Carrier WEATHERMASTER 48Z030, Operation And Service Manual

Page: 69 / 180

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The economizer’s reported and commanded positions
are also viewable, as well as outside air temperature, relative
humidity, enthalpy and dew point temperature.
The following information can be found under the Local
Display Mode Run Status
→
ECON . See Table 57.
Economizer Control Point Determination Logic — Once the
economizer is allowed to provide free cooling, the economizer
must determine exactly what set point it should try to maintain.
The set point the economizer attempts to maintain when “free
cooling” is located at Run Status
→
VIEW
→
EC.C.P . This is
the economizer control point.
The control selects set points differently, based on the
control type of the unit. This control type can be found at
Configuration
→
UNIT
→
C.TYP . There are 6 types of control.
C.TYP = 1 VAV-RAT
C.TYP = 2 VAV-SPT
C.TYP = 3 TSTAT Multi-Staging
C.TYP = 4 TSTAT 2 Stage
C.TYP = 5 SPT Multi-Staging
C.TYP = 6 SPT 2 Stage
If the economizer is not allowed to do free cooling, then
EC.C.P = 0.
If the economizer is allowed to do free cooling and the
Unoccupied Free Cooling Mode is ON, then EC.C.P =
Setpoints
→
SASP + Inputs
→
RSET
→
SA.S.R .
If the economizer is allowed to do free cooling and the
Dehumidification mode is ON, then EC.C.P = the Cooling
Control Point ( Run Status
→
VIEW
→
CL.C.P ).
If the C.TYP is either 4 or 6, and the unit is in a cool mode,
then:
If Stage = 0
EC.C.P = the Cooling Control Point ( Run
Status
→
VIEW
→
CL.C.P )
If Stage = 1 53.0 + economizer suction pressure reset
If Stage = 2 48.0 + economizer suction pressure reset
NOTE: To check the current cooling stage go to Run Status
→
Cool
→
CUR.S .
If the C.TYP is either 1,2,3 or 5, and the unit is in a cool
mode, then EC.C.P = the Cooling Control Point ( Run Status
→
VIEW
→
CL.C.P ).
Economizer Suction Pressure Reset for Two-Stage
Cooling — If the unit’s control type is set to either 2-stage ther-
mostat or 2-stage space temperature control, then there is no
cooling control point. Stages 1 and 2 are brought on based on
demand, irrespective of the evaporator discharge temperature.
In this case, the economizer monitors suction pressure and
resets the economizer control point accordingly in order to
protect the unit from freezing. For those conditions when the
economizer opens up fully but is not able to make set point, and
then a compressor comes on, it is conceivable that the coil
might freeze. This can be indirectly monitored by checking suc-
tion pressure. Rather than fail a circuit, the control will attempt
to protect the unit by resetting the economizer control point
until the suction pressure rises out of freezing conditions.
If either circuit’s suction pressure drops to within 5 psig
of the low suction pressure trip point, the control will start
adding reset to the economizer control point if it is active. It
will be possible to reset the control point upwards, 10 degrees
(2 degrees per psig), between the low suction pressure trip
point of 48 psig and 5 psig above it. If this does not work, and if
the suction pressure drops below the trip point, then the control
will further reset the control point 1 degree every 15 seconds
up to a maximum of 10 degrees. The resulting effect will be to
warm up the mixed air entering the evaporator, thereby raising
the suction pressure.
Building Pressure Control —
This control sequence
provides control of the building pressure through the modulat-
ing flow rate functions of one of the modulating power exhaust
options or through management of the return fan option. This
function also provides control of the constant volume 2-stage
power exhaust option. See below for available power exhaust
options for each unit model.
LEGEND
Table 57 — Economizer Run Status Table
UNIT
CONSTANT
VOLUME
2-STAGE
MODULATING
POWER
EXHAUST
S.O.
VFD*
HIGH
CAPACITY
POWER
EXHAUST†
RETURN/
EXHAUST†
48ZG, 50ZG,Z2 X X S.O. NA NA
48ZN, 50ZN,Z3 NA X S.O. NA NA
48ZT,ZW
50ZT,ZW,ZX,ZZ
NA NA NA STD NA
48Z6,Z8
50Z6,Z7,Z8,Z9
NA NA NA NA STD
X — Available as Factory Option
S.O. — Available as Special Order
NA — Not Available on this Unit
STD — Standard Feature on this Unit
ITEM EXPANSION RANGE UNITS CCN POINT WRITE STATUS
ECN.P Economizer Act.Curr.Pos. 0-100 % ECONOPOS
EC2.P Economzr 2 Act.Curr.Pos. 0-100 % ECON2POS
ECN.C Economizer Act.Cmd.Pos. 0-100 % ECONOCMD forcible
ACTV Economizer Active ? YES/NO ECACTIVE
DISA ECON DISABLING CONDITIONS
UNV.1 Econ Act. Unavailable? YES/NO ECONUNAV
UNV.2 Econ2 Act. Unavailable? YES/NO ECN2UNAV
ENTH Enth. Switch Read High ? YES/NO ENTH
DBC DBC - OAT Lockout? YES/NO DBC_STAT
DEW DEW - OA Dewpt.Lockout? YES/NO DEW_STAT
DDBC DDBD- OAT > RAT Lockout? YES/NO DDBCSTAT
OAEC OAEC- OA Enth Lockout? YES/NO OAECSTAT
DEC DEC - Diff.Enth.Lockout? YES/NO DEC_STAT
EDT EDT Sensor Bad? YES/NO EDT_STAT
OAT OAT Sensor Bad ? YES/NO OAT_STAT
FORC Economizer Forced ? YES/NO ECONFORC
SFON Supply Fan Not On 30s ? YES/NO SFONSTAT
CLOF Cool Mode Not In Effect? YES/NO COOL_OFF
OAQL OAQ Lockout in Effect ? YES/NO OAQLOCKD
HELD Econ Recovery Hold Off? YES/NO ECONHELD
DH.DS Dehumid. Disabled Econ.? YES/NO DHDISABL
O.AIR OUTSIDE AIR INFORMATION
OAT Outside Air Temperature dF OAT forcible
OA.RH Outside Air Rel. Humidity % OARH forcible
OA.E Outside Air Enthalpy OAE
OA.D.T Outside Air Dewpoint Temp dF OADEWTMP
*Single VFD controlling both fan
motors.
†Single VFD controlling one fan
motor and staging of the second
fan motor.