506842-01
Page 31 of 42
Issue 1132
High Altitude
Units may require manifold pressure adjustment at altitudes
above 2000 ft. In some cases, it is necessary to change the
pressure switch to ensure proper combustion. In all cases
(natural gas and LP/propane gas), maximum line pressure
is 13.0” w.c. Refer to 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.
For Safety, shut unit off and remove manometer as soon
as an accurate reading has been obtained. Take care
to replace pressure tap plug.
IMPORTANT
Manifold Pressure Settings and Pressure Switch
Table 12
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.
* Manifold pressure adjustment based on 1020 Btu/ft.³ gas. Consult local utility for actual heating value. Verify by clocking the meter.
