Arrived on site to perform AC diagnostic on 2008 train condensing unit. Upon arrival Greg stated that the system was installed in 2015 by his buddy which is no longer available for service. He stated that his buddy that was working on the unit found a leak inside the evaporator coil but never got back to him for pricing on it. Began diagnostic at condenser and found that it was significantly low on R410a charge. At this time electrical checked out OK. Temperature split was only 2° differential indicating that the system was indeed. Advised Greg that recharging the unit will only result in it being low again in a unknown period of time due to us not knowing how big the leak is or where it is exactly located. Greg did decline a leak dye injection into the system and would only like to charge it up for this one time only. Charged approximately 5 pounds of refrigerant into the system and found that there was a pre-filter and a 5 inch filter which is not recommended for the systems airflow