25
c. Set the On-Off Switch to “OFF.”
d. Honeywell - turn gas control knob clockwise
to “OFF” Robertshaw - Push the gas control
lever to “OFF.”
e. For oil, shut off all valves.
f. Replace the furnace door.
THE FURNACE CONTROLS AND FUNC-
TIONS
1. On-Off Switch - This switch turns electrical
power to the furnace on and off. The switch
must be set in the “On” position for the furnace
to operate. For M1G* models, in warm weather
there is a possibility of the blower coming on
periodically or operating continuously due to a
heat buildup within the furnace by a combina-
tion of warm weather and heat from the pilot.
This is normal operation as long as there is
power to the furnace and the On-Off switch
is at the “ON” position. If blower operation is
not desired, the On-Off switch may be set in
the “OFF” position to cut the electrical power
to the furnace.
2. Limit Control - This furnace is protected by
two high temperature safety limit switches.
The auxiliary (upper) limit switch and the high
temperature (lower) limit switch are automatic
reset types. If either limit trips, the burner will
shut off. If either limit switch trips off again
soon after resetting, set the furnace On-Off
switch to the “OFF” position and call your
authorized serviceman.
3. Gas Valve - The gas valves for the gas furnaces
are a 100% shut-off type and will fail safe if
for some reason the gas is turned off. The
valve is a “step-open” type for M1G*-models
and “slow-open” for M1M*- and M1B*-models
which means it opens to a “low-fi re” position,
and after a few seconds, “steps-open” to “high-
fi r e . ”
4. Roll Out Switch - (M1G* - 056 & 070) The
furnace is protected by a manual reset safety
switch located on the bottom left hand side of
the combustion pipe.
5. Oil Burner Primary Control - The primary
control for oil gun furnaces starts the burner,
monitors a safe operating cycle, and shuts
the burner off at the end of a heating cycle.
The control uses a light sensing transducer to
determine if fuel ignition has been successfully
attained. If ignition is not attained by the end
of the safety ignition timing period, the control
shuts the burner off and enters “lock-out.”
6. a. Summer Cooling - (H Series): Your furnace
is equipped to operate the circulating fan only.
Turn the Fan On-Auto switch to the “ON” posi-
tion during warm weather. The blower will now
operate to circulate air in your home through
the duct system.
b. Summer Cooling - (A, B, C, & D Series):
Your furnace is A/C ready, equipped with A/C
relay and transformer. The unit is equipped to
use a 4-wire thermostat. When using a 5-wire
thermostat, RC and RH should be jumped
(see instructions included with thermostat).
17. SERVICE GUIDE
BURNER ADJUSTMENTS
Burner settings and adjustments are made
at the factory. However, these settings may
change during shipping, handling, and instal-
lation. Therefore the following items should be
checked and readjusted if necessary.
Atmospheric Gas with Standing Pilot and Direct
Ignition Furnaces, Including Gas Gun.
a. Gas Pressure
The gas pressure can be checked with a
manometer at the pressure tap located on the
side of the gas valve. The gas valve pressure
regulator can be adjusted by removing the
regulator selector stack and turning the slotted
insert located directly under the selector stack.
The regulator selector stack must be secured
in place before each pressure reading is taken.
Natural gas manifold pressure should be 3.5”
W.C. and L.P. gas manifold pressure should
be 10” W.C. Replace the gas pressure tap
plug on the gas valve.
b. Pilot Flame (Standing Pilot Only)
The pilot fl ame can be adjusted by turning the
pilot adjustment screw, located on top of the
gas valve (See Figure 29). The pilot fl ame
height should be between 3/4” and 1.” The
fl ame tip should be visible just above the pilot
bracket when viewed through the observation
door. The same pilot orifi ce is used with both
natural and L.P. gas.
Table 9. Factory Combustion Air Settings
Model Nat. Gas LP Gas Oil
66,000 3.5 3.5 3
86,000 5.3 6 5
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