Control Box; Control Transformer; Door Interlock Switch; I Unit Components - Lennox G61MPV Service Manual

I−UNIT COMPONENTS
G61MPV 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.
G61MPV 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 discharge by
putting the furnace, the control and the techni-
cian at the same electrostatic potential. Neutral-
ize electrostatic charge by touching hand and all
tools on an unpainted unit surface, such as the
gas valve or blower deck, before performing any
service procedure.
A−Control Box
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 G61MPV
DOOR INTERLOCK
SWITCH
SURELIGHT®
CONTROL
BOARD
FIGURE 2
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.
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)
G61MPV units are equipped with the Lennox two−stage,
variable speed integrated SureLight® control. The sys-
tem consists of a ignition / blower control (figure 4 with
control terminal designations in tables 1 through 4) and ig-
nitor (figure 12). The control and ignitor work in combina-
tion to ensure furnace ignition and ignitor durability. The
SureLight integrated board controls all major furnace op-
erations. The control features two LED lights, (DS1 and
DS2) for troubleshooting and four LED lights (DS3, DS6,
DS7 and DS8) to show furnace status. The control also
has two accessory terminals rated at (1) one amp each.
See table 5 for status code and table 6 for troubleshooting
diagnostic codes.
CIRCUIT
BREAKER
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 or second stage prove switch is
closed (jumpered). Likewise the control will not begin the
second stage heating cycle if the second stage prove
switch is closed, and will remain in first stage heat. Howev-
TRANSFORMER
er, if the second stage prove switch closes during the first
stage heat pre−purge, the control will allow 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−minute re−set period.
Page 24
CIRCUIT BREAKER CB8
PRESS TO RESET
FIGURE 3
WARNING
SureLight Board 49M59