4.
The gas valve opens for a trial
for ignition.
5.
The hot surface igniter lights the
gas burners and stays ener-
gized for the first 8 seconds
after the gas valve opens.
OR
The spark igniter lights the
.,.
gas and continues to spark
for seven (7) seconds or until
the flame sensor detects flame.
6.
The remote flame sensor must
note flame ignition for one
second using the process of
flame rectification. If flame is
not sensed, the system goes
through another ignition
sequence. It does this up to
four times.
7.
The main blower starts
20 seconds after flame is
sensed.
8.
When the thermostat cycle
ends, the gas valve closes,
the burners go out, the induced
draft fan runs for a five second
post-purge, and the negative
pressure switch(es) open.
9.
The main blower continues until
timed off by the setting on the
integrated furnace control board.
Sequence if the system doesn't light
or doesn't sense flame:
1. On a call for heat the control
runs the inducer for 30 seconds
to prepurge.
2. After the 30 second prepurge,
the hot surface igniter heats for
30 to 34 seconds. The inducer
continues to run.
3. After igniter warm up, the gas
valve opens for a 9 second
trial for ignition. The inducer
continues and the igniter stays
energized.
4. If flame is not sensed during the
ninth second after the gas valve
opens, the gas valve closes, the
igniter de-energizes, both the
inducer and main blower
operate for 180 seconds.•
This procedure attempts to cool
an open heat assisted limit
(HALC) before locking out. The
procedure is called "self-
healing."
5. The igniter heats for 30 to 34
seconds. After igniter warm up,
the gas valve opens for 9
seconds. If no flame is sensed, it
closes the gas valve, the igniter
de-energizes, the inducer runs
for 30 seconds more before
the next ignition trial.
6.
It repeats this process up to
three times. At the end of the
last try, the inducer stops. The
system is in "soft" lock out.
7. To reset the lock out, make
and break power either at the
thermostat or at the unit
disconnect switch. It then goes
through another set of trials for
ignition.
• Now control board instructions are
modified to allow two attempts at
ignition before running the blowers
for 180 seconds, or "self-healing."
SETTING GAS PRESSURE
The maximum inlet gas supply
pressure to the furnace should be
10.5" w.c. natural gas, or 13" w.c.
LP gas. The minimum supply gas
pressure to the gas valve should be
5" w.c. natural gas, or 11" w.c. LP
gas. A properly calibrated U-Tube
manometer is required for accurate
gas pressure measurements .
Supply Gas Pressure Measure-
ment. A line pressure tap is on the
input side of the gas valve.
1. With gas shut off to the furnace
at the manual gas valve outside
the unit, remove the input
pressure tap plug.
2.
Connect a U-Tube manometer
to the pressure tap.
3.
Turn on the gas supply and
operate the furnace with all
other gas fired units on the
same gas line as the furnace.
4.
Note the line gas pressure.
A. 5" - 10.5" w.c. for
natural gas.
B.
11" - 13" w.c. for LP gas.
FIGURE 65
HOSE CONNECTION TO LINE PRESSURE TAP
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59
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