Lennox B050A3B, Installation/Servicing Instructions And Users Information Manual

Page: 19 / 36

506307-01 Page 19 of 36 Issue 1207
Check with your local gas company to find out if the gas
supply in your area is derated. Gas deration negates the
necessity of performing any adjustment on the furnace.
If your gas supply is not derated, and regardless of the
type of gas used, installation of this furnace at elevations
above 2,000 ft. requires a n input reduction at the rate of
four percent (4%) for each 1,000 ft. above sea level.
Unless an orifice change is specified by an applicable
code, or the furnace is to be installed above 6,999 feet, the
recommended method of altitude derating this furnace is to
appropriately lower your manifold pressure. The appropriate
manifold pressures based on the elevation and the heating
value can be found in Table 6.
If local codes require an orifices change or if the furnace
installation is above 6,999 feet. The appropriate orifice size
based on the elevation and the heating value can be found
in Table 7. Sizing of the orifice must be based o the previously
mentioned 4% derate for each 1,000 feet for installations at/
or above 2,000 feet rule and the orifices must be drilled in
such a way as to assure concentricity.
Hand drilling of
orifices is unacceptable.
For installation above 2,000 feet if unit is adjusted for
altitude mark the furnace label that has the words “Altitude
Adjusted” .
Hand drilling of orifices is never acceptable since it could
lead to delayed igntion, overfiring, improper combustion,
flashback and flame rollout. All these conditions could
lead to a fire hazard and bodily harm, or loss of life.
WARNING
Blower Adjustment Checkout:
Prior to any blower adjustment, electrical service must
be turned OFF.
This furnace is equipped with a 3 speed direct drive
motor to deliver a temperature rise within the range specificed
on the rating label, between the return and supply plenums,
at the external duct static pressure noted on the rating label.
Adjust the blower speed so that the temperature rise is
within the rise specified on the rating label. Consult the wiring
diagram for speed changes on the direct drive motor.
Limit Control Checkout:
After the furnace has been in operation for at least 15
minutes, restrict the return air supply by blocking the filters
or closing the return registers and allow the furnace to shut
down on hight limit. The main burners will shut OFF and the
main blower and combustion blower should continue to run.
Remove the restriction and the burners should come back
on in a few minutes.
Flame Rollout Switch:
This unit is equipped with two (2) manual reset flame-
rollout switches that protects against improper venting of
the flue gases from the heat exchanger due to blockage
causing heat (or flames) to “rollout” into the burner box from
the heat exchangers, either safety device will activate and
shut off power to the automatic gas valve before there is
damage to the furnace. The loss of power to the gas vlave
will shut off the gas burners. Should this occur, it will be
necessary to determine the cause of the rollout, correct the
condition that caused it, and reset the flame-rollout switch
The furnace should be allowed to cool-off before
attempting to reset the switch. Failure to follow these
instructions could result in injury due to burns.
WARNING
Table 6
High Altitude Manifold Pressure Derate
(with standard 42 orifice Natural / 54 orifice LP sizes)
High Altitude Orifice Size Derate
Table 7