Lennox ML296UH045XV36B, Руководство пользователя

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Page 51
On a call for heat from the room thermostat, the control
board performs a 1 second self check. Upon confirmation
that the pressure switch contacts are in an open position,
the control energizes the combustion blower on high
speed. The control then checks for adequate combustion
air by making sure the low-fire pressure switch contacts are
closed.
The igniter energizes and is allowed to warm up for 20 sec­
onds before the gas valve energizes on 1st stage and burn­
ers ignite. 45 seconds after the control confirms ignition
has occurred, the control drops the combustion blower to
low speed.
The circulating blower ramps up to 50% of 1st stage heat
speed and operates at that speed for one minute (including
ramp up time), then at 75% of 1st stage heat speed for an
additional minute. After that, the circulating blower oper­
ates at full 1st stage heat speed until either the heat call is
satisfied or the thermostat initiates a call for 2nd stage heat.
On a call for 2nd stage heat, the control energizes the circu­
lating 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 automatically
switching to 2nd stage heat.
When the call for heat is satisfied, the gas valve and com­
bustion air blower shut down. The control board shuts off
the gas valve and runs the combustion blower for an addi­
tional 15 seconds. The circulating air blower continues to
run for 2 minutes at 82% of the selected heating speed (low
fire or high fire) before ramping down.
In the event the unit loses ignition, the control will attempt to
recycle up to five 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 thermo­
stat call for heat for more than 3 seconds.
If during a heating cycle the limit control senses an abnor­
mally high temperature and opens, the control board de-
energizes 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 and the circulating blower motor
runs at50% of the selected cooling CFM until switched off.
When the call for fan is turned off, 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 located
between the Y to Y2 terminals on the integrated ignition/
blower control board. If the active dehumidification feature
is enabled, the circulating blower runs at 70% of the se­
lected cooling speed as long as there is a call for dehumidi­
fication.
WARNING
The system must not be in either the passive or ac­
tive dehumidification mode when charging a cooling
system.
Single Stage Cooling
A call for cooling from the thermostat closes the R to Y cir­
cuit on the integrated ignition/blower control board. The
control waits for a 1-second delay before energizing the cir­
culating blower to 82% of the selected cooling CFM (pas­
sive dehumidification mode). After 7.5 minutes, the circu­
lating blower automatically ramps up to 100% of the se­
lected cooling airflow. When the call for cooling is satisfied,
the circulating blower ramps back down to 82% of the se­
lected cooling airflow for 1 minute, then shuts off.
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 flow for the first
7.5 minutes of the 1st stage cooling demand (passive de­
humidification mode). After 7.5 minutes, the blower motor
runs at 70% of the selected cooling air flow until 1st stage
cooling demand is satisfied.
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 flow. When the
demand for cooling is met, the blower ramps down to Y1
until satisfied, then ramps down to 57% for 1 minute, then
turns off.
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
flow after a brief ramp-up period.