From this post on the AMSAT.ORG website: http://www.amsat.org/?p=4726
"Probably the most notable observations about AO-85 are an apparent lack of sensitivity and difficulty in turning on the repeater with the 67 Hz CTCSS when it is not yet activated, or holding it on by the presence of the CTCSS. We have determined a probable cause for the sensitivity issue and while that can’t be fixed on AO-85 we are taking steps to prevent similar issues on the rest of the Fox-1 CubeSats. The tone detection threshold along with the receive sensitivity issue makes it hard to bring up the repeater."
But like Bill said, you aren't wasting your time -- you will just find it harder to work through AO-85 than SO-50. Trying to work it with low power and linear antennas when it is low on the horizon won't be a great return on the time invested.
On the other hand, if you can't hear it then perhaps you have other RX issues -- AO-85's TX signal is quite strong (the voice ID will be picked up even without other activity).
73, Bob, WB4SON