Back; High Altitude Information; Other Unit Adjustments - Lennox G71MPP Installation Instructions Manual

High Altitude Information

NOTE − In Canada, certification for installations at eleva-
tions over 4500 feet (1372 m) is the jurisdiction of local au-
thorities.
G71MPP units require no manifold pressure adjustments
for operation at altitudes up to 10,000 feet (3048m) above
sea level. Units installed at altitude of 7,501 to 10,000 feet
(2287 to 3048m) require a pressure switch change per
table 33. Table 33 lists conversion kit requirements,
LP/Propane
Kit
Model
Input
0 − 10,000
Size
(0 − 3048 m) (0 − 2286 m)
−070
−090
33W41 Not required
−110
−135
NOTE − Pressure switch is factory set. No adjustment necessary. All models use the factory installed pressure switch from 0−7,500 feet (0− 2286m).
NOTE − See previous page for manifold pressure measurement procedure.

Other Unit Adjustments

Primary and Secondary Limits
The primary limit is located on the heating compartment
vestibule panel. The secondary limits are located in the
blower compartment, attached to the back side of the blow-
er. These limits are factory set and require no adjustment.
Flame Rollout Switches (Two)
These manually reset switches are located on the burner
box. If tripped, check for adequate combustion air before
resetting.
Pressure Switches (Three)
The pressure switches are located in the heating compart-
ment on the combustion air inducer. These switches check
for proper combustion air inducer operation before allow-
ing ignition trial. The switches are factory−set and require
no adjustment.
Back−Up Secondary Limit (090, 110 and 135)
The back−up secondary limit is located on the combustion
air inducer. This switch protects the plastic components
from overheating due to indoor blower motor failure. If
tripped, check for proper blower operation before resetting.
Temperature Rise
After the furnace has been started and supply and return air
temperatures have been allowed to stabilize, check the
temperature rise with the unit operating at 100 percent fir-
ing rate. 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.
Conversion Kit Requirements and Manifold Test Pressures
High Altitude Pressure
Switch Kit
7,501 − 10,000
0 − 7,500
(2287 −
3048m)
36W77
40W05
40W06
40W07
pressure switch requirements and manifold pressures at
all altitudes.
NOTE − The values given in table are measurements only.
The gas valve should not be adjusted.
The combustion air pressure switch is factory−set and re-
quires no adjustment.
NOTE − A natural to L.P. propane gas changeover kit is nec-
essary to convert this unit. Refer to the changeover kit
installation instruction for the conversion procedure.
TABLE 33
Manifold Pressure at All Altitudes (in. w.g.)
Low Fire
(40% rate)
Natural Gas LP/Propane
0.7 2.0
Thermostat Heat Anticipation
Set the heat anticipator setting (if adjustable) according to
the amp draw listed on the wiring diagram that is attached
to the unit.
Electrical
1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating).
3 − Check amp-draw on the blower motor.
Motor Nameplate__________Actual__________
NOTE − Do not secure the electrical conduit directly to the
air ducts or structure.
Electronic Ignition
The integrated control has an added feature of an internal
Watchguard control. The feature serves as an automatic re-
set device for ignition control lockout caused by ignition fail-
ure. This type of lockout is usually due to low gas line pres-
sure. After one hour of continuous thermostat demand for
heat, the Watchguard will break and remake thermostat de-
mand to the furnace and automatically reset the control to
begin the ignition sequence.
Exhaust and Air Intake Pipe
1 − Check exhaust and air intake connections for tightness
and to make sure there is no blockage.
2 − Are pressure switches closed? Obstructed exhaust
pipe will cause unit to shut off at pressure switches.
Check termination for blockages.
3 − Reset manual flame rollout switches on burner box
cover.
Page 56
High Fire
(100% rate)
Natural Gas LP/Propane
3.5 10.0