3 of 4 corrected typo

When exactly should an avel (mourner) not be davennning before the amud

An avel (mourner) if possible should daven also before the amud (be the chazan) on weekday. But certain times of the year especially when tachanun is not said (but not every time) he should not become the chazan.

I find that the poskim are not very clear about this.