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Page 35
XP16 SERIES
Compressor Delay Mode (P5)
The demand defrost control has a field−selectable function
to reduce occasional sounds that may occur while the unit
is cycling in and out of the defrost mode. When a jumper is
installed on the DELAY pins, the compressor will be cycled
off for 30 seconds going in and out of the defrost mode.
Units are shipped with jumper installed on DELAY pins.
NOTE − The 30 second off cycle is NOT functional when
jumpering the TEST pins.
OPERATIONAL MODE OVERVIEW
The demand defrost control has three basic operational
modes. Those modes are:
1. Calibration Mode Ċ The demand defrost control is
considered uncalibrated when power is applied to the
demand defrost control, after cool mode operation, or
if the coil temperature exceeds the termination
temperature when it is in heat mode (see figure 26 for
further details).
2. Normal Mode Ċ The demand defrost control
monitors the O line, to determine the system operating
mode (heat/cool), outdoor ambient temperature, coil
temperature (outdoor coil) and compressor run time to
determine when a defrost cycle is required.
Calibration of the demand defrost control occurs after
a defrost cycle to ensure that there is no ice on the coil.
During calibration, the temperature of both the coil and
the ambient sensor are measured to establish the
temperature differential which is required to allow a
defrost cycle.
3. Defrost Mode Ċ The following paragraphs provide a
detailed description of the defrost system operation.
DEFROST CYCLE ACTUATION
The demand defrost control initiates a defrost cycle based
on either frost detection or time.
1. Frost Detection Ċ 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 demand defrost
control, a defrost cycle will be initiated.
2. Time Ċ If six 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
demand defrost control 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 demand defrost control logs the compressor run time.
If the demand defrost control 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 demand defrost control fails to calibrate, another
defrost cycle will be initiated after 45 minutes of heating
mode compressor run time. Once the demand defrost
control 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 six hours of heating mode
compressor run time has been logged since the last
defrost cycle.
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.