If you log into the secured site, there is a FAQ which defines transactions which are required to be screened for 314a compliance. It's been a while since I reviewed it, but I believe Devs is correct in that ACH does not need to be screened.
You're not required to scan any party against OFAC's SDN List. OFAC screening is risk based and your OFAC RA or other appropriate document should detail who and how you will screen.
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"100 victories in 100 battles isnt the most skillful. Subduing the other's military w/o battle is the most skillful." Sun-Tzu