Modulating Gas Valve - Lennox LGH420 Installation Instructions Manual

TO LEFT HEAT
SECTION
LEFT HEAT SECTION
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 5.
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.
NOTE - BOTH GENERAL PURPOSE BOARD SWITCHES
MUST BE OFF FOR NORMAL UNIT OPERATION. SEE
FIGURE 6.
2- After the unit has operated for 5 minutes, use the Unit
Controller menu path MAIN > SERVICE > TEST >
HEAT > HEAT 2. 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.
4- After the unit has operated for 5 minutes, use the Unit
Controller menu path MAIN > SERVICE > TEST >
HEAT > HEAT 1. The unit will operate at minimum
heating input.
5- Measure the manifold pressure at the gas valves.
Manifold pressures should be:
MODULATING GAS VALVE (MGV)
TO RIGHT
HEAT SECTION
GV4
MODULATING
GAS VALVE
GV1
LEFT HEAT
SECTION GAS
VALVE
MANIFOLD
PRESSURE
PORT
RIGHT HEAT SECTION
MODULATING
FIGURE 5
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 (A55)
DIP SWITCHES IN
OFF POSITION FOR
NORMAL OPERATION
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 8
GV5
GAS VALVE
MANIFOLD
PRESSURE PORT
GV3
RIGHT HEAT
SECTION GAS
VALVE
GP3
(A187)
BOARD
FIGURE 6
MGVs
Modulate
Further
Closed
MGVs
Modulate
Further
Open
GAS
INLET
Heating
Output
Lowers
Heating
Output
Increases