Other Unit Adjustments - Lennox G51MP SERIES Installation Instructions Manual

Other Unit Adjustments

Primary and Secondary Limits
The primary limit is located on the heating compartment
vestibule panel. The secondary limits are located in the
blower compartment, attached to the back side of the blow-
er. These limits are factory set and require no adjustment.
Flame Rollout Switches (Two)
These manually reset switches are located on the burner
box. If tripped, check for adequate combustion air before
resetting.
Pressure Switches (Two)
The pressure switches are located in the heating compart-
ment on the combustion air inducer. These switches check
for proper combustion air inducer operation before allow-
ing ignition trial. The switches are factory−set and require
no adjustment.
Temperature Rise
After the furnace has been started and supply and return air
temperatures have been allowed to stabilize, check the
temperature rise. If necessary, adjust the blower speed to
maintain the temperature rise within the range shown on
the unit nameplate. Increase the blower speed to decrease
the temperature. Decrease the blower speed to increase
the temperature rise. Failure to adjust the temperature rise
may cause erratic limit operation.
Fan Control
Heating Mode −− The fan on delay of 45 seconds is not
adjustable. The fan off delay (amount of time that the
blower operates after the heat demand has been satis-
fied) may be adjusted by setting S1 switches 1 and 2 lo-
®
cated on the SureLight control. The unit is shipped with
a factory fan off setting of 90 seconds. The fan off delay
affects comfort and is adjustable to satisfy individual ap-
plications. Adjust the fan off delay to achieve a supply air
temperature between 90° and 110°F at the exact mo-
ment that the blower is de−energized. Longer off delay
settings provide lower return air temperatures; shorter
settings provide higher return air temperatures. See fig-
ure 53.
Cooling Mode −− The cooling mode fan off delay (amount
of time that the blower operates after the cooling demand
has been satisfied) may be adjusted by setting S1 switch
3 located on the SureLight
the cooling fan off delay is 2 seconds. In the on position,
the cooling fan off delay is 45 seconds. See figure 53.
Thermostat Heat Anticipation
Set the heat anticipator setting (if adjustable) according to
the amp draw listed on the wiring diagram that is attached
to the unit.
®
control. In the off position,
Electrical
1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating).
3 − Check amp-draw on the blower motor.
Motor Nameplate__________Actual__________
NOTE − Do not secure the electrical conduit directly to the
air ducts or structure.
Blower Speeds
NOTE − CFM readings are taken external to unit with a dry
evaporator coil and without accessories.
Turn off electrical power to furnace.
Remove blower access panel.
Disconnect existing speed tap at control board speed
terminal.
NOTE − Termination of any unused motor leads must be
insulated.
Refer to blower speed selection chart on unit wiring dia-
gram for desired heating or cooling speed. See blower
performance data beginning on Page 44.
Connect selected speed tap at control board speed
terminal.
Resecure blower access panel.
Turn on electrical power to furnace.
Electronic Ignition
®
The SureLight integrated control has an added feature of
an internal Watchguard control. The feature serves as an
automatic reset device for ignition control lockout caused by
ignition failure. This type of lockout is usually due to low gas
line pressure. After one hour of continuous thermostat de-
mand for heat, the Watchguard will break and remake ther-
mostat demand to the furnace and automatically reset the
control to begin the ignition sequence.
Exhaust and Air Intake Pipe
1 − Check exhaust and air intake connections for tightness
and to make sure there is no blockage.
2 − Are pressure switches closed? Obstructed exhaust
pipe will cause unit to shut off at pressure switches.
Check termination for blockages.
3 − Reset manual flame rollout switches on burner box
cover.
Failure To Operate
If the unit fails to operate, check the following:
1 − Is the thermostat calling for heat?
2 − Are access panels securely in place?
3 − Is the main disconnect switch closed?
4 − Is there a blown fuse?
5 − Is the filter dirty or plugged? Dirty or plugged filters will
cause the limit control to shut the unit off.
6 − Is gas turned on at the meter?
7 − Is the manual main shut-off valve open?
8 − Is the internal manual shut-off valve open?
9 − Is the unit ignition system in lock out? If the unit locks out
again, inspect the unit for blockages.
Page 43