Lennox G21Q Series Unit Information

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
FANOFF 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.
Fanoff timing is factory
set at 270 seconds
NOTEIf 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 − LimitControl−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 selfresetting 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.

Lennox G21Q Series Specifications

General

Brand	Lennox
Model	G21Q Series
Category	Industrial Equipment
Language	English