I have a 24vac input, and want to use a NO relay so an arduino knows when the relay is closed
No relay is needed. You could rectify the 24V into DC, smooth it with a cap, then drive the input of an optoisolator with a proper current limit resistor.  When AC is applied the opto's open-collector output could pull a uC input with internal pullup resistor low to signal that AC is present.
Example part:
https://www.onsemi.com/pub/Collateral/HCPL2631M-D.pdf