40
In field--installed accessory CO
2
sensors are connected to
the Economizer, a demand controlled ventilation strategy
will begin to operate. As the CO
2
level in the zone
increases above the CO
2
set--point, the minimum position
of the damper will be increased proportionally. As the
CO
2
level decreases because of the increase of fresh air,
the outdoor--air damper will be proportionally closed. For
economizer operation, there must be a thermostat call for
the fan (G). If the unit is occupied and the fan is on, the
damper will operate at minimum position. Otherwise, the
damper will be closed.
Low Ambient Cooling Operation Down to 40
_
F (4
_
C)—
In Low Ambient RTU conditions when the temperature is
between 55
_
F (13
_
C) and 40
_
F (4
_
C), the Low Ambient
Switch (LAS) will be active and the outdoor fans will run
to the pre--set factory outdoor--fan speed. When the
temperature is greater than 65
_
F (18
_
C), the Low
Ambient Switch will deactivate and the outdoor fans will
run in the standard cooling mode. If the Outdoor Fan
Select Switch (see Fig. 44) is in the ON position, the
outdoor fans will run in the Fan Cycle Speed Mode (FCS)
set to 250 rpm. If the Outdoor Fan Select Switch is in the
OFF position, the outdoor fans will run in the Minimum
Fan Speed Mode (MIN) set to 160 rpm regardless of the
cooling demand.
LC Size 14 through 26 units have a SPST normally open
Low Ambient Switch wired across the TS and OF terminal
and a jumper placed across the PS terminal (see Fig. 45).
When the LAS is active, the switch will close making
contact to the OF terminal. This is done for units that require
all outdoor fans to run at the same pre--set factory Low
Ambient Speed.
OF SPEED
SELECT
ON
FCS
MIN
OFF
a48--- 9341
Fig. 44 -- Outdoor Fan Speed Select Switch
JUMPER ON
LAS
SPST
PS
PS
TS
OF
C13328
Fig. 45 -- Schematic of SPST Low Ambient Switch
The Low Ambient Temperature Outdoor Fan Control
Table (below) shows the operation of the outdoor fan for
each unit.
Table 8 – Low Ambient Temperature Outdoor Fan Control
LC Size
No. of
Fans On
No. of
Fans Off
Switch
Outdoor Fan
Select Switch
RPM
14
3
0
SPST
Up
250
17
4
0
SPST
Up
250
20
4
0
SPST
Up
250
24
6
0
SPST
Up
250
26
6
0
SPST
Up
250
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 controlled 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 ignite within 5 seconds. If the burners do not
light, there is a 22--second delay before another 5--second
attempt. This sequence is repeated for 15 minutes or until the
burners light. If, after the 15 minutes, the burners still have
not lit, heating is locked out. To reset the control, break
24VAC 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 fan motor will continue to
operate for an additional 45 seconds then stop. If the over
temperature limit opens after the indoor motor is stopped,
but within 10 minutes of W1 becoming inactive, on the
next cycle the time will be extended by 15 seconds. The
maximum 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 satisfied, the gas valve closes,
interrupting the flow of gas to the main burners.
Summary of Contents for WeatherExpert 48LC
Page 5: ...5 C13057 Fig 2 Unit Dimensional Drawing 14 Size Unit Sheet 1 of 3 ...
Page 6: ...6 C13058 Fig 2 cont Unit Dimensional Drawing 14 Size Unit Sheet 2 of 3 ...
Page 7: ...7 C13059 Fig 2 cont Unit Dimensional Drawing 14 Size Unit Sheet 3 of 3 ...
Page 8: ...8 C13032 Fig 3 Unit Dimensional Drawing 17 and 20 Size Units Sheet 1 of 3 ...
Page 9: ...9 C13033 Fig 3 cont Unit Dimensional Drawing 17 and 20 Size Units Sheet 2 of 3 ...
Page 10: ...10 C13034 Fig 3 cont Unit Dimensional Drawing 17 and 20 Size Units Sheet 3 of 3 ...
Page 11: ...11 C14106 Fig 4 Unit Dimensional Drawing 24 and 26 Size Units Sheet 1 of 3 ...
Page 12: ...12 C14107 Fig 4 cont Unit Dimensional Drawing 24 and 26 Size Units Sheet 2 of 3 ...
Page 13: ...13 C14108 Fig 4 cont Unit Dimensional Drawing 24 and 26 Size Units Sheet 3 of 3 ...
Page 17: ...17 C13054 Fig 8 Roof Curb Details 14 Size Unit ...
Page 18: ...18 C13055 Fig 9 Roof Curb Details 17 and 20 Size Units ...
Page 19: ...19 C13056 Fig 10 Roof Curb Details 24 and 26 Size Units ...
Page 27: ...27 a48 9336 Fig 26 48LC 14 26 Electro mechanical Control Wiring Diagram ...
Page 28: ...28 a48 9337 Fig 27 48LC 14 26 RTU Open Control Wiring Diagram ...
Page 29: ...29 a48 9338 Fig 28 48LC 14 26 SystemVut Control Wiring Diagram ...
Page 31: ...31 a48 9339 Fig 30 Typical Power Wiring Diagram SystemVut Controls 48LC 26 208 230V Shown ...
Page 58: ...58 a48 9340 Fig 55 Typical EconoMi erR X Wiring Diagram ...