existing refrigeration or air-conditioning system for a new refrigerant.
What Is a Refrigerant Retrofit?
A refrigerant retrofit is the process of modifying or upgrading an existing air-conditioning or refrigeration system so that it can operate with a different refrigerant.
The replacement refrigerant may offer:
- Lower Global Warming Potential (GWP)
- Improved environmental performance
- Better compliance with current regulations
- Potential energy-efficiency benefits
- Improved long-term refrigerant availability
The main objective is to allow the existing system to operate safely and efficiently with the new refrigerant while reducing environmental impact and supporting compliance with changing refrigerant regulations.
Why Is a Retrofit Necessary?
Changing refrigerant is not always as simple as removing the old refrigerant and charging a new one.
When converting from an existing HFC refrigerant to a newer lower-GWP refrigerant or HFO-based blend, such as R-452A or R-449A in suitable applications, the new refrigerant may have different characteristics from the original fluid.
These differences can include:
- Operating pressure
- Mass flow rate
- Refrigeration capacity
- Temperature glide
- Lubricant requirements
- Material compatibility
- Expansion valve requirements
- Compressor operating envelope
For this reason, a refrigerant should not automatically be treated as a drop-in replacement unless specifically approved by the refrigerant and equipment manufacturers.
A proper retrofit process helps ensure that the system continues to operate safely and reliably after the refrigerant change.
Before Starting a Refrigerant Retrofit
Before any retrofit work begins, the existing refrigeration system should be carefully evaluated.
This is one of the most important stages of the entire retrofit process.
A qualified refrigeration professional should inspect areas such as:
- Compressor condition and compatibility
- Existing refrigerant
- Compressor lubricant
- Expansion device
- Valves
- Seals and gaskets
- Filter drier
- Pressure controls
- Refrigerant piping
- Heat exchangers
- Existing system faults
- Refrigerant leakage
- System operating conditions
The objective is to determine whether the existing equipment can operate with the proposed refrigerant and whether any components need to be replaced, adjusted, or upgraded.
The refrigerant manufacturer's Retrofit Guide and equipment manufacturer's recommendations should always be reviewed before carrying out the conversion.
Step-by-Step Refrigerant Retrofit Process
1. Recover the Existing Refrigerant
The first step is Refrigerant Recovery.
The existing refrigerant should be completely recovered from the system using appropriate recovery equipment.
It is also important to record the amount of refrigerant removed from the system.
This information can be useful when determining the initial charge quantity for the replacement refrigerant and evaluating the condition of the original system.
Recovered refrigerant should be handled, stored, reclaimed, recycled, or disposed of according to applicable regulations and procedures.
2. Inspect and Replace Components as Required
Components such as seals, gaskets, valves, and expansion devices should be inspected for compatibility with the replacement refrigerant and lubricant.
Depending on the refrigerant and system condition, it may be necessary to:
- Replace deteriorated seals
- Replace incompatible O-rings or gaskets
- Adjust or replace the expansion valve
- Replace the filter drier
- Inspect solenoid valves
- Inspect pressure controls
- Check elastomer compatibility
- Inspect service valves and fittings
Not every retrofit requires all of these components to be replaced.
The actual requirements depend on the original refrigerant, replacement refrigerant, lubricant, equipment design, and manufacturer recommendations.
Check the Compressor Lubricant
Lubricant compatibility is particularly important.
Some refrigerant conversions may require:
- Changing the oil type
- Removing residual mineral oil
- Changing to POE lubricant
- Performing multiple oil changes
- Checking lubricant viscosity
Always follow the compressor manufacturer's lubricant requirements.
3. Evacuate the System
After the system has been prepared, perform a proper vacuum evacuation.
The purpose is to remove:
- Air
- Moisture
- Non-condensable gases
Moisture and air remaining inside the refrigeration circuit can cause problems such as:
- Abnormally high pressure
- Reduced efficiency
- Acid formation
- Corrosion
- Lubricant degradation
- Compressor damage
The evacuation procedure and target vacuum level should follow accepted refrigeration practices and manufacturer recommendations.
4. Charge the New Refrigerant
Once the system has been properly evacuated, the new refrigerant can be charged.
The required charge quantity may not be identical to the original refrigerant charge.
Always use the refrigerant manufacturer's recommended starting charge and charging procedure.
For zeotropic refrigerant blends, the refrigerant is generally charged in the liquid phase to help maintain the correct blend composition.
The system should then be operated and fine-tuned according to actual operating conditions.
5. Adjust the Expansion Valve and Pressure Controls
A replacement refrigerant may have different pressure-temperature and mass-flow characteristics.
The system may therefore require adjustments to:
- Expansion valve
- Superheat setting
- Pressure switches
- Control setpoints
- Refrigerant flow
- Condensing controls
These adjustments help the system operate correctly with the thermodynamic characteristics of the new refrigerant.
Operating conditions such as suction pressure, discharge pressure, superheat, subcooling, compressor current, and discharge temperature should be checked during commissioning.
6. Perform Leak Testing and System Commissioning
After charging the new refrigerant, the system should be thoroughly tested.
Important checks include:
- Refrigerant leaks
- Suction pressure
- Discharge pressure
- Superheat
- Subcooling
- Compressor current
- Compressor discharge temperature
- Cooling capacity
- Energy consumption
- Oil level
- System stability
These measurements help confirm that the retrofit has been completed successfully and that the system is operating within an acceptable range.
7. Replace Equipment Labels and Record the Retrofit
Once the retrofit is complete, the system should be clearly relabeled.
The new label should identify important information such as:
- New refrigerant type
- Refrigerant charge quantity
- Lubricant type
- Date of retrofit
Maintenance and service records should also be updated.
This is particularly important because future technicians must know that the system no longer contains the refrigerant originally specified on the equipment nameplate.
What Should Be Checked After the Retrofit?
After the conversion has been completed, the system should be monitored to confirm that it continues to operate correctly.
Check for:
- Refrigerant leakage
- Abnormal pressures
- Abnormal compressor temperature
- Cooling capacity
- Energy performance
- Oil return
- Noise or vibration
- System control stability
A successful refrigerant retrofit is not simply one in which the new refrigerant can be charged into the system.
The objective is to ensure that the entire refrigeration system continues to operate safely, efficiently, and reliably over the long term.
Every Refrigerant Retrofit Is Different
The steps described above provide a general overview of a refrigerant retrofit.
However, the exact procedure can vary significantly depending on:
- Original refrigerant
- Replacement refrigerant
- Compressor type
- Lubricant
- Refrigeration application
- Existing system condition
- Expansion device
- Safety classification
- Equipment manufacturer requirements
For this reason, refrigerant conversion should always be carried out by qualified professionals and according to the Retrofit Guide, refrigerant supplier instructions, and equipment manufacturer recommendations.
A carefully planned retrofit can help the refrigeration system achieve good performance, maintain safety, and adapt to the transition toward lower-GWP refrigerants.
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