I had the same issues when my evaporator went out, couldnt find a leak anywhere. Since you already have the UV dye in there, under the glovebox, remove the blower motor and blower resistor from the bottom of the HVAC box. Stick the light into where the blower motor goes and shine it toward the drivers side. You should be able to look up and into the HVAC box and see the evaporator from the hole where the blower resistor goes and spot any flourescent dye. You can also stick a camera/cameraphone into the box and take pictures of the evaporator and look for dye using the UV light and a regular flashlight/flash. If the evaporator is layered in dust, you probably have a leak there and it underneath the dust. If so, take a waterhose to it to remove the grime (it will drain out the condensate hole under the hood) and then i bet you can see all the dye.