My AC unit runs constantly, slightly cool air comes from registers, to get the house cool I have to set themostat to a real low setting, I replaced the filter, I vacuumed out the inside coil, now the system is just barely working, one repair tech showed me that the issue is with freon leaks on the unit with a leak detector and oil residue on the unt, another ac tech said leak detectors don't work and that my unit is working if the lines are cold, which one is correct?

Dear leonard_dugan

Put your money on the first repair tech ! Freon leak detectors are real and working ! What you describe is typical for a freon leak. The problem is more : is the unit worth repairing (you didn't provide details on the unit itself). It's not just adding new freon. What is important is : is it possible to stop the leak properly? And will that repair be durable ?

Success!