When exporting a pdf from illustrator it changes the color codes

[giuseppe_0328]

Hello guys,

After thinking i was going crazy, i realized every time i export a pdf from illustrator the colors are different. 
For example, i'm doing a design that needs to be 100%k, multiple artbords (that i export singularly), and it exports in other color codes. Same thing happens if i only export the resources.  I'm already working on CMYK, how can i solve this? It's for work and it really can't keep happening. It didn't always do this, just from a month or so.  First screen is how i save it for export, second what i find once exported. 
Please help, it's literally useless this way! 

[Doug A Roberts]

The second screenshot shows an RGB file. What export settings are you using?