High Altitude
The manifold pressure may require adjustment to ensure proper combustion at higher altitudes. Refer to Table 12 for manifold pressure and pressure switch change.
IMPORTANT
For Safety, shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to replace pressure tap plug.
Manifold Pressure Settings and Pressure Switch
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.
NOTE: For Altitudes of 7501' - 10,000' call Lennox Technical Support Product Applications.
Table 12
Other Unit Adjustments
Primary and Secondary Limits
The primary limit is located on the heating compartment vestibule panel. The secondary limits (if equipped) are located 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 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 allowing 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 45 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 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 deenergized. Longer off delay settings provide lower return air temperatures; shorter settings provide higher return air temperatures. See Figure 37.
HEAT FAN OFF TIME IN SECONDS
Figure 37
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