Fujitsu FO20R Series Installation Instructions Manual page 32

Variable speed r-410a heat pump outdoor units
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6.0 NORMAL SEQUENCE OF OPERATION
5.
The indoor air-handler or gas furnace
is directed to supply supplemental heat
to prevent cold air from being discharged
from the supply registers during the
defrost cycle.
6.
The compressor speed is ramped to the
pre-determined defrost speed for the
duration of the defrost cycle.
Defrost Termination: The defrost cycle will
continue until the coil temperature has reached
the termination temperature or 14 minutes
have elapsed, whichever comes first. The
factory default termination temperature is 60°F
[15.6°C], although this temperature can be
changed to 40°F [4.4°C], 50°F [10°C], or 70°F
[21.1°C] using dip switches on the VSODC (see
chart below for dip switch settings). When
the coil temperature reaches the termination
temperature or 14 minutes have elapsed, the
following action is taken.
1.
The compressor speed is ramped to the
reversing valve switching speed for 30
seconds before the reversing valve is
energized.
2.
The reversing valve will be energized,
switching it back to the heating position.
3.
The outdoor fan motor is energized.
4.
Auxiliary heat is de-energized.
5.
The EXV will return to the normal
superheat control mode.
6.
The compressor speed will ramp to a pre-
determined oil circulation speed for 6
minutes.
7.
The system returns to normal heating
operation as directed by the Digital
Control Center.
NOTE: Should the outdoor ambient
temperature thermistor fail, the VSODC
will initiate a defrost every 34 minutes of
operation when the coil temperature is
below 35°F.
Off
On
Off
On
32
º
º
Off
60
F [15.6
C]
Off
50
º
F [10
º
C]
On
40
º
F [4.4
º
C]
º
º
On
70
F [21.1
C]
6.8 Sequence
of Operation for
Conventional 24VAC
Thermostat Controls
When the 20 SEER heat pump system is controlled
by a conventional 24VAC 2-stage thermostat rather
than the Digital Control Center, the system will
operate as follows:
The system will operate as a single-stage
system instead of a variable speed system.
When a call for cooling or heating is received
from the thermostat, the compressor will start
and operate at the nominal capacity level
and the air-handler will deliver the nominal
air-flow level. For dual fuel applications,the
variable speed gas furnace will deliver 100%
of the cooling air-flow level selected by dip
switches on the furnace control board. Y1 &
Y2 must be jumpered at the furnace control
board.
When the call for operation ends, the system
will shut down and remain in stand-by mode
until another call for operation occurs.
Demand defrost and low-ambient cooling
function normally.

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