Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 78

NOTE: If the user wishes to disable the enthalpy switch from
running concurrently, a field-supplied jumper must be installed
between TB201 terminals 3 and 4.
Enthalpy Switch
The state of the enthalpy switch can be viewed under In-
puts  GEN.I  ENTH. Enthalpy switches are installed as
standard on all N Series rooftops. When the switch reads
HIGH, free cooling will be disallowed.
The enthalpy switch has both a low and a high output. To use
this switch as designed, the control must be connected to the
"low" output. Additionally there is a "switch logic" setting for
the enthalpy switch
SW.LG  ENT.L. This setting must be configured to closed
(CLSE) to work properly when connected to the low output of
the enthalpy switch.
The enthalpy switch opens when the outdoor enthalpy is above
24 Btu/lb or dry bulb temperature is above 70°F and will close
when the outdoor enthalpy is below 23 Btu/lb or the dry bulb
temperature is below 69.5°F.
There are 2 jumpers under the cover of the enthalpy switch.
One jumper determines the mode of the enthalpy switch/re-
ceiver. The other is not used. For the enthalpy switch, the fac-
tory setting is M1 and should not need to be changed.
The enthalpy switch may also be field converted to a differen-
tial enthalpy switch by field installing an enthalpy sensor
(33CSENTSEN or HL39ZZ003). The enthalpy switch/receiver
remains installed in its factory location to sense outdoor air en-
thalpy. The additional enthalpy sensor is mounted in the return
air stream to measure return air enthalpy. The enthalpy control
jumper must be changed from M1 to M2 for differential
enthalpy control. For the return air enthalpy sensor, a "two-
wire" sensor, connect power to the Vin input and signal to the
4 to 20 mA loop input.
It should be noted that there is another way to accomplish dif-
ferential enthalpy control when both an outdoor and return air
relative humidity sensor are present. See section on Economiz-
er Changeover Select for further information.
Economizer Changeover Select
The control is capable of performing any one of the following
changeover types in addition to both the dry bulb lockout and
the discrete switch input:
E.SEL = 0 none
E.SEL = 1 Differential Dry Bulb Changeover
E.SEL = 2 Outdoor Enthalpy Changeover
E.SEL = 3 Differential Enthalpy Changeover
Differential Dry Bulb Changeover
As both return air and outside air temperature sensors are in-
stalled as standard on these units, the user may select this op-
tion, E.SEL = 1, to perform a qualification of return and out-
side air in the enabling/disabling of free cooling. If this option
is selected and outside-air temperature is greater than return-air
temperature, free cooling will not be allowed.
Outdoor Enthalpy Changeover
This option should be used in climates with higher humidity
conditions. Unlike most control systems that use an enthalpy
switch or enthalpy sensor, the N Series units can use the stan-
dard installed outdoor dry bulb sensor and an accessory rela-
tive humidity sensor to calculate the enthalpy of the air.
Setting E.SEL = 2 requires that the user configure OA.E.C, the
"Outdoor Enthalpy Changeover Select" configuration item, in-
stall an outdoor relative humidity sensor, and make sure a con-
trol expansion module board (CEM) is present. Once the sen-
sor and board are installed, all the user need do is to enable
ORH.S, the outdoor relative humidity sensor configuration op-
tion. This, in turn, will enable the CEM board to be read, if it is
not so already, automatically.
under Configuration  IAQ 
NOTE: If the user wishes to disable the enthalpy switch from
running concurrently, a field-supplied jumper must be installed
between TB201 terminals 3 and 4.
Differential Enthalpy Changeover
This option compares the outdoor air enthalpy to the return air en-
thalpy and favors the airstream with the lowest enthalpy. This op-
tion should be used in climates with high humidity conditions.
This option uses both humidity sensors and dry bulb sensors to
calculate the enthalpy of the outdoor and return air. An accessory
outdoor air humidity sensor (ORH.S) and return air humidity sen-
sor (RRH.S) are used. The outdoor air relative humidity sensor
configuration (ORH.S) and return air humidity sensor configura-
tion (Configuration  SENS  RRH.S) must be enabled.
NOTE: If the user wishes to disable the enthalpy switch from
running concurrently, a field-supplied jumper must be installed
between TB201 terminals 3 and 4.
Outdoor Dewpoint Limit Check
If an outdoor relative humidity sensor is installed, the control is
able to calculate the outdoor air dew point temperature and will
compare this temperature against the outside air dew point
temperature limit configuration (O.DEW).
If the outdoor air dew point temperature is greater than
O.DEW, "free cooling" will not be allowed.
Custom Psychometric Curves
See Fig. 11 for an example of a custom curve constructed on a
psychometric chart.
Configuring the Economizer to Communicate Via Actuator
"Serial Number"
Every actuator used in the N Series control system has its own
unique serial number. The rooftop control uses this serial num-
ber to communicate with the actuator over the local equipment
network (LEN). These serial numbers are programmed at the
factory and should not need changing. Should field replace-
ment of an actuator become necessary, it will be required to
configure the serial numbers of the new actuator. 6 individual
numbers make up this serial number and these can be pro-
grammed to match the serial number of the actuator in its
"Economizer Actuator Configs" group, ACT.C. (SN.1.1,
SN.1.2, SN.1.3, SN.1.4, SN.1.5, SN.2.1, SN.2.2, SN.2.3,
SN.2.4, SN.2.5, SN.3.1, SN.3.2, SN.3.3, SN.3.4, SN.3.5).
NOTE: The serial numbers for all "LEN" actuators can be
found inside the control doors of the unit as well as on the actu-
ator itself. If an actuator is replaced in the field, it is a good
idea to remove the additional peel-off serial number sticker on
the actuator and cover up the old one inside the control doors.
Control Angle Alarm Configuration
The economizer actuator learns what its end stops are through
a calibration at the factory. Field-installed actuators may be
calibrated in the Service Test mode. When an actuator learns its
end stops through calibration, internally it remembers what its
"control angle" is. From that moment on, the actuator will re-
solve this control angle and express its operation in a percent
(%) of this "learned range."
If the economizer has not learned a "sufficient" or "large
enough" control angle during calibration, the economizer
damper will be unable to control ventilation and free cooling,
For this reason the economizer actuator used in the N Series
control system has a configurable "control angle" alarm low
limit in its "Economizer Actuator Configs" group, ACT.C.
(C.A.L1, C.A.L2, C.A.L3). If the control angle learned through
calibration is less than C.A.L1, C.A.L2, or C.A.L3, an alert will
occur and the actuator will not function.
NOTE: This configuration does not typically need adjustment.
It is configurable for the small number of jobs which may re-
quire a custom solution or workaround.
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