RCV is a battery of measurements and calculations performed on your A/C system to insure that your system is operating at its peak efficiency and that you are not paying higher utility bills because of an improperly charged system.
First a little background on the issue.
The only way to insure that any air conditioning system is properly charged is to follow specific procedures that take into account many variables. These variables can include such things as the temperatures both inside and outside the structure, refrigerant saturation temperatures at both of the coils, airflow, humidity, configuration of the system and the temperature drop across the coils when running.
Over the years many HVAC contractors have invoked shortcuts that adversly effect your systems efficiency.
One widely used shortcut is the "beer can cold" method to charging a system. This involves dumping refrigerant into the system until the suction line becomes as cold as a good cold can of beer and presto, you're done.
Let's assume you paid for a 14 SEER system and your contractor is a beer can cold kind of guy. In all likelihood you are being left with a system that is (if you are lucky) a 10 SEER system. This means that you will now be paying a much higher utility bill than you should be paying. Yes, your system cools the home but you have no idea that the 14 SEER system you were sold is operating at 10 SEER or lower.
Having an independent third party inspector (a HERS rater) perform the RCV tests on your system after the contractor does his job both insures that the contractor is doing right by you and quantifies that your system is performing at it's peak efficiency. The job is not completed until the system passes the HERS (energy efficiency) tests and the building inspector will not sign off on the job without the HERS Certificate.