Lennox ML193UHE Series Unit Information page 9

IGNITION CONTROL 103217-03
RED LED
RECALL BUTTON
FIGURE 3
Electronic Ignition
On a call for heat the integrated control monitors the com-
bustion air inducer pressure switch. The control board will
not begin the heating cycle if the pressure switch is closed
(by-passed). Once the pressure switch is determined to
be open, the combustion air inducer is energized. When
the differential in the pressure switch is great enough, the
pressure switch closes and a 15-second pre-purge be-
gins. If the pressure switch is not proven within 2-1/2 min-
utes, the integrated control goes into Watchguard-Pres-
sure Switch mode for a 5-minute re-set period.
After the 15-second pre-purge period, the ignitor warms
up for 20 seconds during which the gas valve opens at
19 seconds for a 4-second trial for ignition. The ignitor re-
mains energized for the first 3 seconds during the 4 second
trial. If ignition is not proved during the 4-second period,
the integrated control will try four more times with an inter
purge and warm-up time between trials of 35 seconds.
After a total of five trials for ignition (including the initial
trial), the integrated control goes into Watchguard-Flame
Failure mode. After a 60-minute reset period, the integrat-
ed control will begin the ignition sequence again.
BLOWER OFF DELAY
Fan Time Control - Ignition Control 103217-03
Heating Fan On Time
The fan on time of 30 seconds is not adjustable.
Heating Fan Off Time
Fan off time (time that the blower operates after the heat
demand has been satisfied) can be adjusted by moving
the jumper to a different setting. The unit is shipped with
a factory fan off setting of 90 seconds. For customized
comfort, monitor the supply air temperature once the heat
demand is satisfied. Note the supply air temperature at
the instant the blower is de-energized.
Adjust the fan-off delay to achieve a supply air tempera-
ture between 90° - 110° at the instant the blower is de-en-
ergized. (Longer delay times allow for lower air tempera-
ture, shorter delay times allow for higher air temperature).
See FIGURE 4.
Cooling Fan On Time
The fan on time is 2 seconds and is not adjustable.
Cooling Fan Off Time
The control has a 45 second fan off delay after cooling
demand has been met. This delay is factory set and not
adjustable.
HEAT FAN OFF TIME IN SECONDS
To adjust fan-off timing, reposition jumper across pins to
60 Second 90 Second
off Time
Page 9
NO JUMPER
achieve desired setting.
120 Second
off Time off Time
FIGURE 4
180 Second
off Time