Carrier 48TC*D08 - Manual (Page 76)

76
DCV operation is available in Occupied and Unoccupied
periods with EconoMi$er IV. However, a control
modification will be required on the 48TC unit to
implement the Unoccupied period function.
Supplemental Controls
Compressor Lockout Relay (CLO) -- The CLO is available
as a factory-installed option or as a field--installed
accessory. Each compressor has a CLO. The CLO
compares the demand for compressor operation (via a
24-v input from Y at CLO terminal 2) to operation of the
compressor (determined via compressor current signal
input at the CLO’s current transformer loop); if the
compressor current signal is lost while the demand input
still exists, the CLO will trip open and prevent the
compressor from restarting until the CLO has been
manually reset. In the lockout condition, 24-v will be
available at terminal X. Reset is accomplished by
removing the input signal at terminal 2; open the
thermostat briefly or cycle the main power to the unit.
Phase Monitor Relay (PMR) -- The PMR protects the unit
in the event of a loss of a phase or a reversal of power line
phase in the three--phase unit power supply. In normal
operation, the relay K1 is energized (contact set closed)
and red LED indicator is on steady. If the PMR detects a
loss of a phase or a phase sequence reversal, the relay K1
is energized, its contact set is opened and unit operation is
stopped; red LED indicator will blink during lockout
condition. Reset of the PMR is automatic when all phases
are restored and phase sequence is correct. If no 24--v
control power is available to the PMR, the red LED will
be off. Smoke Detectors -- Factory--installed smoke
detectors are discussed in detail starting on page 17.
PremierLinkt Control
THERMOSTAT MODE — If the PremierLink controller
is configured for Thermostat mode (TSTAT), it will
control only to the thermostat inputs on J4. These inputs
can be overridden through CCN communication via the
CV_TSTAT points display table. When in this mode, the
fire safety shutdown (FSD) input cannot be used, so any
fire/life safety shutdown must be physically wired to
disable the 24 vac control circuit to the unit.
Indoor Fan — The indoor fan output will be energized
whenever there is 24 vac present on the G input. The
indoor fan will be turned on without any delay and the
economizer damper will open to its minimum position if
the unit has a damper connected to the controller. This
will also occur if the PremierLink controller has been
configured for electric heat or heat pump operation.
Cooling — For cooling operation, there must be 24 vac
present on G. When G is active, the PremierLink
controller will then determine if outdoor conditions are
suitable for economizer cooling when an economizer
damper is available. A valid OAT, SPT (CCN space
temperature) and SAT (supply air temperature) sensor
MUST be installed for proper economizer operation. It
recommended that an outdoor or differential enthalpy
sensor also be installed. If one is not present, then a
jumper is needed on the ENTH input on J4, which will
indicate that the enthalpy will always be low. Economizer
operation will be based only on outdoor air dry bulb
temperature. The conditions are suitable when: enthalpy is
low, OAT is less than OATL High Lockout for TSTAT,
and OAT is less than OATMAX, the high setpoint for free
cooling. The default for OATL is 65_F. The default for
OATMAX is 75_F.
When all of the above conditions are satisfied and all the
required sensors are installed, the PremierLink controller
will use the economizer for cooling. One of three different
control routines will be used depending on the
temperature of the outside air. The routines use a PID loop
to control the SAT to a supply air setpoint (SASP) based
on the error from setpoint (SASPSAT). The SASP is
determined by the routine.
If an economizer is not available or the conditions are not
met for the following economizer routines below, the
compressors 1 and 2 will be cycled based on Y1 and Y2
inputs respectively.
Any time the compressors are running, the PremierLink
controller will lock out the compressors if the SAT
becomes too low. These user configurable settings are
found in the SERVICE configuration table:
Compressor 1 Lockout at SAT < SATLO1 (50 to 65_F)
(default is 55_F)
Compressor 2 Lockout at SAT < SATLO2 (45 to 55_F)
(default is 50_F)
After a compressor is locked out, it may be started again
after a normal time--guard period and the supply--air
temperature has increased at least 8_F above the lockout
setpoint.
Routine No. 1: If the OAT ≤ DXLOCK (OAT DX lockout
temperature) and DX Cooling Lockout is enabled when
Y1 input is energized, the economizer will be modulated
to maintain SAT at the Supply Air Setpoint (SASP) =
SATLO1 + 3_F (Supply Air Low Temp lockout for
compressor 1). When Y2 is energized, the economizer
will be modulated to control to a lower SASP = SATLO2
+ 3_F (Supply Air Low Temp lockout for compressor no.
2). Mechanical cooling is locked out and will not be
energized.
48TC