Air conditioner has a slow leak and I cannot find it?

There are two places these systems like to leak which are hard to find, first is the front seal of the compressor. This can be difficult because they leak a little when the system is not running and can leak more when the system is operating. You must use a leak detector at the front of the clutch down low with the system off (no wind or breeze), also look for compressor oil under the compressor which is a sure sign it is leaking. Next is the evaporator core, this will need to be done with a leak detector as well and must be near the condensation tube. This guide and video will help show you how:

https://youtu.be/yrhWKlQEPWw

and

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Please run down these guides and report back.