First, not to overlook the obvious, I'm assuming that in compressor-off mode it behaves appropriately. On monovalve cars like my '89, one cause for less-than-frigid AC is that the monovalve is sticking and the AC is cooling heated air rather than ambient-temp air.
Assuming that everything other than the compressor-evaporator area is OK, half the job was done earlier, but not the other half. Charging with the fluorescent leak tracer is good, but it's only informative if someone looks for the tracer a few weeks later--and from what you're saying, I assume there must be a leak. After all, if there's no leak, there's no need to recharge. Before doing anything else, I'd try to get the system recharged with tracer and then hunt around looking for the leak. If it's a slow leak, it may take a few weeks to show up.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)