I-Unit Components - Lennox ML193UH045P36B Unit Information

I-UNIT COMPONENTS

ML193UH unit components are shown in figure 1. The
combustion air inducer, gas valve and burners can be ac­
cessed by removing the burner access panel. The blower
and control box can be accessed by removing the blower
access door.
A-Control Box Components (Figure 2)
Unit transformer (T1) and integrated ignition control (A92)
are located in the control box. In addition, a door interlock
switch (S51) is located in the control box.
ML193UH Control Box
TRANSFORMER
(T1)
DOOR INTERLOCK
SWITCH (S51)
FIGURE 2
1. Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. The transformers on all
models are rated at 40VA with a 120V primary and 24V
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located on
the control box. The switch is wired in series with line volt­
age. When the blower door is removed the unit will shut
down.
3. Integrated Ignition Control 100973 (A92)
CAUTION
Electrostatic discharge can affect elec­
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
INTEGRATED IGNITION
CONTROL
(A92)
Page 7
WARNING
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply re­
place entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
The ignition control system consists of an integrated con­
trol (figure 4) ignitor (figure 10) and flame sensor (figure
10). The integrated control and ignitor work in combination
to ensure furnace ignition and ignitor durability. The inte­
grated control, controls all major furnace operations. The
integrated control also features two LED lights (DS1 red
and DS2 green) for troubleshooting and two accessory ter­
minals rated at (1) one amp. The integrated control also
features a (3) amp fuse for overcurrent protection. Tables 1
and 2 show jack plug terminal designations. See table 3 for
troubleshooting diagnostic codes. The 95 volt ignitor is
made from a high strength, silicon nitride material that pro­
vides long life and trouble free maintenance. The inte­
grated control continuously monitors line voltage and
maintains the ignitor power at a consistent level to provide
proper lighting and maximum ignitor life.
TABLE 1
4-Pin Terminal Designation
PIN #
1 Combustion Air Inducer Line
2 Ignitor Line
3 Combustion Air Inducer Neutral
4 Ignitor Neutral
TABLE 2
12-Pin Terminal Designations
PIN #
1 High Limit Output
2 Not Used
3 24V Line
4 Not Used
5 Rollout Switch Out
6 24V Neutral
7 High Limit Input
8 Ground
9 Gas Valve Common
10 Pressure Switch In
11 Rollout Switch In
12 Gas Valve Out
Electronic Ignition (See Figure 5)
On a call for heat the integrated control monitors the com­
bustion air inducer prove switch. The integrated control will
not begin the heating cycle if the prove switch is closed (by-
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differen­
FUNCTION
FUNCTION