Other Unit Adjustments - Lennox MERIT ML180UHE Installation Instructions Manual

Model
Gas
Input Size
Nat
045
LP/propane
Nat
070
LP/propane
Nat
090
LP/propane
Nat
110
LP/propane
Nat
135
LP/propane
High Altitude Pressure Switch Kit
Model
Input Size
0−4500 ft
045
070
090 No Change
110
135
NOTE − A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion
procedure.

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 re-
quire no adjustment.
Flame Rollout Switches
These manually reset switches are located on the burner
box.
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
Manifold Pressure Settings at all Altitudes
0−2000 ft
3.5
10.0
3.5
10.0
3.5
10.0
3.5
10.0
3.5
10.0
Pressure Switch and Gas Conversion Kits at all Altitudes
4501−7500 ft 7501 − 10,000 ft
80W52 80W51
80W52 80W51
80W52 80W51
80W57 80W52
80W52 80W51
TABLE 13
2001−4500 ft. 4501−7500 ft
3.2 3.0
10.0 10.0
3.2 2.8
10.0 10.0
3.2 2.7
10 9.6
3.5 3.0
10.0 9.6
3.5 2.9
10.0 9.6
TABLE 14
High Altitude
Natural Gas to LP/Propane
Natural Gas Burner
Orifice Kit
7501 − 10,000 ft 0 − 7500 ft
73W37
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 decrease
the temperature. Decrease the blower speed to increase
the temperature rise. Failure to adjust the temperature rise
may cause erratic limit operation.
Fan Control
The heat fan−on time of 30 seconds is not adjustable. The
heat fan−off delay (amount of time that the blower operates
after the heat demand has been satisfied) may be adjusted
by changing the jumper position across the five pins on the
integrated control. The unit is shipped with a factory fan−off
delay setting of 90 seconds. The fan−off delay affects com-
fort and is adjustable to satisfy individual applications. Ad-
just 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 re-
turn air temperatures; shorter settings provide higher re-
turn air temperatures. See figure 36.
Page 31
Line Pressure in.wg.
7501 − 10,000 ft
3.5
10.0
3.5
10.0
3.5
10.0
3.5
10.0
3.5
10.0
Burner Orifice Kit
7501 − 10,000 ft
70W89 76W15
Min Max
4.5 13.0
11.0 13.0
4.5 13.0
11.0 13.0
4.5 13.0
11.0 13.0
4.5 13.0
11.0 13.0
4.5 13.0
11.0 13.0
LP/Propane to
Natural Gas Burner
Orifice Kit
0 − 7500 ft
73W81