fwiw, i've never heard of it being necessary to add oil to anything except the compressor on an overhaul. But not an a/c guru.
Try calling Tom vdubnluvn in Winston perhaps ?
Any papers come with the new evaporator ?
Not saying this is 'wrong' section to post this to, but it might grab more eyes in troubleshooting or general section. I'm sure you're anxious for more knowledgable input.