MAT-based anti-freeze protection is enabled when MAT temperature falls below the anti-freeze setpoint (3FRZ PROT). Note: MAT temperature may be obtained by an MAT, LAT (default) or automatically. The anti-freeze protection logic is the same no matter how the temperature is obtained.
If unit type is conventional unit and cooling/heating conventional operation mode is enabled:
- The compressor is closed.
- The damper either fully closes or opens to the minimum position (configurable using Parameter '3FREEZE POS' under Advanced Settings) regardless of occupancy status. If the damper is set to open to the minimum position, the actual opened position depends on CO2 sensor configuration:
- On the call of cooling when no CO2 sensor is configured, the actual minimum position is obtained from 2FAN L ACT. If a CO2 sensor is configured, it is from 2VENTMIN L.
- On the call of heating when no CO2 sensor is configured, the actual minimum position is obtained from 2FAN H ACT. If a CO2 sensor is configured, it is from 2VENTMIN H.
If unit type is heat pump and heat pump operation mode is enabled:
- The compressor is closed when there is cooling demand. On the call of heating, the controller opens the compressor.
- The damper behaves the same as the conventional operation mode. See the above for details.
DCV PID function doesn’t work during MAT-based anti-freeze protection.