Frymaster FBR18 Series manual Service Procedures, 6.1Functional Description

Ignition Wire Flame Sensor

25 V GND

HV

TD

Coil

FBR18 & FBRA18 SERIES GAS RETHERMALIZERS

CHAPTER 6: SERVICE PROCEDURES

6.1Functional Description

These rethermalizers contain a welded stainless steel cookpot that is directly heated by a high effi- ciency burner system requiring approximately 43% less energy than conventional burner systems to heat the same volume of water.

Two self-contained combustion chambers (referred to as “burners”) are located beneath the cookpot. Each combustion chamber is fitted with special ceramic tiles that are heated by the burning of a forced air/gas mixture. The tiles transfer their heat to the cookpot by means of infrared radiation, providing much more constant and uniform heat dispersion over the surface of the cookpot than do conventional burners. Because relatively less heat is lost to the atmosphere in the process, compared to “open-burner” designs, less fuel is required to achieve and maintain a given cookpot temperature.

Gas flow to both of the burners is regulated by one electromechanical gas valve.

THE ELECTRONIC IGNITION SYSTEM

Ignition modules, located in the component box, are	Inside the Ignition Module
connected to ignitor assemblies at each burner. An
ignition module performs four important functions: it	Out to
provides fuse protection for the 24-volt circuit, provides
	Gas Valve
an ignition spark, supplies voltage to the gas valve, and	To Alarm
proofs the burner flame. The module contains a 4-
second time delay circuit and a coil that activates the	25 V +
gas valve.

The ignitor assembly consists of a spark plug, an enrichment tube, and a flame sensor.

At start-up, the power switch is placed in the ON position, supplying approximately 12-volts DC to the heat control circuitry in the controller and to one side of the heat relay coil on the interface board. If resistance

in the temperature probe indicates the temperature in the cookpot is below 160ºF (71ºC), the current flows through a warm-up circuit containing a timer switch that alternately closes for 4 seconds and opens for 24 seconds. If the temperature is 160ºF (71ºC) or above, the current flows through a heat circuit, bypassing the timer switch. In either case, ground is supplied to the other leg of the heat re- lay coil, which then closes an electronic switch in the 24 VAC circuit to provide current to the igni- tion module.

Circuitry in the ignition module sends 24 VAC to the gas valve. Simultaneously, the module causes the ignitor to spark for 4 seconds to light the burner. A flame sensor verifies that the burner is lit by measuring the flow of microamps through the flame. If the burner does not light (or is extin-

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