The Economizer Controller initiates the anti-freeze protection if MAT or OAT temperature falls below the anti-freeze setpoint.

If MAT and OAT sensors are connected to the Controller, both can trigger the anti-freeze protection independently. If the MAT sensor fails, MAT is substituted by OAT to continue the anti-freeze assessment. If OAT fails too, the controller either fully closes the damper or opens it to the minimum position based on occupancy status.

Once anti-freeze protection is enabled, alarm '4FREEZE ALARM' is generated and displayed on the HMI. Only if MAT and OAT temperatures increase to be 3 °F above the anti-freeze setpoint (3FRZ PROT) and OAT lockout setpoint (3OAT LOCK) respectively for one minute can the alarm be gone and the controller exit from the anti-freeze protection mode.