Lennox GCS16R-651-125

Page 36
P-Blower/Limit Control S10/K25
Check blower control by operating unit through a heating
cycle. If blower recycles after demand is satisfied, control
should be adjusted. In any case, blower off" settings
above 90F will cause the blower to recycle frequently (af
ter a heating cycle) due to residual heat in the heat ex
change assembly. Blower off" settings above 90F may
also cause nuisance trips of secondary limit S10.
Before adjusting control, disconnect all power to unit. To
adjust the blower control, move the FAN ON" lever (figure
13) as needed so the FAN OFF" lever can be set. Con
trols in all GCS16, GCS16R and GCS16H units use a bi
metal surestart heater and the the FAN ON" lever is non
functional. Set the FAN OFF" lever to a position below
90F. Reassemble unit, reconnect power, and operate
unit through a heating cycle. If blower recycles after heat
ing demand, repeat procedure and adjust control to a low
er setting.
The limit setting is factory preset and must not be ad
justed.
VIII-INDOOR BLOWER
OPERATION / ADJUSTMENT
A-Blower Operation
NOTE - The following is a generalized procedure and
does not apply to all thermostat control systems.
1- Blower operation is dependent on the thermostat con
trol system option that has been installed in the
GCS16. Refer to the section Control System Op
tions" for detailed descriptions of blower operation.
2- Generally, blower operation is set at the thermostat
subbase fan switch. With the fan switch in the ON"
position, the blower operates continuously. With the
fan switch in the AUTO" position, the blower cycles
with demand (or, with some control systems, runs
continuously while the heating or cooling circuits
cycle).
3- In most cases, the blower and entire unit will be off
when the system switch is in the OFF" position. The
only exception is immediately after a heating demand
until blower control switches off.
B-Determining Unit CFM
1- The following measurements must be made with a dry
indoor coil. Run the blower without the cooling de
mand. Air filters must be in place when measure
ments are taken.
2- Measure static pressure external to the unit (from sup
ply to return).
To Measure Discharge Static Pressure:
a- Measure tap locations as shown in figure 36.
b- Punch a 1/4" diameter hole. Insert manometer
hose flush with the inside edge of hole or insula
tion. Seal around the hole with permagum. Con
nect the zero end of the manometer to the dis
charge (supply) side of the system. Connect the
other end of the manometer to the return duct as
above.
c- With only the blower motor running, observe the
manometer reading.
d- Seal around the hole when the check is complete.
3- The CFM can be adjusted by changing the motor
speed taps. Follow the blower speed change instruc
tions below.
FIGURE 36
STATIC PRESSURE TAP LOCATIONS
MANOMETER
UNIT
C-Blower Speed Adjustment
208v/230v ONLY
All -261, -311, -411 and -413 units (208/230V only) have
four speed leadless blower motors. The speed ports are
arranged as shown in table 17.
TABLE 17
FOUR SPEED BLOWER MOTORS
Speed Tap Number
Low
Medium-Low
Medium-High
High
Common
5
4
3
2
1
All -511, -513, -651 and -653 units (208/230V only) have
five speed leadless blower motors. The speed ports are
arranged as shown in table 18.