63
Ventilation
In the Ventilation/Fan Mode (G on the thermostat), the indoor
fan will run at low speed and the damper will operate at mini-
mum position.
Cooling
In the Cooling Mode, the small and large compressors will be
sequenced to maintain the thermostat/DDC temperature set-
point. The chart below shows the cooling operation based on
the following conditions.
The outdoor fan and VFD controlled indoor-fan will operate at
low, medium and high speed. The indoor-fan speed (rpm) is
factory set by the CFM and static pressure requirements for the
unit installed.
Economizer (Optional)
When the economizer is in Free Cooling Mode and a demand
for cooling exists (Y1 on the thermostat), the economizer will
modulate the outdoor-air damper to provide a 50°F (10°C) to
55°F (13°C) mixed-air temperature into the zone and run the
indoor-fan at high speed. As mixed-air temperature fluctuates
above 55°F (13°C) or below 50°F (10°C), dampers will be
modulated (open or close) to bring the mixed-air temperature
back within control. Upon more call for cooling (Y2 on the
thermostat), the outdoor-air damper will maintain its current
position, compressor C1 will run and the outdoor fan will run
at low speed. If there is further demand for cooling, the out-
door-air damper will maintain its current position, only com-
pressor C2 will run and the outdoor fan will run at medium
speed. The VFD-controlled indoor fan will operate at high
speed regardless of the cooling demand.
If the increase in cooling capacity causes the mixed-air tem-
perature to drop below 45°F, the outdoor-air damper will return
to the minimum position. If the mixed-air temperature contin-
ues to fall, the outdoor-air damper will close. Once the mixed
air temperature rises above 48°F (9°C), the control returns to
normal. The power exhaust fans will be energized and de-ener-
gized, if installed, as the outdoor-air damper opens and closes.
If field-installed accessory CO
2
sensors are connected to the
economizer, a demand controlled ventilation strategy will be-
gin to operate. As the CO
2
level in the zone increases above the
CO
2
setpoint, the minimum position of the damper will be in-
creased proportionally. As the CO
2
level decreases because of
the increase of fresh air, the outdoor-air damper will be propor-
tionally closed. For economizer operation, there must be a ther-
mostat 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 be-
tween 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. 64) 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 posi-
tion, the outdoor fans will run in the minimum fan speed mode
(MIN) set to 160 rpm regardless of the cooling demand.
Fig. 64 — Outdoor Fan Speed Select Switch
The 50LC size 14-26 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. 65). 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.
The low ambient outdoor fan control chart (listed in Table 29)
shows the operation of the outdoor fans for each unit
Fig. 65 — Schematic of SPST Low Ambient Switch
Table 29 — Low Ambient Temperature Outdoor Fan
Control
Heating
In the Heating Mode (W1 on the thermostat), power is applied
to the G and W1 terminal at the ISC board and energizes the
first state of electric heat. Upon more call for heat (W2 at the
thermostat), power is applied to the G and W2 terminal at the
ISC board and energizes the second state of electric heat. The
VFD controlled indoor fan will operate at high speed regard-
less of the heating demand.
INPUT OUTPUT
Thermostat Compressor
C1
Compressor
C2
Indoor
Fan
Speed
Outdoor
Fan
Speed
First
Stage
Cooling
(Y1)
On
Off
Low
Low
(700 rpm)
Second
Stage
Cooling
(Y2)
Off On
Medium
Medium
(800 rpm)
Third
Stage
Cooling
(Y3)
On On
High
High
(1,000 rpm)
50LC
SIZE
NO. OF
FANS
ON
NO. OF
FANS
OFF
SWITCH LAS FIG.
NO.
OF
SELECT
SWITCH
RPM
014
3
0
(1) SPST
66
Up
250
017
4
0
(1) SPST
66
Up
250
020
4
0
(1) SPST
66
Up
250
024
6
0
(1) SPST
66
Up
250
026
6
0
(1) SPST
66
Up
250
OF SPEED
SELECT
ON
FCS
MIN
OFF
JUMPER ON
LAS
SPST
PS
PS
TS
OF
Summary of Contents for 50LC 14
Page 26: ...26 Fig 34 50LC 14 26 Control Wiring Diagram...
Page 27: ...27 Fig 35 50LC 14 26 RTU Open Control Wiring Diagram...
Page 28: ...28 Fig 36 50LC 14 20 208 230V 3 Phase Power Wiring Diagram...
Page 29: ...29 Fig 37 50LC 24 26 208 230V 3 Phase Power Wiring Diagram...
Page 30: ...30 Fig 38 50LC 14 26 460V 575V 3 Phase Power Wiring Diagram...