Specifications

530.25-N1
SOLID STATE CONTROLS
A Honeywell W973 solid state Ioglc panel controls the econ-
crmi~,ermotor and stagesof coohng and heating in response
- to a signal from a dual set point thermostat located in the
controlled space or a dual set point transmitter with a remote
sensor located in the controlled space. To maintain stable
space temperatures, the ]oglc panel balances the space thermo-
stat demand s]gnal against the system output. System output
is measured by a temperature sensor located on the discharge
alr duct. The comblned demand and output signals determine
the
economl/er position irnd the number of heat]ng or cool-
ing stagesenerg]zed. The discharge sensor also provides a pos-
itive modulating low limit signal to the logic panel, insuring
that the economizer will modulate closed if discharge air gets
too cold.
On a power failure, all stagesgo off and the damper motor
goesto the OYoutside air pos]t]on. Whenpower is restored,
the required stages sequence on w]tb a time delay between
stages.
The operation of these umts cun be dwided into four
systems.
1. Economizer System (optional)
2. I Ieat ing System (optional)
3. Cooling System
4. Exhaust Air (optional)
-
ECONOMIZER SYSTEM
The E.conomiyer System consists of:
Outdoor and return air dampers.
Damper Actuator (Spring Return).
Enthalpy Control - 5TH.
Minimum outdoor alr adjustor (potent mneter) - 2RH.
The Economizer system provides the first stage of cooling
whenever the outdoor air is cool and dry enough to satisfy
the internal cooling demand. The outdoor and the return
au dampers are mechanically linked and are mounted by
the spring return damper actuator. As the outdoor au dam-
pers are opened by the damper actuator the re@rrnalr dam-
pers are closed.
When the enthalpy cent rot (5TH) sensesoutdoor alr temp-
eratures per Table 5, the outdoor air dampers close to then
minimum position. The minimum position of the outdoor
air dampers is determined by the set point of the minimum
outdoor air adjustor ( 2RH). The minimum outdoor air ad-
juster is factory mounted in the top of the damper motor.
The enthalpy control (5TH) is factory set. It sensesboth
temperature and humidity and varies its setting so as to
limit the introduction of outdoor air. As noted in Table 5,
L
the control will not allow outdoor air to enter the unit
during high hum]dity conditions except at a lower outdoor
temperature. During dry conditions, air is introduced at a
higher ambient.
CES
The outdoor and return alr dampers are controlled by the
logic panel. The discharge sensoracts as a modulating low
limit which sensesthe temperature of the air leaving [he
evaporator coil. If at any time during the cooilng cycle the
dls.chargeair temperature drops to 62” F, the econormzer
motor starts to modulate closed. The economizer motor
will be at minimum position when discharge air tempera-
ture is 50° F,
If the economizer cannot satisfy the space demand for
cooling, mechanical cooling stagesare energj?ed as needed.
DAMPER LINKAGE ADJUSTMENT
After power has been supphed to the unit. the outside and
return air dampers should be checked to make sure they
operate freely and close tightly. It may be necessary to re-
adjust the linkage between the damper motor and the blades
due to loosening in shipment.
Readjust linkage as follows:
1
‘-J
.
3
4
Turn the minimum outside air adjustor to the 100% out-
side air position. Al] return air damper blades should be
fully closed. Be sure that the spring-return damper act-
uator has completed its stroke (stopped running). If not,
loosen the drive
rod bolt and let the damper motor drive
the crankarm until the motor stops running. Retighten
the drive
rod bolt to secure the drive rod.
Turn the minimum outside alr adjustor to the 0% outside
air position. All outside air damper blades should be fully
closed. The linkage connecting the outside air and the re-
turn air dampers must move freely.
Return the minimum outside air adjustor to the 100%
outside air position and check for complete freedom of
linkage movement as the return air dampers close.
Set the minimum outside air adjustor for the minimum
ventilation requirement of the job.
HEATING SYSTEM
Two different types of heat are offered as factory-mounted
options. Refer to the appropriate instruction for informa-
tion on the heating system.
Gas-Fired Heating Option
– Form 530.25 -NI.1
Electric Heating Option
– Form 530.25 -N1.9
COOLING SYSTEM
These units have nominal cooling capacities of 25, 30 and
40
tons. The DSC300and DSC360 units haveone semi-her-
metic compressor.
Two cooling stages are accomplished by
unloading the compressor.The DSC480 unit has two semi-
hermetic compressors.Two coolingstages are accomplished
by cyclingthe individual compressors.
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