035-17311-000 REV A (1200))
Unitary Products Group
29
COOLING OPERATION INSTRUCTIONS
COOLING SYSTEM PRELIMINARY OPERATION
NOTE: Prior to each cooling season, the crankcase heaters
must be energized at least 10 hours before the system is put
into operation.
TURN ON THE POWER TO THE UNIT
1.
Set the room thermostat setting to lower than the room
temperature.
2.
First stage compressors will energize after the built-in
time delay (five minutes)
3.
The second stage of the thermostat will energize second
stage compressor if needed.
POST START CHECK LIST
VERIFY PROPER SYSTEM PRESSURES FOR BOTH CIR-
CUITS
1.
Check the unit air flower (CFM). See “CHECKING AIR
QUANTITY” on page 25.
2.
Measure the temperature drop across the evaporator
coil.
3.
Check the voltage input.
4.
Measure the system Amperage draw across all legs of 3
phase power wires.
5.
Measure the condenser fan amps draw.
6.
Measure evaporator fan motor’s amp draw.
SHUT DOWN
1.
Set the thermostat to highest temperature setting.
2.
Turn off the electrical power to the unit.
SEQUENCE OF OPERATIONS
OVERVIEW
For the Predator
series of units, the thermostat makes a cir-
cuit between “R” and “Y1” for the first stage of cooling.
The call is passed to the unit control board (UCB), which then
determines whether the requested operation is available and,
if so, which components to energize.
For electric heat units, the UCB passes the call to the electric
heater. When the “W1” call is sensed, the indoor air blower is
energized following a specified heating delay.
If at any time a call for both heating and cooling are present,
the heating operation will be performed. If operating, the
cooling system is halted as with a completion of a call for
cooling. Heating always takes priority.
SAFETY CONTROLS
The Predator
unit control board monitors the following
inputs for each cooling system:
1.
A suction line freezestat to protect against low evapora-
tor temperatures due to a low airflow or a low return air
temperature, (opens at 26
±
5 °F and resets at 38
±
5
°F).
2.
A high-pressure switch to protect against excessive dis-
charge pressures due to a blocked condenser coil or a
condenser motor failure, (opens at 405
±
10 psig and
resets at 300
±
10 psig).
3.
A low-pressure switch to protect against loss of refriger-
ant charge, (opens at 7
±
3 psig and resets at 22
±
5
psig).
The above pressure switches are hard-soldered to the unit.
The refrigeration systems are independently monitored and
controlled. On any fault, only the associated system will be
effected by any safety/preventive action. The other refriger-
ant system will continue in operation unless it is effected by
the fault as well.
TABLE 29: MOTOR SHEAVE DATUM DIAMETERS
1VM50x7/8
(1-1/2, 2 & 3 HP Motor)
1VP56x1-1/8
(5 HP Motor)
Turns Open
Datum
Diameter
Turns Open
Datum
Diameter
0
4.4
1
5.3
1/2
4.3
1-1/2
5.2
1
4.2
2
5.1
1-1/2
4.1
2-1/2
5.0
2
4.0
3
4.9
2-1/2
3.9
3-1/2
4.8
3
3.8
4
4.7
3-1/2
3.7
4-1/2
4.6
4
3.6
5
4.5
4-1/2
3.5
5-1/2
4.4
5
3.4
6
4.3
After installation has been completed, energize the
crankcase heaters for at least four hours before
operating unit. After this initial warm-up, the com-
pressors should be given three false starts (ener-
gized just long enough to make a few revolutions)
with 5-7 minutes of delay between each start
before being put into full time service.
