Taken from Carrier Catalouge
For Model :GWRAC012ER030
Cooling Capacity* Btu/Hr 12600
Cooling Input Power* Watts 1197
Conversion Factor for Cooling Capacity of 1 Btu/Hour = 0.29307107 watts
So Cooling Capacity of this Airconditioner is = 12600X0.29307107=3692.7 W
EER= Cooling Cap in W/ Input Power in W= 3692.7/1197=3.084
Hope above is clear - the same can be done for other models also.
Note that the above figs are for the designed Capacity. In case of an inverter model the power drawn by the compressor varies depending on the load - goes higher at start condition and reduces when the room cools. The cooling capacity also varies accordingly though not in an exact linear fashion. It will be a safe assumption that the EER will be lower at other loads for the same Air conditioner.
I am not an expert however in brief the Invertor Air Conditioner has a variable speed A.C Motor ( Not a DC motor) which draws power based on the cooling load.
See below wiki link for a very brief explanation.
Air conditioner inverter - Wikipedia, the free encyclopedia