3DJH
B--Early Model G24M Series With Ram Ignition Control
1 -- When disconnect is closed, 120V is routed through
door interlock switch (S51) to feed the line voltage
side of the furnace control (A3) and transformer T1
primary. Door interlock switch must be closed for
A3 and T1 to receive voltage.
2 -- T1 supplies 24VAC to terminal 24VAC on A3. In
turn, terminal R of A3 supplies 24VAC to termi-
nal RC of the indoor thermostat (not shown).
3 -- When there is a call for heat, W1 of the thermostat
energizes W of the furnace control with 24VAC.
4 -- CMB BLWR of the blower control energizes the
combustion air blower (B6). When the combustion
air blower nears full speed, combustion air prove
switch (S18) closes.
5 -- When S18 closes, assuming the flame rollout
switch (S47), primary limit (S10) and secondary
limits (S21) are closed, the furnace control begins
a 45 second time-delay (pre-purge).
6 -- At the end of the pre-purge cycle, the furnace con-
trol simultaneously opens the gas valve and sends
high voltage to the spark electrode.
7 -- When flame is sensed, the furnace control begins
a 45 second delay before energizing the indoor
blower.
8 -- When heat demand is satisfied, W1 of the thermo-
stat de-energizes W of the furnace control and the
furnace control immediately de-energizes the gas
valve. The combustion air blower runs for 5 se-
conds (post-purge) before being de-energized.
Also, the indoor blower runs for a designated peri-
od (90--240 seconds) as set by switches on furnace
control.