CHECKING THE SYSTEM PRIOR TO
INITIAL START UP
With the system piping and electrical wiring completed, the unit
is ready to have electrical power applied. Before applying
power, however, the following checks should be made:
1. Compressor shipping brackets have been removed and
rubber isolators installed.
2. The Return Liquid Temperature Contron (TC) has been
adjusted to the desired Return Liquid Temperature and
Between Stage Differential.
3. The Freeze Control thermostat (FC) has been set to the
proper setting. (Factory setting is 36
°
F.)
4. Fan blades rotate freely.
5. Compressor crankcase oil level shows 1/3 to 1/2 in sight
glass.
6. Suction, discharge and liquid line king valves, located in the
compressor section, are open. There are two systems in
these units and each system employs one of these valves.
CAUTION: Suction, discharge and liquid line valves are
shipped closed.
7. The power supply voltage is the same as the unit name-
plateu voltage.
8. Proper fuses are in main disconnect power circuits.
APPLYING POWER TO THE UNIT
CAUTION With the preceding steps completed, make sure
the DAY/NIGHT switch is in the NIGHT or UNOC-
CUPIED position or the unit will start immediately
and compressor damage may occur.
1. The main power disconnect switch may now be turned ON.
CAUTION: Check to insure that the compressor crankcase
heater is energized. Allow at least 24 hours
warm-up to allow all liquid refrigerant to be
driven from the compressors. After warm-up,
the crankcase should be warm to the touch.
2. Start the chilled water circulating pump. Assure that the flow
rate is approximately correct by checking the water pres-
sure drop across the cooler with the data shown in Table 5.
3. Check that the liquid freeze prevention thermostat (FC)
does not need to be reset. It may have tripped if the unit
was exposed to low outdoor temperatures during shipment.
4. Turn the DAY/NIGHT switch to the DAY or OCCUPIED
position. If the water flow switch is closed, the unit will start
after the required time delays built into the control circuit,
provided the return liquid temperature is warm and the
temperature control (TC) is calling for cooling.
5. Allow the unit to operate, but be ready to stop the unit should
any unusual noise or other adverse condition develop.
NOTE: Opening the DAY/NIGHT switch will only shut the
unit off after completion of the pumpdown cycle.
Turning OFF the main power supply will stop the
unit immediately.
6. To determine if the unit is operating properly, the refrigerant
subcooling and superheat should be checked.
SEQUENCE OF OPERATION
NOTE:
The contact opening and closing times for 50 HZ
units are 5/6 of those listed for 60 HZ units.
System start-up and staging is controlled by the TC which is
energized through the day/night switch, optional field installed
pump aux. contact, FC and WFS. The FC opens below 36
°
F
leaving water temperature and closes above 42
°
F with manual
reset. The WFS closes at water flow rates above 55 GPM. The
TC is a solid state thermostat which maintains the desired
chilled (supply) liquid temperature by sensing and regulating
the return liquid temperature (see the ELECTRICAL CON-
TROLS section). It employs an encapsulated thermistor lo-
cated in a well in the return liquid line.
NOTE: The timing intervals described in the following proce-
dure are nominal. Some variations will naturally occur
due to differences in individual components, ambient
temperature, or line/control voltage.
COMPRESSOR NO. 1 OPERATION
When the first stage of the TC calls for cooling.:
1. TC-1 closes and energizes relay 16R. 16R-1 will energize
compressor protector module MP, and after a 2 minute time
delay 1MP contacts will close. Contact 16R-3 closes
energizing contactors 1M, 5M, relays 1R, 20R, and timer
1TR. 16R-2 energizes liquid line solenoid valve 1LLS, and
liquid refrigerant will flow to the expansion valve.
2. Relay 1R contacts close, with 1R-1 and 1R-2 closing in
parallel with contacts 16R-1 and 16R-3 respectively main-
taining operation during the pumpdown cycle.
3. Contactor 1M energizes compressor #1, and contactor 5M
energizes the condenser fans #1, #2 and #3. Contact 20R
opens to de-energize compressor crankcase heater 1CCH
while the compressor runs.
4. After 2 minutes, low pressure bypass timer 1TR-1 opens.
If the compressor suction pressure remains abnormally low
after initial start-up, the compressor circuit will lock out as
described in the HIGH / LOW PRESSURE LOCKOUT
section.
When the second stage of the TC calls for cooling:
1. Contacts TC-3 will close to energize relay 4R, and con-
denser fan No. 2 will start up, providing the temperature of
the outdoor air is above the 45
°
F set point of thermostat
2TH.
2. Contact TC-4 will open to de-energize compressor solenoid
valve 2SOL, and the 20 ton compressor will operate at full
capacity.
OPERATION
570.05-N4Y
8
Unitary Products Group