Lennox ML296UHV Series - Page 51

Page 51
Heating
On a call for heat from the room thermostat, the control
board performs a 1 second self check. Upon conrma-
tion that the pressure switch contacts are in an open posi-
tion, the control energizes the combustion blower on high
speed. The control then checks for adequate combustion
air by making sure the low-re pressure switch contacts
are closed.
The igniter energizes and is allowed to warm up for 20
seconds before the gas valve energizes on 1st stage and
burners ignite. 30 seconds after ignition the circulating
blower is energized. 45 seconds after the control conrms
ignition has occurred, the control drops the combustion
blower to low speed.
The circulating blower operates at full 1st stage heat speed
until either the heat call is satised or the thermostat initi-
ates a call for 2nd stage heat. On a call for 2nd stage heat,
the control energizes the circulating air blower on full CFM
2nd stage heat.
If the automatic heat staging option is being used the fur-
nace does not switch to 2nd stage heat in response to a
call from the thermostat but instead operates at 1st stage
heat for the duration of the selected time before automati-
cally switching to 2nd stage heat.
When the call for heat is satised, the gas valve and com-
bustion air blower shut down. The control board shuts o󰀨
the gas valve and runs the combustion blower for an addi-
tional 15 seconds. The circulating air blower continues to
run the selected heat blower o󰀨 delay time. before ramp-
ing down. In the event the unit loses ignition, the control
will attempt to recycle up to ve times before it goes into
a 1 hour lockout.
Lockout may be manually reset by removing power from
the control for more than 1 second or removing the ther-
mostat call for heat for more than 3 seconds.
If during a heating cycle the limit control senses an ab-
normally high temperature and opens, the control board
deenergizes the gas valve and the combustion blower
while the circulating blower ramps up to 2nd stage heat
speed. The circulating blower remains energized until the
limits are closed.
Fan On
When the thermostat is set for continuous fan operation
and there is no demand for heating or cooling, a call for
fan closes the R to G circuit energizing the the circulating
blower. For -55 units the motor runs at 50% of the selected
cooling CFM and for -56 units the motor runs at 38% of the
selected cooling CFM, until switched o󰀨. When the call for
fan is turned o󰀨, the control de-energizes the circulating
blower.
Cooling
The unit is set up at the factory for single stage cooling.
For two stage cooling operation, clip the jumper wire lo-
cated between the Y to Y2 terminals on the integrated ig-
nition/ blower control board. If the active dehumidication
feature is enabled, the circulating blower runs at 70% of
the selected cooling speed as long as there is a call for
dehumidication.
IMPORTANT
The system MUST NOT be in either the passive
OR active dehumidication mode when charging a
cooling system.
Single Stage Cooling
A call for cooling from the thermostat closes the R to Y
circuit on the integrated ignition/blower control board. The
control waits for a 1-second delay before energizing the
circulating blower to 82% of the selected cooling CFM
(passive dehumidication mode). After 7.5 minutes, the
circulating blower automatically ramps up to 100% of the
selected cooling airow. When the call for cooling is satis-
ed, the circulating blower ramps back down to 82% of the
selected cooling airow for 1 minute, then shuts o󰀨.
Two-Stage Cooling
A call for 1st stage cooling from the thermostat closes the
R to Y circuit on the control board. The control waits for a
1- second delay before energizing the circulating blower.
The blower motor runs at 57% of the selected air ow for
the rst 7.5 minutes of the 1st stage cooling demand (pas-
sive dehumidication mode). After 7.5 minutes, the blower
motor runs at 70% of the selected cooling air ow until 1st
stage cooling demand is satised.
A call for 2nd stage cooling from the thermostat closes
the R to Y2 circuit on the control board. The blower motor
ramps up to 100% of the selected cooling air ow. When
the demand for cooling is met, the blower ramps down to
Y1 until satised, then ramps down to 57% for 1 minute,
then turns o󰀨.
Heat Pump
For heat pump operation, clip the jumper wire located bel-
low the O terminal on the integrated ignition/blower control
board. In heat pump mode, a call for heat will result in the
circulating air blower operating at the selected cooling air-
ow after a brief ramp-up period.