Modulating Gas Valves - Lennox LGH480 Installation Instructions Manual

TO LEFT HEAT
SECTION
LEFT HEAT SECTION
MODULATING
GAS VALVE
Optional Modulating Gas Valve (MGV)
Units equipped with optional modulating gas valves (MGV)
contain two modulating gas valves in addition to two
standard gas valves. See figure 50.
Operation
The Unit Controller will control modulating gas valves to
maintain 110°F (default) discharge air during the heating
cycle. The left heat section will operate when 25-50% of
nameplate heat is needed. Both heat sections will operate
when 50-100% of the nameplate heat is needed.
The normally open MGV will allow full heating capacity
should the MGV fail.
Start-Up
1- Operate the unit in heating mode according to the
Heating Start-Up section in this manual.
2- After the unit has operated for 5 minutes, use the Unit
Controller Service - Test menu to run high capacity. The
unit will operate at maximum heating input.
3- Measure the manifold pressure at the gas valves.
Manifold pressures should be:
GV1 & GV3:
Natural - 4.0"w.c. LP - 10.8"w.c.
GV4 & GV5:
Natural - 3.7"w.c. LP - 10.5"w.c.
MODULATING GAS VALVE (MGV)
TO RIGHT
HEAT SECTION
GV4
GV1
LEFT HEAT
SECTION GAS
VALVE
MANIFOLD
PRESSURE
PORT
FIGURE 50
GV5
RIGHT HEAT SECTION
MODULATING
GAS VALVE
4- Use the options in the Unit Controller Service Test
menu to run low capacity. The unit will operate at
minimum heating input.
5-Measure the manifold pressure at the gas valves.
Manifold pressures should be:
GV1 & GV3:
Natural - 4.0"w.c. LP - 10.8"w.c.
GV4 & GV5:
Natural - 0.9"w.c. LP - 2.6"w.c.
Unit Controller Output
The Unit Controller 0-10VDC output to the MGVs increases
to modulate valves further closed during a reduced heating
demand. The Unit Controller 0-10VDC output to the MGVs
decreases to modulate valves further open during a higher
heating demand.
Heating
Unit Control­
Demand
ler Output
Reduces
To MGVs
Increases
Heating
Unit Control­
Demand
ler Output
Increases
To MGVs
Reduces
Page 56
MANIFOLD
PRESSURE PORT
GV3
RIGHT HEAT
SECTION GAS
VALVE
GAS
INLET
MGVs
Modulate
Further
Closed
MGVs
Modulate
Further
Open
LGH/LCH420, 480, 540, 600
Heating
Output
Lowers
Heating
Output
Increases