Carrier WeatherExpert 48LC B14 Series, Руководство по установке

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Low Ambient Cooling Operation Down to 45°F (7°C)
In Low Ambient RTU conditions when the temperature is be-
tween 55°F (13°C) and 45°F (7°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 out-
door-fans will run in the standard cooling mode. If the Outdoor
Fan Select Switch (see Fig. 52) is in the up 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 down position, the out-
door fans will run in the Minimum Fan Speed Mode (MIN) set to
160 rpm regardless of the cooling demand.
At temperatures below 45°F (7°C), unit will utilize economizer
for SA temperature control.
48LC Size 14 through 26 Units have a SPST normally open Low
Ambient Switch wired across the TS and OF terminal and a jump-
er placed across the PS terminal (see Fig. 53). 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.
Table 9 shows the operation of the outdoor fan for each unit.
Fig. 52 — Outdoor Fan Speed Select Switch
Fig. 53 — Schematic of SPST Low Ambient Switch
Heating
In the Heating Mode (W1 and G), the ISC board sends power to
W on the IGC board. 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 “hall effect” sensor,
the ignition activation period begins. The burners will ignite with-
in 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 VAV-RTU Open.
When gas ignition occurs, the IGC board will continue to monitor
the condition of the rollout switch, the limit switches, the “hall ef-
fect” sensor, 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. The indoor
fan motor will continue to operate for an additional 45 seconds
then stop. If the overtemperature 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 zones are satis-
fied, the gas valve closes, interrupting the flow of gas to the main
burners.
Morning Warm-up
The control will provide a Morning Warm-up cycle the first time
if transition from unoccupied to occupied and if the heating is re-
quired and the unit goes into heating immediately. Whenever the
unit enters the heating mode, before any heat stage is enabled,
the control will provide a Linkage mode to the system that will
cause the terminals to maintain sufficient airflow. The Linkage
mode of Warm-up (2) will be sent to the terminal system to in-
sure sufficient airflow while in the heating mode but also provid-
ing a controlled warm-up cycle to prevent overheating of some
zones. As a safety measure, should the heating cycle continue
and the SAT approach the “Maximum Heating SAT” limit, the
Linkage mode sent will change to Pressurization (6) to insure all
terminals open to their maximum airflow. The Linkage mode
will remain Pressurization until that heating cycle ends. Once the
heating demand is met and the heat cycle is completed or if cool-
ing is required, heating will be locked out until the beginning of
the next occupied period.
Occupied Heating
Optionally, the user may enable occupied heating which will allow
heating whenever heating is needed during the occupied period.
The cycle will operate exactly the same as Morning Warm-up
above, except it will not be limited by the transition into an occu-
pied period.
Table 9 — Low Ambient Temperature Outdoor Fan
Control
48LC
UNIT
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
OF SPEED
SELECT
ON
FCS
MIN
OFF
JUMPER ON
LAS
SPST
PS PS
TS OF