Page 22
d- Proper gas/air mixture is required for ignition on the
first attempt. If there is any deviation, within toler
ance of the unit, a second or third trial may be nec
essary for ignition. The control will lock out the
heating system if ignition is not obtained within
three trials and the (indoor) blower will not start.
Reset after lockout requires only breaking and re
making thermostat demand. See figure 20 for the
ignition attempt sequence with retrials (minimal
timings given for simplicity). Loss of flame during a
heating cycle is indicated by an absence of flame
signal. If this happens, the control will immediately
restart the ignition sequence and then lock out if
ignition is not gained within three trials.
e- The specific timings for the Fenwal ignition control
are shown in figure 21.
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
FIGURE 19
NORMAL IGNITION SEQUENCE
TIMINGS NOMINAL
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
GAS VALVE
IGNITION SPARK
BLOWER
IGNITION TRIAL
SECONDS 0 30 35 0 110
ON / CLOSED
OFF / OPEN
END OF
DEMAND
1
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
COMBUSTION AIR PROVE SWITCH
5 570
FIGURE 20
RETRIALS - IGNITION ATTEMPT SEQUENCE - TIMINGS NOMINAL
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
GAS VALVE
IGNITION SPARK
BLOWER
IGNITION TRIAL
SECONDS 0 30 35 70
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
65 100 105
RESET AT THERMO
STAT BY BREAKING DE
MAND
FENWAL LOCKOUT
COMBUSTION AIR PROVE SWITCH
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
5
FIGURE 21
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
THERMOSTAT DEMAND
COMBUSTION AIR BLOWER
GAS VALVE
IGNITION SPARK
BLOWER
IGNITION TRIAL
SECONDS 0 30
ON
OFF
FENWAL - IGNITION CONTROL TIMING
30
30
HEATING
CYCLE
6.8 (+3.4, -2.0) SEC.
END OF
THERMOSTAT
DEMAND
12 3
Blower starts 30 to 45 seconds after flame is sensed. When ignition occurs on any trial, the heating cycle begins. Ignition spark remains on for a total of 6.8 +3.4, -2.0 seconds from
the beginning of the trial period. If the flame sensor detects loss of flame during the heating cycle, gas valve remains open and ignition spark begins for one second. If flame is detected
before the end of one second, spark stops and the heating cycle continues. If flame is not detected during the one second ignition retrial, the control cycles through the complete ignition
sequence before locking out.
110+20 sec.
To Next Page
Loading...