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START DEFROST
STATE
ACCUMULATE FROST
ACCUMULATION TIME – HP RUN
TIME IF COIL TEMP BELOW 35°F
INITIATE DEFROST CYCLE IF
FROST ACCUMULATION TIME
EXCEEDS TARGET FROST
ACCUMULATION
TIME (INITIALLY 90 MIN.)
DEFROST CYCLE WILL RUN AND
THE TIME IS COMPARED TO
TARGET DEFROST CYCLE TIME
(100S/133S/105S/102S)
DEFROST CYCLE TIME WILL BE
MEASURED UNTIL COIL TEMP
REACHES 50°F
DEFROST WILL TERMINATE
WHEN COIL TEMP REACHES
TERMINATION TEMP
RETURN TO HP HEATING
AND RESET RUN TIMER
Figure 28. Demand Defrost Cycle – Sequence of Operation
IF DEFROST CYCLE TIME IS
CLOSE TO TARGET DEFROST
CYCLE TIME (BETWEEN
80% - 120% TARGET DEFROST
CYCLE TIME) – NO CHANGE IN
FROST ACCUMULATION TIME
IF DEFROST CYCLE TIME IS
SHORT (80% OR LESS OF
TARGET DEFROST CYCLE TIME)
– FROST ACCUMULATION TIME
INCREASED BY 30 MIN.
IF DEFROST CYCLE TIME IS
LONG (120% OR MORE OF
TARGET DEFROST CYCLE TIME)
– FROST ACCUMULATION TIME
DECREASED BY 30 MIN.
IF DEFROST CYCLE TIME IS
SIGNIFICANTLY LONGER (200%
OR MORE OF TARGET
DEFROST CYCLE TIME)
OR TERMINATES AT 14m MAX
TIME – FROST ACCUMULATION
TIME IS SET TO 30 MIN.
31-5000750 Rev. 1
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