SEER ratings are Fake News.
Let me explain.
Many sales people will sell you an AC unit with a high SEER rating and will tell you your system will achieve that rating. That is not necessarily true.
SEER ratings are based on the entire indoor/outdoor system. The outdoor unit (AC Condenser, or the Heat Pump Condenser), the furnace and the evaporator coil.
These units combined make up the SEER rating for your system. So an AC unit with a 18 SEER rating paired with a lower rated furnace and coil will not achieve a 18 SEER rating.
In the same vein, installing a new AC unit with an old furnace/coil setup will never produce the publicized SEER rating.
To know for sure, you should Always ask for the AHRI certificate to verify your new system. (Air-Conditioning, Refrigeration and Heating Institute. )
If you have further questions or would like to know the current SEER rating of your heating and air conditioning system, please contact one of our Extreme Comfort Advisors for details.