Other Unit Adjustments; Sequence Of Operation - Lennox EL280UH070P24A Installation Instructions Manual

Other Unit Adjustments

Primary and Secondary Limits
The primary limit is located on the heating compartment
vestibule panel. The secondary limits (if equipped) are lo-
cated in the blower compartment, attached to the back
side of the blower. These auto reset limits are factory-set
and require no adjustment.
Flame Rollout Switches
This manually reset switches are located on the baffle
plate in the burner assembly.
Pressure Switch
The pressure switch is located in the heating compartment
adjacent to the combustion air inducer. The switch checks
for proper combustion air inducer operation before allow-
ing ignition trial. The switch is factory-set and requires no
adjustment.
Temperature Rise
After the furnace has been started, and supply and return
air temperatures have been allowed to stabilize, check the
temperature rise. If necessary, adjust the blower speed
to maintain the temperature rise within the range shown
on the unit nameplate. Increase the blower speed to de-
crease the temperature. Decrease the blower speed to
increase the temperature rise. Failure to adjust the tem-
perature rise may cause erratic limit operation.
Fan Control
The fan-on time of 30 seconds is not adjustable. The heat
fan-off delay (amount of time that the blower operates af-
ter the heat demand has been satisfied) may be adjusted
by changing DIP switches 3 and 4. See figure 32 and table
8. The unit is shipped with a factory fan-off delay setting
of 90 seconds. The fan-off delay affects comfort and is
adjustable to satisfy individual applications. Adjust the fan-
off delay to achieve a supply air temperature between 90°
and 110°F at the moment that the blower is de-energized.
Longer off delay settings provide lower return air tempera-
tures; shorter settings provide higher return air tempera-
tures.
NOTE - Do not secure the electrical conduit directly to the
air ducts or structure.
HEAT FAN OFF TIME IN SECONDS
60sec.
1 2 3 4 5
120sec.
1 2 3 4 5
To adjust fan-off timing, flip dip switch to desired setting.
FIGURE 32
90sec.
1 2 3 4 5
180sec.
1 2 3 4 5
Electrical
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%.
3 - Check amp-draw on the blower motor with inner
blower panel in place.
Unit Nameplate__________Actual__________
Blower Speeds
Follow the steps below to change the blower speeds.
1 - Turn off electrical power to furnace.
2 - Remove blower access panel.
3 - Disconnect existing speed tap at integrated control
speed terminal.
NOTE - Termination of any unused motor leads must be
insulated.
4 - Place unused blower speed tap on integrated
control "PARK" terminal or insulate.
5 - Refer to blower speed selection chart on unit wiring
diagram for desired heating or cooling speed. See
Blower performance data beginning on the next
page.
6 - Connect selected speed tap at integrated control
speed terminal.
7 - Resecure blower access panel.
8 - Turn on electrical power to furnace.
9 - Recheck temperature rise.
Electronic Ignition
The integrated control has an added feature of an internal
Watchguard control. The feature serves as an automat-
ic reset device for integrated control lockout caused by
ignition failure. This type of lockout is usually due to low
gas line pressure. After one hour of continuous thermostat
demand for heat, the Watchguard will break and remake
thermostat demand to the furnace and automatically reset
the integrated control to begin the ignition sequence.
Heating Sequence of Operation
When there is a call for heat, the integrated control runs a
self check. The control checks for S10 primary limit, S21
secondary limit (s) and S47 rollout switch normally closed
contacts. The control also checks for S102 high heat and
S128 low heat prove switch normally open contacts. Once
self check is complete and all safety switches are opera-
tional, heat call can continue.
Two-Stage Thermostat, Two Stage Heat. Dip Switch
set at "TWO".
1 - SureLight® control energizes combustion air inducer
B6 on low heat speed. Combustion air inducer runs
until S128 low heat prove switch contacts close
(switch must close within 2 1/2 minutes or control
goes into Watchguard Pressure Switch mode.
High heat prove switch S102 may also close). A 15
second pre-purge follows once S128 closes.
Page 32