Carrier 50LC 07, Инструкции по обслуживанию и техническому обслуживанию, Страница: 85 / 100

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SEQUENCE OF OPERATION
General
The Carrier Integrated Staging Control Board (ISC) is intended for use with a standard thermostat capable of three cooling
stages. After initial power to the board, a Green LED will blink with a 1 second duty cycle indicating the unit is running
properly. When the unit is not running properly, the Green LED will blink along with Red LED lights. The Red LED
light configuration will indicate the type of error the board has identified.
The ISC board can be remotely shutdown by removing Jumper 4 and wiring to the Remote Shutdown terminal. The
Smoke Control Module can shut down the unit by removing Jumper 3 and wiring to the Smoke Shutdown terminal. A
smoke alarm can be obtained by wiring to the Smoke Alarm terminal.
The crankcase heater will run at all times except when the compressors are running. An auxiliary power supply (24Vac)
available at TB-4 Terminal is provided to power auxiliary equipment. An optional Phase Monitor Relay can be wired to
the PMR terminal by removing Jumper 5.
Ventilation
In the Ventilation/Fan Mode (G on the thermostat), the indoor fan will run at low speed and the damper will operate at
minimum position.
Cooling
In the Cooling Mode, the small and large compressors will be sequenced to maintain the thermostat/DDC temperature
setpoint. The chart below shows the cooling operation based on the following conditions.
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)
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 outdoor-air damper will maintain its current position, only
compressor 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 temperature to drop below 45
_
F, the outdoor-air damper will return
to the minimum position. If the mixed-air temperature continues 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-energized, if installed, as the outdoor-air damper opens and closes.
In field-installed accessory CO2 sensors are connected to the Economizer, a demand controlled ventilation strategy will
begin to operate. As the CO2 level in the zone increases above the CO2 setpoint, the minimum position of the damper will
be increased proportionally. As the CO2 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.