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 blow-
er 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 (A92)
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 6) and flame sensor (figure 6).
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 IGNITION
CONTROL
(A92)
Page 7
integrated control also features two LED lights (DS1 red
and DS2 green) for troubleshooting and two accessory
terminals 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 mini−nitride ignitor
is made from a non−porous, high strength proprietary ce-
ramic material that provides long life and trouble free
maintenance. The integrated control continuously moni-
tors line voltage and maintains the ignitor power at a con-
sistent level to provide proper lighting and maximum igni-
tor 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-
tial in the prove switch is great enough, the prove switch
closes and a 15−second pre−purge begins. If the prove
switch is not proven within 2−1/2 minutes, the integrated
control goes into Watchguard−Pressure Switch mode for a
5−minute re−set period.
FUNCTION
FUNCTION