Frymaster Gas Rethermalizers FBKR18 Series - Manual (Page 34)

6-1
FBCR18 & FBKR18 SERIES GAS RETHERMALIZERS
CHAPTER 6: SERVICE PROCEDURES
6.1 Functional Description
These rethermalizers contain a welded stainless steel cookpot that is directly heated by a high
efficiency 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 connected to ignitor assemblies at each burner.
An ignition module performs four important functions: it provides fuse protection for the 24-volt
circuit, provides an ignition spark, supplies voltage to the gas valve, and proofs the burner flame.
The module contains a 4-second time delay circuit and a coil that activates the 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 or computer 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 180ºF (82ºC), the current flows through a circuit containing a timer switch that alternately
closes for 6 seconds and opens for 24 seconds. If the temperature is 180ºF (82ºC) 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 relay coil, which then closes an electronic switch in the 24 VAC circuit to
provide current to the ignition 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
extinguished), current to the ignition module is cut, preventing the main valve from opening, and the
ignition module “locks out” until the power switch is turned off and then back on.
A probe monitors the temperature in the cookpot. When the programmed setpoint temperature is
reached, resistance in the probe causes the heat cycle circuitry in the controller 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.