When it comes to replacing R22 refrigerant for air conditioning, with a drop in or alternative refrigerant, there are many different options available. These options include but are not limited to R422D, R417A, R407C, R422B (Nu22), R427A, and R438A (mo99). The first and most important rule to drop ins or alternatives is that they must not be used to "top-off' the system. Mixing refrigerants in the field, is never recommended and actually illegal. If you are going to use a drop in or alternative for R22 in air conditioning, the system must be completely reclaimed of the previous refrigerant. In most cases an oil change is not required, as the replacement refrigerants are miscible with the oil that was typically used with R22 which was MO (mineral oil). 

It is imperative that your airflow is determined and set to 400cfm per ton, before continuing.

After you have decided the drop in or replacement you are going to use to replace R22, start by charging the system with approximately 90-95% of the original charge. For example, if the R22 system was originally charged with 8lbs (128oz), you would start with a charge of about 115-120oz. Allow the system to run for a minimum of 10 minutes to somewhat stabilize, then adjust the charge according to the required system superheat and/or subcooling. If the required superheat and subcooling is not available, a good baseline would be between 9-12 degrees for both superheat and subcooling.  

System performance with alternative refrigerants to R22,  will have around 95% capacity of what it did when using R22. The running pressures will vary somewhat, use your PT chart to determine this, we still want the evaporator coil approximately 40 degrees (35 degrees cooler than the return air). Example: R407C will be at 63psi to achieve a 40 degree evaporator. The condenser temperature or pressure should be set to achieve required subcooling, which should also give us approximately 25 degree CTOA (condensing temperature over ambient).  

So to review....

R22 Drop-In Replacements and Alternatives

Key Points Overview

1. Available R22 Alternatives

2. Important Guidelines for Using Alternatives

3. Airflow Requirement

4. Charging Procedure

5. System Performance Expectations

6. Pressure and Temperature Guidelines

1. Available R22 Alternatives

Common replacement refrigerants include:

• R422D

• R417A

• R407C

• R422B (Nu22)

• R427A

• R438A (MO99)

2. Important Guidelines for Using Alternatives

• Do NOT "top off" systems with alternative refrigerants.

  • Mixing refrigerants is unsafe, inefficient, and illegal.

• Systems must be completely reclaimed of the previous refrigerant before charging with an alternative.

• Oil changes are generally not required since most replacements are compatible with R22's standard MO (mineral oil).

3. Airflow Requirement

• Ensure airflow is set to 400 CFM per ton before proceeding.

4. Charging Procedure

• Start by charging the system with 90-95% of the original R22 charge.

  • Example: For an original charge of 8 lbs (128 oz), begin with 115-120 oz.

• Allow the system to run for 10 minutes to stabilize.

• Fine-tune the charge using the system's required superheat and/or subcooling values.

• If those values are unavailable, aim for a baseline of 9-12°F for both superheat and subcooling.

5. System Performance Expectations

• Alternative refrigerants typically operate at 95% of R22’s original capacity.

• Running pressures may differ slightly — always consult a PT chart.

6. Pressure and Temperature Guidelines

• For evaporator performance:

  • Maintain evaporator coil temperature at 40°F (approximately 35°F cooler than return air).

  • Example: For R407C, set to 63 psi to achieve 40°F.

• For condenser performance:

  • Set the condenser pressure to achieve proper subcooling.

  • Target approximately 25°F CTOA (Condensing Temperature Over Ambient).