Thank you for the reply. When the panel is in normal operation. (No alarm) the red light is lit/ON On the relay. My ac unit is wired through the normally open contacts. This tells me the coil is energized, closing my normally open contacts when there is no alarm.
That says the relay is operated in fail safe mode, which is constantly powered with the power dropped on alarm.
Since I don't know all the details of this system I have to make some educated guesses on its operation. It is possible that the AHU control relay is wired to a reverse polarity circuit that is being held turned ON in normal operation. When turned OFF in alarm the polarity would go back to the supervisory mode which would still have voltage at the relay terminals that cannot operate the relay.
I lifted some information from the datasheet you linked. It does state the relay is polarized for operation on a reverse polarity circuit. It is being done backwards in this system. It is possible that fail safe operation was in the job specifications and the FA tech used what he had available to make it work as specified to satisfy the engineer. In the picture below I drew an arrow to the diode on the board that makes it polarized. The banded end of CR2 is the cathode end of the diode which goes to the negative terminal. The diode conducts when the cathode is more negative than the anode end which allows the relay to energize.
One question. Is this a new installation or an update to an older site?