Frymaster H55 Series Technical Reference Manual page 35

How Electric Fryers Work
E
lectric fryers with computer or electronic
controllers — 30 or 50lb or larger versions—
perform their oil heating tasks with the same
components as more advanced fryers with automatic
fi ltering and topping off functions. The fi ltering and
topping components are not involved in heating the
frypot.
How it Happens:
• The elements
operate on three-
phase and L1 and L3
provide line voltage
for the fryer's 12 and
24 volt transformers.
The 12 volt
transformer feeds the
controller. The 24-volt
transformer powers
the contactors.
• When the fryer is
turned on, 12VAC
is provided to the
controller, which
produces 12VDC
for the relays on the
interface board.
• The DC-operated
latch relay on the
interface board closes,
putting 24VAC on
the coil of the latch
contactor. Half of
the heating circuit is
closed.
• The hi-limit and the
drain safety switches
are both in the 24VAC
latch relay circuit.
• The controller monitors the temp probe and calls
for heat as needed.
• The 12VDC ground closes the relay on the
interface board, putting 24VAC on the heat
contactor's coil.
• Closing the heat contactor completes the circuit
made possible by the earlier closing of the latch
contactor. The element is energized.
Electric Fryers
• At setpoint, the heat relay on the interface
board opens, which removes 24VAC from the heat
contactor. The element is de-energized.
What Can Go Wrong
• Failure to properly clean the vat and its
components will cause the temperature probe to lose
sensitivity; the fryer can overheat.
• An element with an internal short can heat
continuously.
• An element with a pinhole will swell, oil leaks
into the element and air escapes. Smoke rises from
the oil, which is ruined by the failed element.
3-2
• A failed 12-volt
transformer will
deny power to the
controller, which
then can't provide
12VDC to the
interface board
for the operation
of the relays.
The relays won't
close. The fryer
won't heat.
• A failed 24-
volt transformer
means no power
to the latch or
heat contactor
coils.
• A failed coil in
the latch contactor
will prevent a
complete circuit
for the element.
• A stuck coil in
the heat contactor
will cause the
element to
overheat.
• A sticking relay
on the interface
board will cause
similar problems.