What is the yin function of Shen ?
There are likely many different ways to discuss such a general question, so perhaps you can be more clear on what it is you are trying to sort out. Generally speaking the shen, or “spirit/mind” is just that - a fixed entity in and of itself (no yin, no yang, per se). Imbalances in the body such as phlegm, empty-heat, etc. can affect the ability for it to clearly manifest but, in my understanding, it is never gone.
In technical terms it is related to the heart system (which can have issues such as heart yin deficiency - anxiety, palpitations, etc.) and it is said to be rooted in the blood (which is a yin substance) - influenced as well by the more yang substance (qi).
Again, if you can elaborate more on what you are trying to sort out, we could probably have a more direct discussion.