Unfortunately US versions of S3 and S4 has somehow limited support for two way call recording.
ACR is able to record on S3 with "workaround" option in it's settings enabled and recording delay set to 5-8 seconds.
If you are a S4 owner from US/CANADA you are out of luck. We weren't able to get ACR work .
This is not ACR's fault. Try any other call recording app from Play market and you'll see they don't work either.