Page 7
FIGURE 7
MODULATING GAS VALVE (MGV)
GV1
LEFT HEAT
SECTION GAS
VALVE
GV3
RIGHT HEAT
SECTION GAS
VALVE
GV5
RIGHT HEAT SECTION
MODULATING
GAS VALVE
GV4
LEFT HEAT SECTION
MODULATING
GAS VALVE
GAS
INLET
TO LEFT HEAT
SECTION
TO RIGHT
HEAT SECTION
MANIFOLD
PRESSURE
PORT
MANIFOLD
PRESSURE PORT
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 7.
Operation
The IMC 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, turn the
OPT1 and OPT2 switches ON. See figure 8. 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− Turn the OPT2 switch OFF. 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.
FIGURE 8
TURN UNIT OPT1 SWITCH
ON FOR MINIMUM MGV
HEATING OUTPUT
INITIATE MAXIMUM AND MINIMUM MGV
MODE
UNIT TEST
RECALL
ECTO
TEMP
OPT2
SHIFT
IMC BOARD
UNIT
HP
GAS
OPT1
1PH
TURN UNIT OPT1 AND
MODE OPT2 SWITCHES
ON FOR MAXIMUM MGV
HEATING OUTPUT
6− Turn OPT1 switch OFF.
NOTE − BOTH OPT1 AND OPT2 SWITCHES MUST BE
OFF FOR NORMAL UNIT OPERATION.
IMC Output
The IMC 0−10VDC output to the MGVs increases to
modulate valves further closed during a reduced heating
demand. The IMC 0−10VDC output to the MGVs
decreases to modulate valves further open during a
higher heating demand.
Heating
Demand
Reduces
IMC Output
To MGVs
Increases
MGVs
Modulate
Further
Closed
Heating
Output
Lowers
Heating
Demand
Increases
IMC Output
To MGVs
Reduces
MGVs
Modulate
Further
Open
Heating
Output
Increases
