Performed preventative maintenance for 2 split systems. One system is in the basement and the other is in the attic. Each systems takes a Merv 11 air filter (16x25x5) which customer opted to replace through us. Did not have the proper size filters available during service. We can return with them when we come to do the leak investigation. Inspected all the electrical components. Confirmed proper high and low voltages. Tested the amp draw for the compressors, blowers and fan motors. Tested the temperature split between the supply and return for both. Basement system is operating at a 0° differential and the second floor system is operating at a 19° differential. After finding no temperature difference for the basement system I then put my gauges on to test the pressures. This system had no pressure in it at all. This is a sign of a major leak. Customer wants to move forward with leak investigation and Merv filters. Will need to return to do a leak investigation on the basement system.