Start-Up - Furnaces (All Units) - LG GEN2 Series Installation And Operation Manual

Start-Up - Furnaces (all units)

IMPORTANT
For the unit to function properly, ALL gas valves must
have their high fire and low fire settings adjusted for
field conditions.
IMPORTANT
Confirm the discharge air sensor is installed at least
three duct diameters downstream of the furnace.
IMPORTANT
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 (see image).
Test Port
Typical Single Stage Gas Valve
Verify the unit turndown ratio as shown on
page 2 of this manual. Consult the specific
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.
With 4:1 Turndown Electronic
Modulation
ON / OFF
Gas Control Knob
Test Port
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.
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 constantly 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 controller. The controller sends
a 0-10 VDC analog signal to the modulating 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.
Furnace
Controller
EXA Valve
Single Section
Burner Manifold
Discharge Temperature
Sensor
Ignition
Controller
Single Stage
Valve