Need some help with where I'm supposed to put this thing. Small UV light that requires drilling so the lights sit inside the system.

The red arrow shows the coils. The green arrow is where I assumed the UV light would go (right after the coils). Plan was to drill a hole on top of the box just in front of the return duct heading up...

But when I drilled into that "box" there was at least 2 inches of insulation or filter material? So now I'm not sure where this thing is supposed to go. Any ideas?

UV light is pictured sitting on the furnace.

tia

I can't really help but the 2" you drilled through is probably duct board. They build plenums out of them sometimes. My UV light is completely INSIDE the unit and screwed to a metal part of the plenum with a little metal bracket holder thing. The only thing that comes out of the air handler is a little 12v wire for it. I think they can go a couple of places depending on what you want to protect. Mine is on the supply side with the blower so it protects the coil and drip pan. I think you can have them on the return side as well if you just want to sterilize everything. Mine works really well. The drip pan doesn't have a spec of mildew on it.

Makes sense

My concern is that the UV light is going to come into contact with something it shouldn't, and shorten the lifespan of….whatever it's coming in contact with (duct board)

Not sure where this thing should be placed with my set up.

It's a 2 ton unit and is the sole unit for an above garage room of 280 sq ft. There's a funny barn/musty smell in that room. (Just bought the house). AC guy said a UV light would fix it, but wanted to charge me $1900.

I refuse to let him win. Gotta figure this out

My UV light is 18" long or something and it's housed in a glass tube. Is yours a different design? Is the black box in the pic the whole unit?

The black box you see has two bulbs attached. About 8 inches long each. Hard to see in the photo

You put it on the downstream side of the coil usually about 8" or so behind it. The UV will cause your filter to disintegrate if you put the light upstream of it.

put it at your green arrow