Cant find leak in Lexus AC

I am total naive about car repairs. I have a 2001 Lexus RX 300 and it leaks freon for few summers now. Last year the mechanic replaced core. Few days ago I took it back to him and he has put “dye” and yet cannot see where the leak is. The mechanic is extraordinarily honest person, so I don’t want to leave him. I am here asking for suggestions as to where and what he should look for.
Thank you.

Topic

[Richard KirshyParticipant]

First thing would be to make sure the engine and engine bay is as clean as possible to allow best chance to see the dye.
If leak detection dye has been added, depending on the size of the leak it may take as little as a few minutes to a few weeks to show.
That is unless the leak is located with in the dashboard which would require it to be removed.

[Jeffrey VoightParticipant]

If the leak isn’t in the engine bay, it is most likely at the evaporator under the dash. You may have to gain access to it to find the leak, but before you do take a sample of the condensate that drips out from under the car and use a black light and them yellow glasses to determine if there may be dye present. If there is you found your leak.

[Author]

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