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Refrigerant Solutions Limited 

 

Appendix 8 

RS-50 (R442A)

RETROFIT PROCEDURE TO REPLACE R404A OR R507 

Replacing R404A or R507 with RS-50 essentially will follow the procedure specified by 

the equipment manufacturer for a refrigerant change. Since RS-50 is zeotropic it is very 

important that liquid, not vapour, refrigerant be added to the system. 

1. Ensure the right equipment is available, eg recovery unit and cylinders, container for 

recovered lubricant, vacuum pump, weighing scales, replacement drier etc. 

2. Before removing the R404A or R507A, operate the unit under standard operating 

conditions and record the pressures, temperatures and any other relevant measurable 

data to establish unit performance. Typically, the appropriate standard conditions for 

setting up the unit will have already been specified by the equipment supplier. 

3. Recover and weigh the R404A or R507A from the unit. The weight should be within 

the range specified by equipment manufacturer. 

4. Replace the filter/drier and evacuate the system. 

5. As in the case of R404A and R507, RS-50 should be used with a polyol ester 

lubricant. 

6. Before operating the unit, charge the unit with liquid RS-50. The weight added at this 

stage should be approximately 10% lower than the R404A or R507 charge specified 

by the equipment manufacturer. 

7. Operate the unit under conditions similar to those used in Step 2, closely watching the 

liquid line sight glass, the compressor oil level sight glass and the suction superheat. 

8. RS-50 has a lower liquid flow rate than R404A and R507, so that it may be necessary 

to close the expansion device relative to its setting for R404A or R507. 

9. The evaporator superheat should be checked and changed as necessary by adjusting 

the TX valve. 
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 Refrigerant Solutions Ltd 

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10. If liquid is observed in the suction line sight glass or the suction superheat is lower 

than required, close the TX valve further. If the equipment manufacturer recommends 

charging R404A or R507 by evaporator superheat or liquid sub-cooling, use the same 

amount of superheat or sub-cooling for RS-50 

11. If a liquid line sight-glass is fitted, charge to a full glass gradually adding more liquid 

RS-50 until only liquid is passing through the expansion valve. Do not overcharge 

the system.

12. Adjust the expansion device superheat setting as required. 

13. Check system thoroughly for leaks. 

14. Remove all R404A or R507A labels and clearly label system RS-50. 

Warning: It is highly recommended that the thermostatic expansion valve be checked 

and adjusted to compensate for small differences in the pressure temperature relationship 

of the replacement refrigerant when compared to the original refrigerant. Failure to check 

and adjust the valve could allow liquid refrigerant to enter the compressor and damage 

bearings and other compressor components.

RS SERIES OF REFRIGERANTS PRESSURE/TEMPERATURE CHARTS 

RS Series Pressure/Temperature charts indicate both liquid bubble point and vapour dew 

point of the RS Series Refrigerant. 

Liquid Bubble Point: this is the temperature which the liquid refrigerant will begin to 

vaporize at the given pressure. Below this temperature the liquid refrigerant will be subcooled. 

Vapour Dew Point: this is the temperature at which refrigerant vapour will begin to 

condense at the given pressure. Above this temperature the refrigerant vapour will be 

superheated. 

EvaporatorVapour Superheat:

To determine evaporator superheat, measure the suction line temperature at the outlet 

pipe of the evaporator and measure the suction pressure at the outlet pipe of the 

evaporator. Using the Pressure/Temperature chart, determine the vapour dew point for 

the measured suction pressure. Subtract the determined dew point from the actual 

temperature and this difference is the evaporator superheat. 
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 Refrigerant Solutions Ltd 

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Condenser Liquid Sub-Cooling:

To determine condenser sub-cooling, measure the temperature of the outlet pipe of the 

condenser and measure the condenser pressure at the outlet pipe of the condenser. Using 

the Pressure/Temperature chart, determine the liquid bubble point for the measured 

condenser pressure. Subtract the measured temperature from the determined bubble point 

and this difference is the condenser liquid sub-cooling.