I Unit Components - Lennox G60UH Service Manual

I−UNIT COMPONENTS
G60UH(X) unit components are shown in figure 1. The gas
valve, combustion air inducer and burners can be ac-
cessed by removing the burner access panel. Electrical
components are in the control box (figure 2) found in the
blower section.
G60UH(X) units are factory equipped with a bottom return air
panel in place. The panel is designed to be field removed as
required for bottom air return. Markings are provided for side
return air and may be cut out in the field.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace's
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis-
charge by putting the furnace, the control and
the technician at the same electrostatic poten-
tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per-
forming any service procedure.
1. Control Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. Transformers on all
models are rated 40VA with a 120V primary and a 24V sec-
ondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in se-
ries with line voltage. When the blower door is removed the
unit will shut down.
CONTROL BOX G60UH(X)
Control Transformer
Circuit Breaker
FIGURE 2
Door Interlock Switch
Two−Stage Integrated
Control Board
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box.
The switch provides overcurrent protection to the trans-
former (T1). The breaker is rated 3A at 32V. If the current
exceeds this limit the breaker will trip and all unit opera-
tion will shutdown. The breaker can be manually reset
by pressing the button on the face. See figure 3.
CIRCUIT BREAKER CB8
PRESS TO RESET
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.
4. Integrated Control Board(A92)
®
SureLihgt Board 18M34
All G60UH units are equipped with the Lennox Two−Stage
Integrated control board. The system consists of a igni-
tion control board (figure 4 with control terminal designa-
tions in tables 3, 4 and 5). and ignitor (figure 7). The board
and ignitor work in combination to ensure furnace ignition
and ignitor durability. The board controls all major furnace
operations. The board features two LED lights, DS1 and
DS2 for troubleshooting. The board also has two accesso-
ry terminals rated at (1) one amp. See table 6 for trouble-
shooting diagnostic codes.
Electronic Ignition
At the beginning of the heat cycle, SureLight control moni-
tors the first stage and second stage combustion air induc-
er prove switch. The control will not begin the heating cycle
if the first stage prove switch is closed (by−passed). Like-
wise the control will not begin the second stage heating
cycle if the second stage prove switch is closed, and will al-
low first stage heat only. However if the second stage prove
switch closes during the first stage pre−purge, the control
will respond to second stage heat. Once the first stage
prove switch is determined to be open, the combustion air
inducer 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−min-
ute 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
Page 12
FIGURE 3
WARNING