Ac is the vowel “ah”
Anglo-Saxon Rune Poem (from ragweedforge.com)
Ac reversed signfies that qualities of endurance, stamina, faith and fidelity are lacking or being challenged today. The faltering oak tree, it cannot withstand any great blows or strike, and cannot keep strong against the challenges that are being faced. It has been a great many challenges so far, as well. Expect that nothing will last or endure today, and appreciate it for the moment that you have it.