Integrated Control Board(A92) - Lennox G60UHV Service Manual

WARNING
Shock hazard.
Disconnect power before servicing. Integrated
Control Board is not field repairable. If control is
inoperable, simply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.

5. Integrated Control Board(A92)

Board 100870
Beginning with G60UHV−7, units are equipped with the
Lennox two−stage, variable speed integrated SureLight
control board. The system consists of a ignition / blower
control board (figures 5 and 6) with control pin designa-
tions in tables 12, 13 and 14 and ignitor (figure 13). The
board and ignitor work in combination to ensure furnace
ignition and ignitor durability. The SureLight integrated
board controls all major furnace operations. The board
features a red LED light, for furnace status and trouble-
shooting. The LED flashes in X" + Y" codes. For example
using table 15 under PRESSURE SWITCH CODES", if
the red LED flashes 2 times, then off for 2 seconds then
flashes 3 times, the low pressure switch is failed open.
Two green LEDs show indoor blower status and CFM. See
Page 21 for more detail. The board also has two 120 volt
accessory terminals rated at (1) one amp each. In addition
there is a 24 volt accessory terminal located on TB1.
Electronic Ignition
At the beginning of the heat cycle the SureLight control
monitors the first stage and second stage combustion air
inducer prove switch. The control will not begin the heating
cycle if the first stage prove switch is closed (by−passed).
Likewise the control will not begin the second stage heating
cycle if the second stage prove switch is closed, and will re-
main in first stage heat. However, if the second stage prove
switch closes during the first stage heat pre−purge, the con-
trol will allow second stage heat. Once the first stage prove
switch is determined to be open, the combustion air induc-
er is energized on low (first stage) heat speed. When the
differential in the prove switch is great enough, the prove
switch closes and a 15−second pre−purge begins. If the
switch is not proven within 2−1/2 minutes, the control goes
into Watchguard−Pressure Switch mode for a 5−minute re−
set period.
After the 15−second pre−purge period, the SureLight ignitor
warms up for 20 seconds after which the gas valve opens
for a 4−second trial for ignition. The ignitor energizes during
the trial until flame is sensed. If ignition is not proved during
the 4−second period, the control will try four more times with
an inter purge and warm−up time between trials of 35 sec-
onds. After a total of five trials for ignition (including the ini-
tial trial), the control goes into Watchguard−Flame Failure
mode. After a 60−minute reset period, the control will begin
the ignition sequence again.
NOTE − Board 100870 provides a regulated 95 volts to
to the ignitor.
Two Stage Operation / Thermostat Selection Jumper
The control can be utilized in two modes: SINGLE−STAGE
thermostat or TWO−STAGE thermostat. The thermostat
selection is made using a dip switch (figure 4) and must be
positioned for the particular application. The dip switch is
factory set on TWO" for use with a two−stage thermostat
with two stage heat. Re−position dip switch to SINGLE" for
use with a single stage thermostat with two stage heat.
While in the single−stage thermostat mode (single dip
switch setting), the burners will always fire on first−stage
heat. The combustion air inducer will operate on low speed
and indoor blower will operate on low heat speed. After a
factory default 10 minute recognition period, the unit will
switch to second stage heat. While in the two−stage ther-
mostat mode (two dip switch setting) the burners will fire on
first−stage heat. The combustion air inducer will operate on
low speed and indoor blower will operate on low heat
speed. The unit will switch to second−stage heat on call
from the indoor thermostat. If there is a simultaneous call
for first and second stage heat, the unit will fire an first stage
heat and switch to second stage heat after 30 seconds of
operation. See Sequence of Operation flow charts in the
back of this manual for more detail.
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