Lennox International Inc Merit Series Gas Furnace installation instructions Other Unit Adjustments

TABLE 12

Manifold Pressure Settings at all Altitudes

Model	Gas	0−2000 ft	2105−4500 ft.	4501−7500 ft	7501 − 10,000 ft	Line Pressure in.wg.
Input Size						Min	Max
045	Nat	3.5	3.2	3.0	3.5	4.5	13.0
	LP/propane	10.0	10.0	10.0	10.0	11.0	13.0
070	Nat	3.5	3.2	2.8	3.5	4.5	13.0
	LP/propane	10.0	10.0	10.0	10.0	11.0	13.0
090	Nat	3.5	3.2	2.7	3.5	4.5	13.0
	LP/propane	10.0	10	9.6	10.0	11.0	13.0
110	Nat	3.5	3.5	3.0	3.5	4.5	13.0
	LP/propane	10.0	10.0	9.6	10.0	11.0	13.0
135	Nat	3.5	3.5	2.9	3.5	4.5	13.0
	LP/propane	10.0	10.0	9.6	10.0	11.0	13.0

TABLE 13

Pressure Switch and Gas Conversion Kits at all Altitudes

Model

Input Size

			High Altitude	Natural Gas to LP/Propane		LP/Propane to
High Altitude Pressure Switch Kit			Natural Gas Burner			Natural Gas Burner
				Burner Orifice Kit
			Orifice Kit			Orifice Kit
0−4500 ft	4501−7500 ft	7501 − 10,000 ft	7501 − 10,000 ft	0 − 7500 ft	7501 − 10,000 ft	0 − 7500 ft

045		80W52	80W51
070		80W52	80W51
090	No Change	80W52	80W51	73W37	70W89	76W15	73W81
110		80W57	80W52
135		80W52	80W51

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

This manually reset switches are located on the top of 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

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 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 in- tegrated 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.

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