LG AR-DR12-05A Installation And Operation Manual page 86

INDIRECT GAS FIRED FURNACES
Furnace Start Up
Modulating Valve Low Fire Setting
Conduct this step when the Commissioning Menu reaches the Low Fire Setting screen.
1. With a manometer installed at the burner manifold test port, press and hold
down button #2 until the LED blinks red. Release the button. Observe the gas
pressure on the manometer.
2. Adjust the Low Fire setting by pushing button #1 to increase the pressure or by
pushing button #2 to decrease the pressure.
3. Save the Low Fire setting by simultaneously holding down buttons #1 and #2
until the LED turns off. If the new setting is not saved within five minutes, the
Modulating Valve will default back to its last saved setting.
Continue through the Commissioning Menu to verify proper furnace operation. If additional furnaces are present, the Commissioning Menu
will step through setting up those furnaces as well. Reference the appropriate section in this IOM for detailed information about each furnace.
Reinstall the cover on the modulating valve, remove the manometer and reinstall the plug in the manifold test port.
High Turndown Electronic Modulation
High turndown furnaces use a split burner manifold with a shutoff and a modulating valve on each manifold section. High and low fire manifold pres-
sure must be checked and properly set on each manifold section.
Furnaces with electronically modulated high turndown control use two combination valves for primary gas control – one valve controls each
manifold section.
They control the high fire gas supply and act as on/off switching devices. The combination valves are normally closed and require 24 VAC to
hold them open.
A modulating valve is located just after each combination valve. The modulating valve is the device that modulates or changes the gas vol-
ume that is being supplied to the furnace manifold. Its function is described in the 4:1 Turndown Electronic Modulation section.
When a manifold section is initiated, the furnace 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 gas to be reduced to as little as 25%
of full flow (4:1 turndown) based on demand.
If less heat is needed, a manifold section is turned off and the remaining manifold section is allowed to modulate based on demand.
Adjustment of the high turndown modulation system follows the same steps as the 4:1 modulation system. The same settings must be per-
formed on each manifold section. Refer to the 4:1 modulation section for proper adjustment of each section of the high turndown modulating
furnace.
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