Service Manual -
HRG18xxS1P
508206-01
Issue 2140
Page 26 of 83
time spend in defrost (defrost time). The outdoor unit control
monitors ambient temperature, outdoor coil temperature
along with the compressor run time in heating mode
and defrost cycle time. The outdoor unit control monitors
compressor run time in the heating mode when the
outdoor coil temperature is below 35°F and accumulates
the frost accumulation time. Once the frost accumulation
time is met the unit control will initiate a defrost cycle. The
unit will run in the defrost mode until the coil temperature
reaches the defrost termination temperature setpoint. The
maximum length of defrost cycle is 14 minutes and the
defrost cycle will automatically be terminated if the defrost
cycle exceeds 14 minutes.
Two consecutive low pressure switch trips while operating
in the heat pump heating mode will initiate a defrost cycle
to defrost that may occur during a weather related event
such as freezing rain.
Frost Accumulation Time
The frost accumulation time is the amount of time the
heat pump runs in the heating mode when the outdoor
coil temperature is below 35°F. The initial target frost
accumulation time is 90 minutes, but the control will adjust
the frost accumulation time higher or lower based upon
the previous defrost cycle time history. If the defrost cycle
time is short (80% or less of the defrost cycle time) the
defrost accumulation time will be increased by 30 minutes.
If the defrost cycle time is long (120% or more of the target
defrost cycle time) the defrost accumulation time will be
decreased by 30 minutes. If the defrost accumulation time
is significantly longer (200% or more of the target defrost
cycle time) or if the defrost terminates at the 14-minute
maximum time, the frost accumulation time is set to 30
minutes. No change is he frost accumulation time is made
if the frost accumulation time is close to the target defrost
cycle time (between 80% and 120% of the target defrost
cycle time.
Defrost Cycle Time
The defrost cycle time is the amount of time the unit
operates in the defrost mode from the point the defrost
cycle was initiated until the coil temperature reaches 50°F
regardless of defrost termination temperature setpoint.
The demand defrost control target defrost cycle time is
unique for each HRG18 heat pump model. The target
defrost cycle time of HRG1824S1P is 120s,
HRG1836S1P is 125s, HRG1848S1P is 130s,
HRG1860S1P is 135s.
Defrost Termination Temperature
The defrost termination temperature is adjustable on
the unit control using the jumper pins.
The defrost termination setting selections are 50, 70,
90 and 100°F. The factory default setting is 50°F
(10°C). The defrost termination temperature is
monitored by the coil sensor which is located at the
outlet of the outdoor expansion valve. See Figure 16 for
details.
NOTE:
Colder climates may require a higher
defrost termination temperature setting to ensure the
outdoor coil
is cleared of frost during defrost. If the
outdoor coil is not
adequately cleared of frost, the heat
pump may experience reduced heating performance or
damage to the outdoor
coil from the buildup of ice on the
coil.
DEFROST TERMINATION
JUMPER
DEFROST TERMINATION
JUMPER
DEFROST COIL
SENSOR LOCATION
Figure 16.
