Other Unit Adjustments; Primary And Secondary Limits; Flame Rollout Switches; Pressure Switches - Lennox G71MPP-36B-070 Installation Instructions Manual

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 (Three)
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,
Back-Up Secondary Limit (090, 110 and 135)
The back-up secondary limit is located on the combustion
air inducer. This switch protects the plastic components
from overheating due to indoor blower motor failure, If
tripped, check for proper blower operation before resetting,
Temperature Rise
After the furnace has been started and supply and return
air temperatures have been allowed to stabilize, check the
temperature rise with the unit operating at 100 percent fir-
ing rate. 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.
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.
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,
Electronic Ignition
The 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 demand
for heat, the Watchguard will break and remake thermostat
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, call the service technician to inspect the unit
for blockages.
10 - Is blower harness connected to ignition control? Fur-
nace will not operate unless harness is connected.
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