Evaporator Defrost Control - Trane Symbio 700 Controller Application Manual

Evaporator Defrost Control

To prevent frost build-up on the indoor coil during low ambient conditions, compressor operation is
monitored and controlled accordingly, relative to outdoor air temperature.
Evaporator Defrost Control can be initiated through two means, based on the FroStat input.
FroStat Installed (default):
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Once the above two conditions are met, the FroStat Diagnostic will become Active.
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A FroStat input can also be used to directly request the Evaporator Defrost Control function
When the unit is running in an effective "Cool" mode, the FroStat input will directly control the
FroStat diagnostic. If the FroStat input CLOSES, the diagnostic will be annunciated.
When the unit is running in an effective "Heat" mode, and the Refrigeration System == Heat Pump,
the FroStat diagnostic will be controlled "Inactive" until the following are true:
– FroStat input is CLOSED
– One or More Compressors have been active for Heat Pump Heating for more than 30 seconds.
The FroStat diagnostic is an Auto-Reset diagnostic such that it will be reset when the FroStat input
is OPEN in either effecting unit mode.
If the FroStat diagnostic becomes active, the Compressor Output(s) will de-energize until the
FroStat diagnostic is cleared. The supply fan continues to operate during the FroStat diagnostic, so
long as it is still requested by a heating or cooling function.
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