The A/ENT-CTRL and A/DIFF-ENT are enthalpy controllers are used to monitor indoor and outdoor temperature and humidity before converting them into a relay output with the 24 VAC/VDC supply voltage sourced through the relay contacts when reaching its internal trip points. The supply voltage to the A/ENT-CTRL or A/DIFF-ENT is common to both the N/O or N/C contacts of the 10A Form C relay. The A/ENT-CTRL-F1C’s version includes a dry contact closure or switch instead of sourcing the supply voltage through the relay contacts.