Read my post above yours. It had to leak somewhere. May have a slow leak in the schraeder valve fittings outside. The only way to know for sure it to remove all the freon and do an expensive pressure test with nitrogen. If it has not been serviced for several years it may lose 1 lb but to lose 2 sounds like a lot and I imagine the previous owner would not have tolerated poor heating or cooling. You can look at the outdoor sticker rating plate and it should tell you how many pounds and ounces it holds. 2 ton unit can hold up to 6 lbs so I am extrapolating.
The condo unit has been empty for about a year and the college students probably were comfortable by just lowering the stat.
Also, there is also the possibility that it did not really need 2 lbs of freon, not making an accusation but it is a possibility.
Here is more information from him:
York Heat Pump M# E1RC042S06D (2003 model)
Compressor pulling 12.8 out of 23.5
Evaporator York Air Handler M# F2FP048H06BS (2003 model)
Blower pulling 2.3 a out of 3.4
"Evaporator is clogged. Preassures read 65/150 psig on startup at 65 degrees. Due to clogged evaporator, pressures drop steadily into freezing range. Will not know how much freon is needed until evap coil is cleaned."