United Technologies Carrier Weathermaker 48A2, Controls, Start-Up, Operation, Service, And Troubleshooting

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The following information can be found under the Local
Display Mode Run Status

ECON . See Table 65.
Economizer Control Point Determination Logic — Once the
economizer is allowed to provide free cooling, the economizer
must determine exactly what setpoint it should try to maintain.
The setpoint 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 setpoints differently, based on the con-
trol 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 (see
below)
If Stage = 2 48.0 + economizer suction pressure reset (see
below)
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 setpoint, 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 93 psig. If this does not work, and if the suction pres-
sure drops below the trip point, then the control will further re-
set the control point 1 degree every 15 seconds up to a maxi-
mum 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 —
The building pressure
control sequence provides control of the pressure in the build-
ing through the modulating flow rate function of the modulat-
ing power exhaust option. This function also provides control
of the constant volume 2-stage power exhaust option.
BUILDING PRESSURE CONFIGURATION — The build-
ing pressure configurations are found at the local display under
Configuration

BP . See Table 66.
Building Pressure Config ( BP.CF ) — This configuration se-
lects the type of building pressure control.
•
BP.CF = 0, No building pressure control
• BP.CF = 1, constant volume two-stage power exhaust
based on economizer position
• BP.CF = 2, multiple stage building pressure control
based on a building pressure sensor
• BP.CF = 3, VFD building pressure control based on a
building pressure sensor
Building Pressure PID Run Rate ( BP.RT ) — This configura-
tion selects the run time of the PID algorithm. This configura-
tion is only active when BP.CF = 3. It is recommended that this
value not be changed without guidance from Service
Engineering.
Building Pressure Proportional Gain (
BP.P ) — This configura-
tion selects the proportional gain of the PID algorithm. This
configuration is only active when BP.CF = 3. It is recommend-
ed that this value not be changed without guidance from Service
Engineering.
Table 65 — Economizer Run Status Table
ITEM EXPANSION RANGE UNITS CCN POINT
WRITE STATUS
ECN.P Economizer Act.Curr.Pos. 0-100 % ECONOPOS
ECN.C Economizer Act.Cmd.Pos. 0-100 % ECONOCMD forcible
ACTV Economizer Active ? YES/NO ECACTIVE
DISA ECON DISABLING CONDITIONS
UNAV Econ Act. Unavailable? YES/NO ECONUNAV
R.EC.D Remote Econ. Disabled? YES/NO ECONDISA
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