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4-- Ram Control (A3)
Early Model G24M Units
The furnace control combines burner ignition func-
tions with blower control functions.
Early model G24M units utilize a furnace control
manufactured by RAM Electronics Corporation. The
RAM board is a printed circuit board which controls
the blower, gas valve, combustion air blower and igni-
tion spark. It also monitors the flame, limit and gas valve
operation. The control has a non--adjustable, factory
preset on fan timing (45 seconds). Fan off timings
are adjustable. The board utilizes both 120 and 24VAC.
See figure 9. The board is also equipped with a diagnos-
tic LED for use when troubleshooting the unit.
When the furnace is idle (blower off and no heating or
cooling demand), the diagnostic LED flashes at a slow
steady rate. On a call for heat, the diagnostic LED be-
gins flashing at a fast rate and the combustion air
blower is energized. The LED flashes different codes to
indicate problem conditions. The diagnostic LED lights
red (not flashing) to indicate control board failure. Table
7 shows how to interpret the other LED modes.
Pre-Purge
On a call for heat, the combustion air blower begins
operating. If the combustion air prove switch closes,
the combustion air blower continues to operate for 45
seconds (pre-purge) before allowing ignition. Pre-
purge allows the heat exchanger to be cleared of com-
bustion products and to introduce fresh air for com-
bustion. If the combustion air prove switch does not
close, the combustion air blower continues to run in-
definitely (until the prove switch closes).
Post-Purge
After a demand, the combustion air blower continues
to operate for 5 seconds (post-purge) before stopping.
Post-purge allows the heat exchanger to be cleared of
combustion products.
Ignition Control
The ignition control is a direct spark ignition control
module integral to the furnace control. See figure 9.
When there is a call for heat, the control delays ignition
until combustion air blower operation has been proved
and pre-purge period has elapsed. It then opens the gas
valve and generates a spark to ignite the burners. Trial
for ignition lasts for 7 seconds. At the same time, the
control begins monitoring the flame sensor. If the flame
current is too weak (less than 1 microamp) or if the
burners do not ignite (within the 7 second ignition trial),
the control will shut off the spark ignitor and the com-
bustion air blower and de-energize the gas valve.
Flame current should be between 1 and 5 microamps to
keep the gas valve open. See figure 21.
The control will attempt to ignite the burners up to two
more times. Each time the control restarts the ignition
sequence, it begins with a 45 second pre-purge. If flame
is not sensed after the third trial, the control locks out.
Lockout means that the control shuts off the gas valve,
spark and combustion air blower for 60 minutes. At the
end of 60 minutes the control completely resets and
will attempt ignition up to three times. The control can
be manually reset before the end of 60 minutes by mo-
mentarily turning off power to the unit.
DANGER
Shock hazard.
Spark related components contain high voltage.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply re-
place entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.