Combustion Air Blower; Primary Limit Control; Rollout Switch (S47); Bcc2−3 Blower Control A15 - Lennox G26 series User Manual

TABLE 5
G26 BLOWER RATINGS 120V 1PH
BLOWER MOTOR
G26Q2
G26Q3
G26Q3/4
G26Q4/5
8−Combustion Air Blower (B6)
All G26 units use a combustion air blower to move air
through the burners and heat exchanger during heating op-
eration. The blower uses a PSC or shaded Pole 120VAC
motor. PSC motors use run capacitors. The motor operates
during all heating operation and is controlled by blower con-
trol A15. The blower operates continuously while there is a
call for heat. The ignition control is prevented from proceed-
ing through the ignition sequence until combustion air blower
operation is sensed by the prove switch.
The pressure switch connected to the combustion air blower
housing is used to prove combustion air blower operation.
The switch monitors air pressure in the blower housing. Dur-
ing normal operation, the pressure in the housing is nega-
tive. If the pressure drops (becomes more positive), the pres-
sure switch opens. When the pressure switch opens, the
ignition control (A3) immediately closes the gas valve to pre-
vent burner operation.
9−Primary Limit Control (S10)
The primary limit (S10) on G26 units is located in the
middle of the heating vestibule panel. When excess heat
is sensed in the heat exchanger, the limit will open. If the
limit is tripped, the furnace control energizes the supply air
blower and de−energizes the gas valve. The limit automati-
cally resets when unit temperature returns to normal. The
switch is factory set and cannot be adjusted. The switch
may have a different setpoint for each unit model num-
ber. However, the setpoint will be printed on the side of
the limit.
LIMIT CONTROL (S10) FOR
G26 SERIES UNITS AND ALTERNATE STYLE
Units may be equipped with either style limit.
INSULATING COVER (s)
FIGURE 13
10−Rollout Switch (S47) −3 Through −6
Flame rollout switch S47 is a SPST N.C. high temperature
limit located on the right side of the burner box assembly (see
figure 14). S47 is wired to the burner ignition control A3.
When S47 senses flame rollout (indicating a blockage
in the combustion passages), the flame rollout switch
trips, and the ignition control immediately closes the
gas valve.
Switch S47 in all G26 units is factory preset to open at
200_F + 12_F (93_C + 6.7_C) on a temperature rise. All
flame rollout switches are manually reset. A kit (#65K60) is
available for G26 −1 and −2 models.
HP CAP
5MFD 370V
1/5
5MFD 370V
1/3
7.5MFD 370V
1/2
3/4 40MFD 370V
FLAME ROLLOUT SWITCH (S47)
11− BCC2−3 Blower Control A15
(−1 and −2 models)
All G26−2 and −1 model units utilize the BCC2-3 blower con-
trol manufactured by Heatcraft. The BCC2-3 is a printed cir-
cuit board which controls the supply air blower and monitors
primary limit and gas valve operation. The control has a
non-adjustable, factory preset fan-on" timing. Fan off" tim-
ing is adjustable. The board is divided into two sections,
120 and 24VAC. Line voltage comes into the board on the
120VAC side. See figure 16.
Fan Timings
Fan off" timing (time that the blower operates after the heat
demand has been satisfied) is determined by the arrange-
ment of a jumper across pins on the BCC2-3 blower control
board. See figure 15. To adjust fan off " timing, gently dis-
connect jumper and reposition across pins corresponding
with new timing. Fan on" time is factory set at 45 seconds
and is not adjustable.
NOTE If fan off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip re-
sulting in frequent cycling of blower. If this occurs, ad-
just blower to longer time setting.
Figure 15 shows the various fan off" timings and how jumper
should be positioned. Unit is shipped with a factory fan off"
setting of 90 seconds. Fan off" time will affect comfort and
efficiency and is adjustable to satisfy individual applications.
The fan off" timing is initiated after a heating demand but not
after a blower or cooling demand (that is, when indoor ther-
mostat switch is changed from ON to AUTO and heating/
cooling demand is not present, the blower stops immediate-
ly).
TIMING
JUMPER
270
150
Page 14
FLAME ROLLOUT
FIGURE 14
FAN-OFF TIME ADJUSTMENT
To adjust fan-off timing:
Remove jumper from BCC2-3 and se-
lect one of the other pin combinations
to achieve the desired time.
TIMING
210
PINS
(seconds)
Leave jumper off for
330 second fan-off timing.
90
FIGURE 15
SWITCH (S47)