Frymaster H55 Series Technical Reference Manual page 60

Oil Return Sensor (OIB)
Troubleshooting (Gas
Only)
The heated oil-return sensor prevents
dry fi ring of the frypot. It's energized
with line voltage when the controller
is powered on. The sensor is in series
with a 7-second time delay board in
the control box that provides 24VAC
to the gas valve. In the absence of oil,
the sensor heats to its 570°F setpoint,
which sets off a 4-second internal
relay (in an egg-shaped device
connected to the probe) to control its
temperature. The 4-second cycling of
the power disrupts the 7-second delay
relay board providing power to the gas
valve. The fryer can't heat without oil
in the vat.
McDonald's Fryer: The otherwise
unused basket lift relay controls the
coil that sends power to the heated
probe. Power goes out pin 7 on J1
(DV) or pin 7 on J3 (FV).
FilterQuick: A relay in the control box controls the coil that sends power to the heated probe.
Typical sensor-related failures:
• Low temp but no call for heat (heat light).
• Stuck in melt cycle with no call for heat.
If the controller doesn't exit melt cycle or
continues to display low temp and does not
heat, ensure that the gas supply, gas valve, and
other components are working properly. If no
heat lamp illuminates because no call for heat is
initiated, check for carbon buildup on the OIB
sensor.
• Power to oil sensor (from relay used
for basket lifts on other interface boards
K1(DV) or K4 (FV)). Check pin 7 on J1 (DV) or pin 7 on J3 (FV) for 120VAC.
• Power to heater/relay coil on relay board. Check voltage to the coil on pins 8 and 1 to
ensure that 120VAC is present with oil in the vat. If the vat is empty, the power will
Automatic Filtering Fryers
The oil return sensor is controlled by a small board and the
electronics inside the egg-shaped device shown above.
The board is in the control box; the "egg" is near the probe.
The basket lift relay is used to close the coil on the OIB
board in the McDonald's unit above. A relay in the box (ar-
row below) controls the coil on the board in a FilterQuick
gas fryer.
Regular cleaning of the Oil is Back sensor
is critical. Insulating oil residue affects its
operation and oil won't return to the frypot.
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