Manual
15
FRCC.ES.014.A6.22
Sequence of operation – Field wiring
Defrost Cycle
NOTE
1. The defrost cycle starts automatically by the
timer at predefined intervals. Typical settings
are between two and four defrost cycles per day
for freezers. For heavier frost loads additional
settings may be required.
2. Contacts “2” to “4” opens in the defrost timer and
disconnects the circuit to the room thermostat,
liquid line solenoid, and evaporator fan motors.
This will lead the compressor to pump down
and shut-off. At the same time, Contacts “1”
to “3” closes in the timer and it will allow the
defrost heater to start through the heater
contactor.
3. The defrost heaters rise the temperature of the
coil to 32˚F triggering the frost to melt of the
coil.
4. When the coil temperature rises to 45˚F to 55˚F,
the cycle limit switch closes and it energizes
the Liquid line solenoid valve to allow the
refrigeration cycle to begin again.
5. If the termination thermostat fails to close,
the fail-safe set on the timer will terminate the
defrost.
6. The defrost heaters are off.
7. The low-pressure control closes when the cut-in
pressure is attained, allows the compressor to
start.
8. When the evaporator coil temperature reaches
23˚F to 30˚F, the fan delay closes and allows the
fan motors to run.
9. The system will now operate in the refrigeration
cycle until another defrost cycle is triggered by
the timer.
This wiring diagram is for field reference only.
1) Two contactors one for evaporator fan and
other for defrost heater will be needed. No
extra contactors to be provided with the
unit.
2) Fuse F4 for defrost heaters and cable and
Fuse F5 for evaporator fans and cables will
not be supplied with the unit. These will
need to be purchased separately.