What CFM (displacement) vacuum pump should I choose?

Match displacement to system volume: 4–6 CFM (about 7–10 m³/h) is fine for splits and small systems; 8–12 CFM suits larger commercial systems and long line sets. Higher CFM shortens the time to reach vacuum, but the ultimate vacuum level depends on the number of stages, not on displacement.

Single-stage or two-stage pump?

A two-stage pump reaches a deeper ultimate vacuum (typically below 15–25 microns) and is the HVAC/R standard, especially for moisture-sensitive R410A and A2L refrigerants. Single-stage is only adequate for simple jobs that don't require a deep vacuum.

Is the pump suitable for A2L refrigerants (R32, R454B)?

For A2L systems use a pump rated for flammable refrigerants — with a spark-free motor or manufacturer-approved for A2L. Always purge the system with nitrogen (OFN) beforehand and check the F-gas requirements for the refrigerant in question.