SEER, or Seasonal Energy Efficiency Ratio, is a measure of the efficiency of an air conditioning system. It is calculated by dividing the cooling output of the system over a typical cooling season by the total electrical energy input during the same period. The higher the SEER rating, the more efficient the system is.

SEER 2 ratings are a type of modified SEER rating. Instead of using a typical cooling season to calculate the efficiency of the system, a SEER 2 rating uses a peak cooling season. This means that the rating takes into account the hottest days of the year, when the air conditioning system is likely to be running at its maximum capacity.

In general, SEER 2 ratings are considered to be more accurate than standard SEER ratings. This is because they take into account the conditions under which the system is likely to be operating at its highest level of efficiency. However, SEER 2 ratings are not as widely used as standard SEER ratings, and they may not be available for all air conditioning systems.

In conclusion, the main difference between SEER and SEER 2 ratings is the way that they are calculated. Standard SEER ratings use a typical cooling season to measure the efficiency of an air conditioning system, while SEER 2 ratings use a peak cooling season. SEER 2 ratings are considered to be more accurate, but they are not as widely available as standard SEER ratings.