52
2. Connect a manometer to the pressure tap.
3. Turn on the gas supply and operate the furnace at
100% and all other gas-fired units on the same gas
line as the furnace.
4. Note or adjust the supply-line pressure to give:
A. 5” - 10.5” w.c. for natural gas.
B. 11” - 13” w.c. for LP gas.
If your gas supply does not fall within these ranges,
contact your gas supplier to correct.
5. Shut off the gas at the manual gas valve and remove
the manometer.
6. Replace the supply-line pressure tap plug before turn -
ing on the gas.
7. Check unit for leaks using an approved leak detector.
Do NOT
use a flame of any kind.
OUTLET/MANIFOLD GAS PRESSURE
MEASUREMENT/ADJUSTMENT
Rate adjustment is a combination of selecting the correct
orifices based on heating value and altitude
The outlet/manifold pressure on this modulation furnace is
capa ble of being adjusted at the maximum firing rate and
at the minimum firing rate using the same adjustment
wheel shown in Figure 41. Note: Do not attempt to ad-
just the outlet/manifold pressure at intermediate inputs.
ADJUST MANIFOLD PRESSURE AT
MAXIMUM FIRING RATE
NOTE: HIGH FIRE MUST BE ADJUSTED BEFORE
LOW FIRE
1. With the gas to the unit shut off at the manual gas
valve, remove the outlet/manifold pressure tap plug in
the gas valve. See Figure 39.
2. Install field supplied pressure tap to the outlet/manifold
tap in place of the plug. Connect the positive pressure
hose from a manometer to the pressure tap.
3. Set dip SW10 to the OFF position and dipswitch
SW11 to the ON position (this will force unit to operate
at Maximum Firing Rate only)
4. Remove all thermostat connections to the IFC and
jumper R to W1.
5. Turn gas manual shutoff valve to ON position.
6. Turn on furnace power supply.
7. After ignition, allow furnace to operate and complete
the pressure switch calibration before checking maxi -
mum firing rate outlet/manifold pressure.
Note: The manifold gas pressure to be:
3.5” w.c. (±.3) for natural gas.
10.0” w.c. (±.5) for LP gas.
8. To adjust the outlet/manifold pressure, insert a small
slotted screwdriver into the opening at the top of the
valve (see Figure 41).
FURNACE ADJUSTMENTS
Furnace Adjustments
FIGURE 41
SERVO CONTROLLED GAS VALVE PRESSURE ADJUSTMENT
N
OTE: The adjust-
ment wheel will not
s
top rotating when
it hits the maximum
o
r minimum posi-
tion. Instead, it will
continue to rotate to
t
he opposite adjust-
ment. Use the let-
t
ers on the wheel
a
s a guide.
FIGURE 39
OUTLET / MANIFOLD TAP
ST-A1194-88-00
ST-A1194-88-00
ST-A1194-89-00
SUPPLY PRESSURE TAP
OFF/ON SWITCH
LP JUMPER WELL
(INSERT JUMPER HERE)
ADJUSTMENT WELL
ST-A1194-89-00
FIGURE 40
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