FIGURE 40
MANOMETER
G32 UNIT
Page 29
H−High Altitude Derate
See specifications section in this manual for manifold pres
sure settings for installations at altitudes from 0 to 7500ft. (0
to 2286m).
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.
I−Flame Signal
A microamp DC meter is needed to check the flame signal on
the SureLight control. Use a flame signal transducer (part
number 78H5401) available from Lennox to measure the
flame signal, if meter used will not read microamp signal.
Flame (microamp) signal is an electrical current which
passes from the ignition control through the sensor elec
trode during unit operation. Current passes from the sen
sor through the flame to ground to complete a safety circuit.
To Measure Flame Signal:
1 − Set the volt meter to the DC voltage scale. Insert trans
ducer into the VDC and common inputs. Observe cor
rect polarities. Failure to do so results in negative (−)
values.
2 − Turn off supply voltage to control.
3 − Disconnect flame sensor lead from terminal of ignition
control.
4 − Connect (+) lead of transducer to ignition control sen
sor connection.
5 − Connect (−) lead of the transducer to sensor wire.
6 − Turn supply voltage on and close thermostat contacts
to cycle system.
7 − When unit lights, read voltage on meter display. Re
member 1 DC volt = 1 DC microamp.
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
NOTE− The following is a generalized procedure and
does not apply to all thermostat controls.
1 − Blower operation is dependent on thermostat control
system.
2 − Generally, blower operation is set at thermostat sub
base fan switch. With fan switch in ON position, blower
operates continuously. With fan switch in AUTO position,
blower cycles with demand or runs continuously while
heating or cooling circuit cycles.
3 − In all cases, blower and entire unit will be off when the
system switch is in OFF position.
B−Temperature Rise
Temperature rise for G32 units depends on unit input, blow
er speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of AIR TEMP. RISE
°
F" listed on the unit rating plate.
To Measure Temperature Rise:
1 − Place plenum thermometers in the supply and return air
plenums. Locate supply air thermometer in the first hori
zontal run of the plenum where it will not pick up radiant
heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their high
est and steadiest readings, subtract the two readings.
The difference should be in the range listed on the unit
rating plate. If the temperature is too low, decrease
blower speed. If temperature is too high, first check the
firing rate. Provided the firing rate is acceptable, in
crease blower speed to reduce temperature. To
change blower speed taps see the Blower Speed Taps
section in this manual.
C−External Static Pressure
1 − Measure tap locations as shown in figure 40.
2 − Punch a 1/4" diameter hole
in supply upstream of evap
orator and return air ple
nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with perma
gum. Connect the zero end
of the manometer to the discharge (supply) side of the
system. On ducted systems, connect the other end of
manometer to the return duct as above. For systems
with non−ducted returns, leave the other end of the ma
nometer open to the atmosphere.
3 − With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blow
er motor speed to deliver the air desired according to
the job requirements.
4 − Pressure drop must not exceed 0.5" W.C.
5 − Seal around the hole when the check is complete.
D−Blower Speed Taps Leadless Motors
−1 Models
Blower speed tap selection is accomplished by changing the
taps at the blower motor harness connector. Disconnect har
ness connector from motor to expose speed selectors. Blow
er speed selections are listed in table 15.
To Change Blower Speed
1 − Turn off electric power to furnace.
2 − Remove blower access door.
3 − Disconnect blower motor harness from motor.
4 − Pull harness connector and wires through blower ac
cess panel opening.
5 − Select desired speeds for heating and cooling. (Red =
heating, Black = cooling, White = common).
6 − Depress harness connector tab to release wire termi
nal. Select connector location for new speed (refer to
unit wiring diagram). Insert wire terminal until it is se
curely in place.
7 − Replace harness connector to motor .