Freon – the technical name of the gas refrigerant in the AC – with time gets depleted and needs to be replenished in order for the AC to continue cooling. Hire the best Pros for the job now!. The PRO accurately determine the coolant level in the AC unit using a pressure gauge. If the level of gas, also called refrigerant is found below the normal PRO suggests a refill or top-up as per requirement. To start the coolant recharge, first the AC unit is shut down. Thereafter the gauge hoses are attached to the pressure port of AC unit. The AC unit is then turned on and allowed to run for 10 min so that it can reach a stable state of operation. Following it the valves of the refrigerant container (with container in the upright position) is connected to the AC unit. Now the AC unit is ready to draw coolant.