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Symbio 700 Demand Defrost Operation - derived from bench testing
First Defrost permit conditions after Power Up.
30 minutes run time with the Outdoor Air Temp less than 52° and the Outdoor Coil Temp less than 33°.
Subsequent Defrosts permit conditions.
Outdoor Air Temp less than 52°, Outdoor Coil Temp less than 33°, The New Initiate DT Value is reached.
To view the sensor temperatures using the Symbio 700 On-Board User Interface
Press Home, Down Arrow to Status
Press the Check Mark, then Down Arrow to System (for outdoor temp) or Refrigeration (for coil temp)
Press the Check Mark, then Down Arrow to “Outdoor Air Temperature Arbitrator” or “Coil Temperature
Sensor”.
Sequence of Operation
The first defrost after a power cycle will occur after 30 minutes of run time under defrost permit
conditions.
When the first defrost cycle has terminated, the board will track twelve (12) minutes to assure that a dry
coil condition has been achieved.
At the twelve-minute point, a Dry Coil Temperature Differential (DCTD) will be calculated using the
current values of OAT (outdoor air temp) minus OCT (outdoor coil temp).
Note: The OAT is expected to be higher than the OCT.
The (DCTD) value is then multiplied by 1.8 to calculate the New Initiate DT Value.
Once the New Initiate DT Value is reached, the next defrost cycle is initiated.
Defrost Termination
The defrost cycle is terminated when the Outdoor Coil Temperature (OCT) exceeds the Outdoor
Temperature (ODT) +47°F.
The defrost termination temperature (DTT) will be limited between 57°F and 72°F.
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