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Start-Up — Indirect Gas-Fired Heating
3. Confirm Gas Flow at Unit:
Open door to unit vestibule housing the gas heater.
Move gas control lever to "OFF" position. Remove
1/8-in. pressure taps from both modulating and on-off
sections of the split heater manifold. Install a barbed
fitting in both 1/8-in. tapped holes for connection to
individual gas manometers.
Note: There is a third 1/8-in. gas pressure tap located
in the pipe connecting the main valve/regulator
and modulating valve. Maximum pressure into
modulating valve is 5-in. The On-Off gas valve
includes a regulator adjustment device that is
located on the top of the valve. Use this device
to regulate valve output to modulating valve as
required.
4. Wait 5 minutes for any gas to clear. If you smell gas,
Step 2
and correct leak. If you don't smell gas or have
corrected any leaks, go to the next step.
5. Main Gas Supply:
Turn manual gas cock "ON" .
6. Pre-purge and Ignition:
a. Open all manual gas valves.
b. Turn power on at the gas heat switch inside the gas
heat vestibule.
c. A call for heat is initiated by the AHU unit control
through a 0-10V analog signal.
d. The heater controller will then go through a system
check to ensure that the high temperature limit and
rollout switches are closed, the air pressure switch
is open, and the modulating valve is positioned
correctly.
e. The control will then enter the pre-purge cycle,
where the inducer will run at the programmed
purge pressure. During this cycle, the control will
look for the air pressure switch to close and open at
the correct settings.
f. Once the system check and pre-purge cycles are
complete, the control will enter the ignition cycle.
The modulating valve and inducer will go to their
"light off" settings.
The DSI ignition module will be energized and the
spark ignitor will activate.
The redundant safety valve will open, allowing gas
flow.
The burners will ignite and the control will receive
a signal from the flame sensor.
The spark ignitor will remain active for the duration
of the ignition cycle, regardless of flame status.
g. If flame is not established during the ignition cycle,
the control will repeat the pre-purge and ignitions
cycles up to three times. After three failed ignition
attempts, the board will enter a 1 hour lockout.
h. Once flame has been established, the control will
enter a warm-up period to ensure flame
20
stabilization and reduce condensation in the heat
exchanger.
i. After the warm-up period, the control will enter the
run cycle. During the run cycle, the burner firing rate
and draft inducer pressure are determined based on
the heat demand received by the control via a 0-10V
analog signal.
Note: If the control is paired with a split manifold,
through
Step h
pertain to the primary burners.
Once the control exits the warm-up period and the
firing rate is dictated by the rooftop control, the
control will ignite the secondary burners and
modulate the primary burners based on the
demand for heat.
j. The run cycle will continue until any of the following
conditions are met.
• The call for heat is terminated.
• Any of the safety devices (high limit, air
pressure, rollout, etc.) are triggered.
• The control reaches it's maximum run time of 6
hours. If this condition is reached, the control
will terminate the run cycle, continue through
the proper sequence of operations, and then
immediately enter the system check and pre-
purge cycles to prepare for re-ignition,
assuming conditions A and B haven't been met.
k. Once the run cycle has terminated, the redundant
safety valve will close, the modulating valve will
return to its set position, and the draft inducer will
ramp up to its "light-off" setting for a 45 second
post-purge cycle.
l. After the conclusion of the post-purge, the control
will enter the "OFF" state. All system outputs are
de-energized but all safety devices are still
monitored.
m. When the building management system
temperature is satisfied and the demand for heat
ends, the gas valve is de-energized immediately
and the combustion blower is energized on high
speed for 30-second post-purge period.
n. If the unit fails to ignite see Troubleshooting
chapter.
Step c
CLCH-SVX014B-EN
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