An AC unit not cooling enough. The Vent temps were a little high around 60F. Suction pressure was around 44. R22. Replaced duck work on boots as many connections were coming loose and leaking a little here and there. Shut the door to a room that was not part of the conditioned house which leaked air into the upstairs return at 85F. Liquid line had a some residue of oil through the concrete wall with no permigum but it only smelled of refrigerant slightly. Condenser is clean, A coil clean, filters clean, screening on EAC clean. Duct system is down flow into a collector box and to branch plenums with flex runs. For fun I threw about 1 pound of refrigerant in the system and of course I did this before fixing the airflow. Compound gauge read, 55 - 52 respectively and I buttoned up to get a new vent temp around 48F on a 72 degree - 78 degree day. My question is what caused the low suction pressure? The airflow, a small pinhole which hasn't been found, or is it possible a little bullet is getting milky? Unit is about 25 years old and next call it might be time to start dumping money into it or I might have another change out to do. SOO, what was the problem?