Been running my 94z convertible for years without air conditioning but recently have a little extra cash so decided to do a little restoration. The shop said the Freon level was 0 so added a few lbs of Freon and got it working. They put the unit on a pressure test but could not find a leak. They were quite sure there was one but again could not identify where it was coming from. They added red dye to help identify the problem. So I ran it for only a day or so when the cool became warm. So my question is why could they not find the breach with a pressure test and will they now be able to find the problem with the red dye? Is the problem most likely the condenser?

Thank you for your feedback as to what they should be looking for .