507635-05
Page 17 of 22
Issue 2245
• Defrost Mode—
The following paragraphs provide a
detailed description of the defrost system operation.
Defrost Cycles
The control board initiates a defrost cycle based on either
frost detection or time.
• Frost Detection
—If the compressor runs longer than
30 minutes and the actual difference between the
clear coil and frosted coil temperatures exceeds the
maximum difference allowed by the control, a defrost
cycle will be initiated.
IMPORTANT
-
The control board will allow a greater
accumulation of frost and will initiate fewer defrost
cycles than a time/ temperature defrost system.
• Time
—If 6 hours of heating mode compressor run
time has elapsed since the last defrost cycle while the
coil temperature remains below 35°F (2°C), the control
board will initiate a defrost cycle.
Actuation
When the reversing valve is de-energized, the Y1 circuit is
energized, and the coil temperature is below 35°F (2°C),
the board logs the compressor run time. If the board is not
calibrated, a defrost cycle will be initiated after 30 minutes
of heating mode compressor run time. The control will
attempt to self-calibrate after this (and all other) defrost
cycle(s).
Calibration success depends on stable system
temperatures during the 20-minute calibration period. If
the board fails to calibrate, another defrost cycle will be
initiated after 45 minutes of heating mode compressor
run time. Once the control board is calibrated, it initiates
a demand defrost cycle when the difference between
the clear coil and frosted coil temperatures exceeds the
maximum difference allowed by the control OR after 6
hours of heating mode compressor run time has been
logged since the last defrost cycle.
NOTE:
If ambient or coil fault is detected, the board will not
execute the “TEST” mode.
Termination
The defrost cycle ends when the coil temperature exceeds
the termination temperature or after 14 minutes of defrost
operation. If the defrost is terminated by the 14-minute
timer, another defrost cycle will be initiated after 30 minutes
of run time.
5-Strike Lockout Feature
The internal control logic of the board counts the pressure
switch trips only while the Y1 (Input) line is active. If a
pressure switch opens and closes four times during a Y1
(Input), the control logic will reset the pressure switch trip
counter to zero at the end of the Y1 (Input). If the pressure
switch opens for a fifth time during the current Y1 (Input),
the control will enter a lockout condition.
The 5-strike pressure switch lockout condition can be reset
by cycling OFF the 24-volt power to the control board or by
shorting the TEST pins between 1 and 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while the Y1 Out line is engaged,
a 5-minute short cycle will occur after the switch closes.
