Thermostats - Frymaster FilterQuick FQG80T Service Manual

At start-up, the power switch on the touchscreen controller is placed in the ON position, supplying approximately 24
VAC to the heat-control circuitry in the Smart Interface Board and to one side of the heat relay coils on the Smart
Interface Board. If the resistance in the temperature probe indicates the temperature in the frypot is below 180ºF
(82ºC), the melt cycle function is activated where a timer activates for six seconds and deactivates for 24 seconds. If
the temperature is 180ºF (82ºC) or above, the melt cycle is bypassed. In either case, ground is supplied to the other
leg of the heat relay coils, which closes electronic switches in the 24 VAC circuit to provide current to the ignition
module. Circuitry in the ignition module sends 24 VAC current to the gas valve via a normally closed high-limit
switch and a float safety switch. Simultaneously, the module causes the ignitor to spark for up to 90 seconds to
light the pilot flame. A flame sensor verifies that the pilot is lit by measuring the flow of microamps through the
flame. If the pilot does not light (or is extinguished), current to the ignition module is interrupted, preventing the
main valve from opening, and the ignition module "locks out" until the power switch is turned OFF, then back ON. A
probe monitors the temperature in the frypot. When the programmed setpoint temperature is reached, resistance
in the probe causes the heat cycle circuitry in the SIB board to cut off current flow through the heat relay. This in
turn cuts off the 24 VAC to the ignition module, causing the gas valve to close.
NOTE: Microamp readings on these black modules will move up and down as the module pulses on and off and
this is an indication that the module is functioning.
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Thermostats

A temperature probe monitors the temperature in the frypot. The probe resistance varies directly with the
temperature. As the temperature rises, resistance increases at a rate of approximately 2 ohms for every 1°F
(approximately 3.7 ohms for every 1°C). When the programmed setpoint temperature is reached, resistance in the
probe causes the heat cycle circuitry in the controller to interrupt current flow through the heat relay. This in turn
interrupts the 24 VAC current to the ignition module, resulting in closure of the gas valve.
Circuitry in the controller monitors the probe resistance and controls burner firing when the resistance exceeds or
falls below the programmed temperature or setpoint.
The fryers are also equipped with a high-limit thermostat. If the fryer fails to properly control the oil temperature,
the high-limit thermostat prevents the fryer from overheating to the flash point. The high-limit thermostat acts as a
normally closed power switch that opens when exposed to temperatures above 425ºF to 450ºF (218ºC to 232ºC).
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