Other Unit Adjustments - Lennox G61MPV?36B?045 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 or Four)
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, 091, 110, 111 & 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. 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 re-
set device for ignition control lockout caused by ignition fail-
ure. This type of lockout is usually due to low gas line pres-
sure. After one hour of continuous thermostat demand for
heat, the Watchguard will break and remake thermostat de-
mand 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.
Heating Sequence of Operation
NOTE − The thermostat selection DIP switchon the control
board is factory−set in the TWO−STAGE" position.
Applications Using a Two−Stage Thermostat
A − Heating Sequence −− Control Board Thermostat
Selection DIP switch in Two−Stage" Position (Factory
Setting)
1 − On a call for heat, thermostat first−stage contacts close
sending a signal to the integrated control. The inte-
grated control runs a self-diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts.The combustion air inducer is ener-
gized at low speed and the humidifier terminal is ener-
gized.
2 − Once the control receives a signal that the low−fire
pressure switch has closed, the combustion air induc-
er begins a 15−second pre−purge in low speed.
3 − After the pre−purge is complete, a 20−second initial ig-
nitor warm−up period begins. The combustion air in-
ducer continues to operate at low speed.
4 − After the 20−second warm−up period has ended, the gas
valve is energized on low fire (first stage) and ignition oc-
curs. At the same time, the control module sends a sig-
nal to begin an indoor blower 45−second ON−delay.
When the delay ends, the indoor blower motor is ener-
gized on the low fire heating speed and the 24V hu-
midifier terminal is energized. The furnace will contin-
ue this operation as long as the thermostat has a
first−stage heating demand.
5 − If second−stage heat is required, the thermostat sec-
ond−stage heat contacts close and send a signal to the
integrated control. The integrated control initiates a
30−second second−stage recognition delay.
6 − At the end of the recognition delay, the integrated con-
trol energizes the combustion air inducer at high
speed. The control also checks the high−fire (second
stage) pressure switch to make sure it is closed. Once
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