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I-UNIT COMPONENTS (Figures 1)
G17 unit components are shown in figure 1. The blower
controls, gas valve and burners can be accessed by reĆ
moving the upper access panel.
G17 units are factory equipped with bottom return air panels
and bottom side return air panels in place. The panels are deĆ
signed to be field removed as required for bottom air return or
side air return. All X models are factory equipped with the botĆ
tom return air panel removed.
DANGER
Possibility of exhaust gas recirculation.
X models are factory equipped with bottom return
air panel removed. If opening is not used and if
not properly sealed, exhaust gases can recircuĆ
late through the opening and enter supply air
stream resulting in personal injury or death.
A-Control Box Components(Figure 3)
On G17 series units the unit control box is located in the
blower compartment between the burner box and the blowĆ
er housing. The hinged control box can be lowered for serĆ
vice access by removing two securing screws, one located
on either side. At the top right corner of the control box is the
door interlock switch (S51).
Housed in the control box are the unit transformer (T1) and
BCC2-2 blower control (A15).
G17 CONTROL BOX Ć FRONT VIEW
DAMPER
DOOR
BLOWER
BCC2-2
CONTROL
A15
TRANSFORMER
T1
FIGURE 3
DOOR
INTERLOCK
S51
1- Control Transformer (T1)
A transformer located inside the control box provides powĆ
er to the low voltage section of the unit. Transformers on all
models are rated 30VA with a 120V primary and a 24V secĆ
ondary.
2- BCC2-2 Blower Control (A15)
All G17 units utilize the BCC2-2 blower control. The
BCC2-2 is a printed circuit board which controls the blower
and monitors primary limit and gas valve operation. The
control has a non-adjustable, factory preset on" fan timĆ
ing. Fan off" timings are adjustable. The board is divided
into two sections, 120 and 24VAC. Line voltage comes into
the board on the 120VAC side. See figure 2.
CAB" and XFMR " send 120VAC to the damper motor and
transformer, respectively. The active cooling and heating
blower speed terminals and three dummy D" terminals are
located on the 120VAC side of the BCC2-2. Also located on
the 120VAC side of the control are neutral terminals and a
terminal for accessories such as an electronic air cleaner.
24VAC comes from the transformer into terminal 24V" on
the 24VAC side of the BCC2-2. Thermostat connections
and safety circuit terminals are also located on the 24VAC
side of the control. Fan off" timings may be adjusted by
changing the position of a jumper across terminal pins.
The CF" terminal provides 120VAC power for continuous
fan option or other accessories.
Later production units are equipped with a 3A fuse located
inline between the transformer and terminal XFMR on the
blower control. The fuse provides overcurrent protection
to all components located in the low voltage control circuit.
Fan Timings
DANGER
Shock hazard. Avoid control damage or personĆ
al injury. Make sure to disconnect power before
changing fan off" timings.
FIGURE 4
FANĆOFF TIME ADJUSTMENT
270
210
150
90
To adjust fan-off timings:
Remove jumper from BCC2 and select
one of the other pin combinations to
achieve the desired time.
TIMING
JUMPER
TIMING PINS
(seconds)
Leave jumper off to
achieve
330 second fan-off timing.
NOTEĊIf fan off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip reĆ
sulting in frequent cycling of blower. If this occurs, adĆ
just blower to longer time setting.
