Page 19
b−HEATING BLOWER"
Place the
HEATING BLOWER
jumper across the first and
second pins for single−stage heating operation (position
#1). For two−stage operation, place the jumper across the
second and third pins (position #2).
The position of the jumper determines which set of speed
jumpers is activated. When the
HEATING BLOWER
jumper
is across the first and second pins, the
HEAT
jumper selec
tions are activated when W1 is energized.
If the jumper is across the second and third pins, the
LOW
jumper selections are activated when W1 is energized.
HEAT
jumper selections are activated when W2 is ener
gized.
NOTE−In Harmony II zoning applications, HEATING
BLOWER jumper must be in position #2.
c−HEAT"
The
HEAT
jumper is used to set the blower speed to obtain
the required CFM as outlined in HEAT SPEED section of
the tables on pages 7 and 8.
If a lower heating speed (than one that is listed in HEAT
SPEED section) is required, the
LOW
jumper may be used
to set the heating speed. This is done by first placing the
LOW
jumper in the desired CFM position and then placing
the
HTG. BLOWER
jumper across the second and third
pins (regardless of the actual stage). Doing so will activate
the low speed jumper setting when W1 is energized.
d−HIGH"
The
HIGH
jumper is used to determine the CFM during
cooling speed. These jumper selections are activated
when G and DS terminals are energized.
e−LOW"
The
LOW
jumper is used to determine CFM during low
speed cooling. These jumper selections are activated
when G is energized. The
LOW
jumper may also be used
for low speed heating. See the HEAT" section for details.
f−FAN OFF"
Fan OFF" timings (time that the blower operates after the
heat demand has been satisfied) are determined by the ar
rangement of a jumper on the VSP2−1 board. See fig
ure 15. To adjust fan OFF" timings, gently disconnect the
jumper and reposition it across pins corresponding with the
new timing. Fan OFF" time is factory set at 270 seconds.
Fan ON" time is factory set at 45 seconds and is not adjust
able.
WARNING − MAKE SURE TO DISCONNECT POWER
BEFORE CHANGING FAN OFF" TIMINGS.
FIGURE 15
FANOFF TIME ADJUSTMENT
270
210
150
90
To adjust fan−off timings:
Remove jumper from VSP2−1 and
select one of the other pin combina
tions to achieve the desired time.
TIMING
JUMPER
TIMING PINS (seconds)
Leave jumper off to achieve
330 second fan−off timing.
Fanoff timing is factory
set at 270 seconds
NOTEIf fan OFF" time is too low, residual heat in heat
exchanger may cause primary limit S10 to trip resulting in
frequent cycling of blower. If this occurs, adjust blower to
longer time setting.
C − LimitControl−Modulation/Limit
Control (Figure 16)
S78 N.O.
HONEYWELL LIMIT CONTROL− MODULATION/
LIMIT CONTROL ALL MODELS S10/S78
FIGURE 16
S78
N.C.
S10
S10
S78 SWING
S78 N.C. IS
A 1/4"
QUICK
CONNECT
1 − Limit Control (S10) Q" Models
G21Q/GSR21Q models use a Honeywell limit control. See
unit components illustration (page 11) for exact location. If heat
exchanger temperatures rise above limit setting (see table 5),
the selfresetting limit interrupts power to ignition control A3,
and fan timing control A28 will maintain the blower to cool
down the unit. This is a safety shut down function. S10 auto
matically resets when temperatures inside the heat exchange
assembly drop below limit setting. Do not change factory limit
setting. S10 is set to limit maximum discharge air temperature.
