Viconics HP727 - Manual (Page 12)

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10. DEFROST CYCLE SEQUENCE:
The HP727 has an evaporator temperature sensor to regulate the 3 speeds of the evaporator fan when the compressor operates. This
sensor is also used in the defrost cycle sequence.
The 3 speeds of the fan and the defrost cycle is controlled as follow.
Whenever the compressor starts, the evaporator fan speed will be at high for 10 seconds.
If the POL or SPA setpoints are superior to the water temperature by 10°F, the fan will operate in high speed only independently of
the defrost sensor temperature.
60 F 42 F 44 F 52 F 24 F
Evaporator temperature
Fan speed operation Defrost cycle operation
Low speed
Medium speed Medium speed
High speed Compressor still ON
Compressor OFF
Fan always at high speed
during defrost cycle
Low speed