Furnace Start Up - LG AR-DR12-05A Installation And Operation Manual

INDIRECT GAS FIRED FURNACES

Furnace Start Up

For the unit to function properly, ALL gas valves must have their high fire and low fire settings adjusted for field conditions.
Confirm the discharge air sensor is installed at least three duct diameters downstream of the furnace.
Multi-furnace units may use a combination of the available turndown options. Each furnace must be set-up per the specific
instructions for its control type. For additional information, see Gas-Fired Burner Turndown in this manual.
After the gas piping has been installed and leak tested, verify that all field-installed components such as an air temperature sensor have
been installed. Verify that ON/ OFF gas control knob on each stage-type gas valve is turned to the "ON" position.
Verify the unit turndown ratio as calculated in "Burner Con-
Figure 43: Typical Single Stage Gas Valve
trol Turndown" on page 66 this manual. Consult the specif- ic
start-up instructions as shown on the following pages to accomplish the
following steps.
Set Airflow
Airflow adjustment is done at the time of unit start-up. Refer to the
unit-specific Installation, Operating and Maintenance manual (IOM) for
instructions.
4:1 Turndown Electronic Modulation
Furnaces with electronically modulated 4:1 turndown use a combination
valve for primary gas control. It controls the high fire gas supply and acts
as an on/off switching device. The combination valve is normally closed. It
requires 24 VAC to hold it open.
Figure 44: 4:1 Turndown Electronic Modulation
The modulating valve is located just after the combination valve. The
modulating valve is the device that modulates or changes the gas
volume that is being supplied to the furnace manifold. It has a built-in
digital controller that will accept user settings for High Fire and Low
Fire. During normal use, the amount of combustion gas will vary con-
stantly to regulate the heat output
from the furnace. The modulation is controlled by the microprocessor
controller through the pCOe expansion board or by the furnace con-
troller. The controller sends a 0-10 VDC analog signal to the modulat-
ing valve
that causes the valve to send more or less gas to the furnace. The
valve also requires a 24 VAC power supply to operate.
When a call for heat is provided to the furnace controller or the pCOe
expansion board, the controller will first provide a 10 VDC signal to
the modulating valve so that it will always start in a high fire condition.
After ignition, the controller will change its output signal, causing the
volume of combustion gas to be reduced to as little as 25% of full flow
(4:1 turndown) based on demand.
Both of these valves require adjustment at the time of unit start-up.
Before making furnace adjustments, enter the Commissioning Menu
on the unit or Furnace Controller. The Commissioning Menu is located
under Service > Overrides > Control Loops. Reference the controller
IOM for more information about navigating through the controller
menus. The Commissioning Menu offers a step by step guide to
setting up the furnace. Follow the instructions on the screen. The
following sections of this IOM offer detailed information about setting
the gas pressures.
Due to our policy of continuous product innovation, some specifications may change without notification.
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