Unit Components; Control Box; Control Transformer T1; I Application - Lennox G21Q3-40 Unit Information

I − APPLICATION
G21/GSR21 unit input range covers 40,000 through 100,000
Btuh. See specifications table.
G21/GSR21 models use the same cabinet size as the ex
isting G14/GSR14 furnace line. All units in the
G21/GSR21 series use direct drive blowers and accept
cooling coils in nominal tonnages up to 5 tons for the 80,
100. Consult the Engineering Handbook for proper sizing.
Slab filters are used for either bottom or side return air in
G21 models and top return air in GSR21 models.
II − UNIT COMPONENTS
A − Control Box (Figures 1 and 2)
The G21 control box is located below the air intake chamber.
40, 60 and 80 control boxes are designed to open over the
exhaust PVC line when the unit is set up for right hand dis
charge of exhaust. 100 control boxes are designed to open
over the exhaust PVC line when the unit is set up for left hand
discharge of exhaust.
The GSR21 control box is located in the lower right hand
corner of the heating compartment in horizontal installa
tions and in the upper right hand corner of the heating
compartment in reverse flow applications.
GSR21Q CONTROL BOX
TERMINAL
STRIP
TB1
TERMINAL
BLOCK
TB2
FAN TIMING CONTROL
(A28)
INDOOR
BLOWER
RELAY (K3)
TRANSFORMER
T1
GSR21V CONTROL BOX
TERMINAL STRIP
TB1
TERMINAL BLOCK
TB2
ACCESSORY
RELAY K109
TRANSFORMER
T1
FIGURE 1
GROUNDING LUG
DOOR INTERLOCK
SAFETY SWITCH
(S51)
GROUNDING LUG
DOOR INTERLOCK
SAFETY SWITCH
(S51)
Page 12
G21Q CONTROL BOX
FAN TIMING CONTROL
(A28)
TRANSFORMER T1
TERMINAL STRIP TB1
G21V CONTROL BOX
TRANSFORMER
T1
TERMINAL BLOCK TB2
FIGURE 2
1 − Control Transformer T1
A transformer (T1) located inside the control box provides
power to the low voltage section of the unit. Transformers are
rated at 30VA for Q" models and 50VA for V" models with a
120V primary and 24V secondary.
2 − Transformer Fuse F1
Transformer T1 is protected by a fuse F1. See table 1 for fuse
ratings. The fuse is located on the TB1 terminal strip.
TRANSFORMER FUSE
APPLICATION
F1
V" MODELS
Q" MODELS
GROUNDING
LUG
TERMINAL
BLOCK
INDOOR BLOWER
RELAY K3
ACCESSORY
RELAY K109
GROUNDING
LUG
TERMINAL
STRIP TB1
TABLE 1
FUSE RATING
3 AMP MDX SLOW BLOW
2 AMP AGC FAST BLOW
TB2