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OF SPEED
SELECT
Fig. 56 — Outdoor Fan Speed Select Switch
OF
24VAC
TB-4
LAS
SPDT
Fig. 57 — Schematic of SPDT Low Ambient Switch
Table 9 shows the operation of the outdoor fan for size 08, 09 and
12 units.
Table 9 — Low Ambient Temperature Outdoor Fan
Control
48LC
NO. OF
NO. OF
SIZE
FANS ON
FANS OFF
08
2
1
09
2
1
12
2
1
Heating
In the Heating Mode (W1 and G on the thermostat), the ISC board
sends power to W on the IGC board. Assuming the unit is con-
trolled through a room thermostat set for fan auto, the indoor fan
motor will energize and the outdoor-air dampers will open to their
minimum position. The ISC board upon seeing W1 and G ON will
turn the indoor fan to high speed.
The IGC board starts its gas ignition process. A check is made to
ensure that the rollout switch and limit switch are closed. If the
check was successful, the induced draft motor is energized, and
when its speed is satisfactory, as proven by the flue gas pressure
switch, the ignition activation period begins. The burners will ig-
nite within 5 seconds. If the burners do not light, there is a 22-sec-
ond delay before another 5-second attempt. This sequence is re-
peated for 15 minutes or until the burners light. If, after the 15
minutes, the burners still have not lit, heating is locked out. To re-
set the control, break 24 vac power to the thermostat.
When gas ignition occurs, the IGC board will continue to monitor
the condition of the rollout switch, the limit switches, the flue gas
pressure switch, as well as the flame sensor.
When W1 is turned OFF, the IGC board turns off the gas valve.
The IGC board has a delay time before it turns IFO=OFF. At this
time, the ISC board sees W1=OFF and IFO=ON. The ISC will
keep the indoor fan ON high speed. Once the IGC board delay
times out, the ISC board will see W1=OFF and IFO=OFF, which
then turns the indoor fan OFF.
If the call for W1 lasted less than 1 minute, the heating cycle will
not terminate until 1 minute after W1 became active. If the unit is
controlled through a room thermostat set for fan auto, the indoor
All manuals and user guides at all-guides.com
ON
FCS
MIN
OFF
ODF RELAY
PS
PS
REMOVE JUMPER
OUTDOOR FAN
SWITCH
SELECT
SWITCH
(1) SPDT
Down
(1) SPDT
Down
(1) SPDT
Down
fan motor will continue to operate for an additional 45 seconds
then stop. If the over temperature limit opens after the indoor mo-
tor is stopped, but within 10 minutes of W1 becoming inactive, on
the next cycle the time will be extended by 15 seconds. The maxi-
mum delay is 3 minutes. Once modified, the fan OFF delay will
not change back to 45 seconds unless power is reset to the control.
A LED indicator is provided on the IGC to monitor operation.
When additional heat is required, W2 closes and initiates power to
the second stage of the main gas valve. When the thermostat is sat-
isfied, the gas valve closes, interrupting the flow of gas to the main
burners.
EconoMi$er
®
The EconoMi$er X system is an expandable economizer control
system, which includes a W7220 economizer module (controller)
with an LCD and keypad (see Fig. 58). The W7220 can be config-
ured with optional sensors.
RPM
Fig. 58 — W7220 Economizer Module
160
The W7220 economizer module can be used as a stand-alone
160
economizer module wired directly to a commercial set-back space
160
thermostat and sensors to provide outside air dry-bulb economizer
control.
The W7220 economizer module can be connected to optional
sensors for single or differential enthalpy control. The W7220
economizer module provides power and communications for the
sensors.
The W7220 economizer module automatically detects sensors by
polling to determine which sensors are present. If a sensor loses
communications after it has been detected, the W7220 economizer
controller indicates a device fail error on its LCD.
SYSTEM COMPONENTS
The EconoMi$er X system includes an economizer module, 20k
mixed air sensor, damper actuator, and either a 20k outdoor air
temperature sensor or S-Bus enthalpy sensors.
Economizer Module
The module is the core of the EconoMi$er X system. The module
is mounted in the unit's control box, and includes the user
interface for the system. The W7220 economizer module provides
the basic inputs and outputs to provide simple economizer control.
When used with the optional sensors, the economizer module
provides more advanced economizer functionality.
S-Bus Enthalpy Control Sensors
The sensor is a combination temperature and humidity sensor
which is powered by and communicates on the S-Bus. Up to three
sensors may be configured with the W7220 economizer module.
CO
Sensor (optional)
2
The CO
sensor can be added for Demand Controlled Ventilation
2
(DCV).
34
X (Factory Option)
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