The process waits in this state until the call for heat is satisfied, the thermostat input is opened, or a fault occurs. When heat is satisfied, the sequence continues to Post-Purge and then back to Idle. If three tries for ignition has been selected on the MCB dipswitch and flame is not detected at the appropriate time, then the sequence moves to the Inter-Purge state for 15 seconds and the FCB heat sequence is repeated. If flame is still not detected after the third try the process declares a fault, jumps out of sequence and goes to the error state. Other types of faults detected at any time will also cause a jump to the error state.
Description of FCB control states:
•Idle State:
When any error is declared during idle state-The system will remain in this state until the MCB request a heating cycle, or a cold purge.
•Pre-Purge State:
The blower is turned on. After 10 to 34 seconds (34 seconds for cold purging) the system switches to the Heat Igniter State.
•Heat Igniter State:
The sequence of operation is as follows: “The igniter relay is energized and the heat up period begins. After 18-20 seconds, if the igniter has reached a minimum of 2.8 amps, the gas valve safety circuit is then activated. If in this amount of time, the igniter fails to reach a minimum amp draw of 2.8 amps, the unit will re-cycle up to 3 times before locking out on igniter hardware failure. If the igniter does reach the minimum required amp draw of 2.8 amps, the gas valve circuit is energized, and the system advances to Flame Check status.
•Check for Flame State:
The gas valve is turned on. After 1.5 seconds, the system checks that the gas valve relay is on. If it is not, the ignition trial is considered to have failed and the system advances to the Inter-Purge state, if any ignition trials remain, otherwise an error is declared.
The flame sensor is checked. If flame is detected, the igniter is turned off. The state machine then advances to the Heating
State. If after 5 seconds, the flame is still not sensed then the ignition trial is considered to have failed. The state machine advances to Inter-Purge if any ignition trials remain, otherwise an error is declared.
•Heating State:
The system remains in this state until the call for heat is cancelled or a fault occurs. The system returns to the Idle state if the call for heat is cancelled, or satisfied and to the appropriate fault state if a fault occur.
•Inter-Purge State:
The gas valve and the igniter are turned off. The blower is on. After approximately 15 seconds the system goes back to the Heating Igniter State.
•Post-Purge State
The gas valve and the igniter are turned off. If this stage does not have a blower the system returns to the idle state. If it does have a blower then the blower is left on. After approximately 25 seconds, the system returns to the Idle state.
•Error State
The gas valve and the igniter are turned off. The FCB micro tells the MCB micro which error has occurred. The system waits in this state until the MCB sends a command to clear the error, and the system returns to the idle state.
•Cold Purge State
Cold purge occurs when the MCB micro commands the blower to go on before lighting to clear the unit of residual gases. This state normally lasts approximately 32 seconds but on a special situation can last up to 5 minutes. If on the first call for heat after power up, blower prover switch is open, this state will take up to 5 minutes before declaring an error.
The MCB will wait the normal cold purge time (normally 32 seconds) before checking for activation of all active blower prover. If blower prover is active at this time the MCB cancels the cold purge request. After the first cold purge has been done a flag is set to prevent further activation of the shutter adjust 5 minute delay. Any further requests for cold purge will last the normal cold purge time. The FCB will go into fault mode if the blower prover does not activate after 15 seconds. This time allows the blower relay to activate, the blower to come up to speed, and the response from the blower prover to be filtered.
•User Settings Screen:
Each setpoint or user setting has either a limited selection of values, or a limited range of values. The Up/Down keys are used to change values. After changing an item, the Select key is pressed to accept the change, or the Menu key is pressed to reject the change and restore the item to its original value. The following setpoints can be changed:
•Operating Setpoint:
This setpoint sets the base temperature for the control algorithm.
OperatingSetpointAdjustmentProcedure
The system has a standard programmable Operating Setpoint range of 70°F (21°C) to 190°F (88°C) for a VW and of 70°F (21°C) to 220°F (104°C) for a VB for either a Remote or inlet probe depending on selection. The user can easily change the Operating Setpoint at any time by using the following procedure. When any configuration or setpoint is changed (and the Select key touched), the new value is IMMEDIATELY saved to non-volatile memory. The factory default setting is 120°F (49°C).
1.Press the MENU key.
2.Scroll the “>” with the DOWN key next to the USER SETTING
SCREEN.
3.Press the SELECT key.
4.Scroll the “>” with the DOWN key until it is pointing to
OPERATING SETPOINT.
5.Press the SELECT key.
6.Use the UP or DOWN key to select the value you wish to enter.
7.Press the SELECT key to accept and store the new value.
•High Limit:
The outlet temperature probe contains both an ECO switch and a thermistor for temperature measurement. The sensed outlet temperature is used for the automatically resettable High Limit setpoint. If the sensed outlet temperature exceeds the
High Limit setpoint, a “soft lockout” condition will occur and the burner will be shut off. This fault condition is automatically cleared when the temperature drops below the high limit setpoint minus the high limit differential.
AUTO HIGH LIMIT SETPOINT ADJUSTMENT PROCEDURE/ OUTLET TEMPERATURE PROBE
The High Limit setpoint has a range of 90°F (32°C) to 210°F (99°C) for a VW and a range of 90° (32°C) to 235°F (113°C) for a VB.
