The Seasonal Energy Efficiency Ratio (SEER) rating of an air conditioning system is determined based on the entire system's efficiency, which includes both the outdoor condenser unit and the indoor air handler or evaporator coil. However, it is not accurate to claim that a 14 SEER condenser can magically become a 16 SEER unit solely because of the air handler and TXV (thermal expansion valve).
The SEER rating represents the cooling efficiency of the complete system, including both the outdoor and indoor components, as well as how they work together. The condenser and air handler are designed and tested as a matched system to achieve the stated SEER rating. While an efficient air handler and properly matched thermal expansion valve can enhance overall system performance, they cannot change the SEER rating of the condenser unit itself.
In this case, the Goodman GSXN406010AA is a 14 SEER air conditioner condenser, and the CHPT4860D4AA is a 4-5 ton air handler. The SEER rating for the entire system would be 14 SEER since that is the rating of the condenser unit. The air handler might help optimize the system's performance, but it doesn't change the SEER rating of the condenser.
It is crucial to verify the SEER rating of the entire system before purchasing, and you can ask your A/C professional for documentation or manufacturer specifications to confirm the SEER rating of the matched system they are proposing. If you have concerns about the information provided by your A/C professional, you might consider seeking a second opinion or consulting with another qualified HVAC technician for additional insights. Transparency and clear communication are essential when making significant purchases like an air conditioning system.