MG2S Installation Manual

24
6. The manifold pressure must be set to the appropriate
value for each installation by a qualified installer, service
agency or the gas supplier.
WARNING:
Do not attempt to drill the gas orifices. Use only
factory supplied orifices. Improperly drilled
orifices may cause fire, explosion, carbon
monoxide poisoning, personal injury or death.
a.) Obtain the manifold pressure setting required for
this installation by referring to Table 11 for Propane
or Table 13 or Table 14, (page 36) for Natural
Gas.
b.) Remove the regulator capscrew from the INLET
side of the regulator. See Figure 21.
c.) Slowly turn the adjustment screw inside the regulator
to obtain the appropriate manifold pressure.
NOTE: Turning the screw clockwise increases the
pressure and turning the screw counter-clockwise
decreases the pressure. To prevent backing the
screw all the way out from the valve, turn the screw
slowly.
d.) Replace and tighten the regulator capscrew over
the adjustment screw.
Verifying & Adjusting Temperature Rise
After installation of the furnace, confirm the temperature
rise of the furnace is within the limits specified on the rating
plate. Any temperature rise outside the specified limits
could result in premature failure of the heat exchanger.
For typical duct systems, the temperature rise will fall
within the limits specified on the rating plate with the
blower speed at the factory recommended setting. If the
measured temperature rise is outside the specified limits,
it may be necessary to change the speed of the blower.
NOTE: Lowering the blower speed will increase the
temperature rise and a higher blower speed will decrease
the temperature rise.
The furnace is equipped with a multi-speed motor.
Heating and cooling speed selection is made by moving
the switches on the blower control in the box in front of
the blower.
1. Place thermometers in the return and supply air stream
as close to the furnace as possible.
IMPORTANT: The thermometer on the supply air
side must be shielded from direct radiation from
the heat exchanger to avoid false readings.
2. Consult Table 7, (page 32) and the rating plate for
the proper circulating air flow and temperature rise.
NOTE: This furnace is designed to operate with a maximum
external pressure rise of 0.3 inches of water column. It
is important that the duct system be designed to provide
the correct flow rates and external pressure rise. An
improperly designed duct system can result in nuisance
shutdowns, and comfort or noise issues.
3. Adjust all registers and duct dampers to the desired
position and run the furnace for 10 to 15 minutes before
taking any temperature readings. The temperature rise
is the difference between the supply and return air
temperatures.
NOTE: The settings in Table 6 refer to the small white
switches on the red HEAT / COOL switch socket on the
motor control board. The switches are set by the factory
for good performance in a typical installation. If needed,
the switches can be changed to ON or OFF by sliding
them with a small screwdriver. See Figure 26 (page 33).
Verifying Burner Operation
CAUTION:
The door over the burners may only be open
for inspection purposes only. The door must be
installed during unattended operation.
1. Set the thermostat above room temperature and observe
the ignition sequence. NOTE: The burner flame should
carry over immediately between all burners without
lifting off, curling, or floating. The flames should be
blue, without yellow tips.
Figure 21. Gas Valve
Model VR9205Q1127
Manual
ON / OFF
Switch
HI Input
Adjusting Screw
Lo Input
Adjusting Screw
Inlet Pressure Tap