When I worked there the HR department did not listen to the employees at all and stood up for the management, even when your manager is the problem.
The proof of my statement is in the turnover rate for the department I worked in, compared to other departments. The turnover rate in my department was quite high, even when you put all departments together under the same manager.
The HR department when I left had a new VP department head and I believe he will do a better job than the one prior because he did not have the personal connections and he was willing to listen to me. He seemed to care about what I had to say. However, I cannot tell you what happened after I left or if anything changed at all.
I can tell you that I thought the new HR VP was a stand up guy, as was my department head.