R-404A Retrofit Procedures

1. Record Baseline Data

It is desirable to record system performance data prior to retrofit to establish the normal operating conditions for the 

equipment. Data should include temperature and pressure measurements throughout the system, including the 

evaporator, compressor suction and discharge, condenser and expansion device. These measurements will be useful 

when adjusting the system with 404A during the retrofit.

2. Isolate R-502 Charge 

The R-502 charge should be isolated from the rest of the system by pumping it down into the receiver. If no receiver is 

present, the refrigerant must be removed from the system using a recovery machine capable of meeting or exceeding 

the required levels of evacuation. The charge must be collected in a recovery cylinder. DO NOT VENT THE 

REFRIGERANT. Knowing the recommended R-502 charge size for the system is helpful. If it is not known, weigh the 

entire amount of refrigerant removed. This amount can be used as a guide for the initial quantity of 404A to be charged 

into the system. 

3. Choose Compressor Lubricant 

Mineral oil or alkylbenzenes are typically used as the lubricants for R-502 compressors. But, to achieve miscibility of 

the 404A with the lubricant, a polyol ester must be used. Honeywell recommends using a polyol ester lubricant 

approved by the compressor manufacturer. Differences among polyol ester-based lubricants make it difficult to assume 

that they are interchangeable. Check with the compressor manufacturer for the correct viscosity grade and brand for the 

compressor in the system being retrofitted. 

4. Drain the Lubricant 

Since many small hermetic compressors do not have oil drains, removal of the compressor from the system may be 

necessary for draining the lubricant. The best point in the system to drain the lubricant is the suction line of the 

compressor. Small hand-operated pumps are available which permit insertion of a tube into the compressor access port 

for removal of the mineral oil without removing the compressor from the system. Remember that most of the oil must 

be removed from the system before adding the replacement lubricant. For larger systems, the oil should be drained 

from multiple points in the system. Particular attention should be paid to low spots around the evaporator where 

lubricant often collects. The oil also should be drained from oil separators and/or suction accumulators. 

5. Measuring Existing Lubricant 

Measure and record the volume of lubricant removed from the system. Compare this amount with the amount 

recommended by the manufacturer to ensure that the majority of lubricant has been removed. This volume also will be 

used as a guide to determine the amount of polyol ester lubricant to add in the next step. 

6. Recharge Compressor with Polyol Ester Lubricant 

Add to the compressor the same volume of polyol ester lubricant as the volume of oil drained in step 5. 
7. Reinstall the Compressor 

Reinstall the compressor following the standard service practices recommended by the manufacturer If an oil pump was 

used to remove the oil, remember to reseal the access port. 

8. Recharge the R-502 

If the system charge was pumped into the receiver, the balance of the system should be evacuated and then the receiver 

valves opened. If the original charge was collected in a recovery cylinder, the system should be evacuated and then 

recharged with the original R-502. It may be necessary to "top off” the refrigerant charge to compensate for the small 

amount lost in draining the oil. 

9. Run the Compressor 

Run the compressor with the polyol ester lubricant and the R-502 for at least 24 hours. Next, drain the polyol ester and 

recharge with fresh polyol ester. Check the lubricant that was drained. Be sure the residual oil content is below 5%. 

Test kits are available from several lubricant suppliers for this purpose. It usually requires about three changes to get 

the mineral oil or alkylbenzene content under 5%. 

10. Continue to Flush the System 

Repeat steps 4 through 9 until the residual oil content is below 5%. The lubricant that was removed from the 

compressors in the flushing procedure must be disposed of properly. 

11. Evaluate the Expansion Devices 

Most R-502 systems with any of the common expansion devices will operate satisfactorily with 404A; however, it may 

be necessary to adjust the superheat. Honeywell recommends consulting with the equipment manufacturer whenever 

possible. 

12. Replace the Filter Drier 

Following system maintenance, a recommended service practice is to replace the filter drier. There are two types of 

filter driers commonly used in refrigeration equipment— loose-fill and solid-core. Many, but not all, of the standard 

loose-fill and solid-core driers used with R-502 are compatible with 404A. Check with your wholesaler to make sure 

the replacement filter drier being used is compatible with 404A. 

13. Reconnect the System and Evacuate 

Use normal service practices to reconnect and evacuate the system. To remove air and other non-condensibles, 

Honeywell recommends evacuating the system to a full vacuum of 1,000 microns or less from both sides of the system. 

However, attempting to evacuate a system with the pump connected to only the low side of the system will not 

adequately remove moisture and non-condensibles such as air. Use a good electronic gauge to measure the vacuum. An 

accurate reading cannot be made with a refrigeration gauge. 
14. Charge System with Honeywell 404A 

When charging the system with Honeywell 404A, it is important to remember that this product is a blend. For this 

reason, special charging procedures are required to ensure optimal system performance. It is essential when using 

Honeywell 404A that the system be liquid-charged by removing only liquid from the cylinder. Never charge the 

system with vapor from a Honeywell 404A cylinder. Vapor-charging Honeywell 404A may result in the wrong 

refrigerant composition and could damage the system. A throttling valve should be used to control the flow of 

refrigerant to the suction side to ensure that the liquid is converted to vapor prior to entering the system. NOTE: To 

prevent compressor damage, do not charge liquid into the suction line of the unit. Systems being charged with 404A 

require a smaller charge size than those using R-502. The charge typically will be about 85 percent by weight of the 

original R-502 charge with expansion-valve or optimized capillary systems. Honeywell recommends initially charging 

the system with 75 percent by weight of the original R-502 charge. For medium-temperature refrigeration applications, 

if the original R-502 charge was 100 pounds (50 Kg), initially charge 75 pounds (37.5 Kg) of 404A. If the original R502 charge was 300 grams, initially charge 225 grams of 404A. 

15. Check for System Leaks

Check the system for leaks using normal service practices. 

16. Check System Operation

Start the system and let conditions stabilize. If the system is undercharged, add additional 404A in increments of 5 

percent by weight of the original R- 502 charge. For example, if the original charge was 100 pounds (50 Kg), charge in 

increments of 5 pounds (2.5 Kg). If the original charge was 300 grams, charge in increments of 15 grams. Continue 

until desired operating conditions are achieved. Compressor suction pressures for 404A after stabilization should be 

within about 2 psi (15 kPa) of normal system operation with R-502 for most medium- and low-temperature systems. 

Compressor discharge pressures typically will be about 18-25 psi (125-270 kPa) higher than normal system operation 

with R-502. It may be necessary to reset the high pressure cutout to compensate for the higher discharge pressures of 

the 404A system. This procedure should be done carefully to avoid exceeding the recommended operating limits of the 

compressor and other system components. To avoid overcharging, it is best to charge the system by first measuring the 

operating conditions (including discharge and suction pressures, suction line temperature, compressor amps, superheat) 

before using the liquid-level sight glass as a guide. 

17. Label Components and System 

After retrofitting the system with 404A, label the system components to identify the type of refrigerant Honeywell 

404A) and specify type of polyol ester lubricant (including brand name) in the system. This will help ensure that the 

proper refrigerant and lubricant will be used to service the equipment in the future.