Furnace - Greenheck IGX Installation, Operation And Maintenance Manual

Electronic Modulation Temperature Controls
A Discharge Temperature Dial is used for temperature control for electronic modulation. The temperature dial will
be located in the furnace control center. If a remote panel has been ordered, the Discharge Temperature Dial will
be located on the panel. The Electronic Modulation (100 - 400 MBH) will modulate from 50% to 100% of furnace
input.
High and Low Fire Settings for Electronic Modulation
Check the high and low gas pressures on initial start up per instructions below. These settings are pre-set at the
factory, but can be adjusted in the field if necessary. Set the high fire first and the low fire second. The low fire
must always be checked if the high fire is changed.
Modulating Valve
Low fire adjustment
A
1. Set the unit to high fire by placing a jumper
between terminals 7 and 8 on the Maxitrol amplifier.
2. Measure the burner manifold pressure for each
furnace at the pressure test port (see Figure 7)
using a high quality manometer that can measure
low gas pressures. The pressure at high fire should
be 3.5 in. wc for natural gas and 10.0 in. wc for LP
Gas. To change the pressure, adjust the high fire
screw (under cap screw) on the combination gas
valve. Clockwise rotation will decrease the gas
pressure and counter clockwise rotation will
increase gas pressure.
3. To get the unit to low fire: Remove the wire from
terminal 3 on the amplifier and isolate it from
touching anything. Set the discharge temperature
selector to the highest setting. If there is a room
B
27
Combination Gas Valve
High fire adjustment
Figure 10: Electronic Modulation Valves
override thermostat, turn the dial to the highest
setting.
4. Measure the manifold pressure on low fire, it should
be 0.88 in. wc for natural gas and 2.5 in. wc for LP
gas.
5. To adjust the low fire, remove the by pass cap (A)
and turn screw (B) as shown in diagram. Adjust the
screw indicated in Figure 10 on the modulating
valve. Clockwise rotation will decrease gas the
pressure and counter clockwise rotation will
increase gas pressure.
6. Reconnect wire to terminal 3.
7. Remove jumper and place all wires back to where
they were and plug the manifold pressure port.