WATER COOLER FREEZE PREVENTION
Off-cycle cooler freeze protection is provided when liquid is not
flowing to the cooler and the outdoor ambient is low. Under
these conditions, the water flow switch contact WFS is relaxed,
and the cooler heater HTR and 15R relay are energized
through the 7TH thermostat which closes below 36
°
F. The
cooler heater is a pad type heater fixed to the cooler under the
insulation. The 15R contact closes to energize field installed
water line heaters. The power for these heaters comes from a
separate disconnect switch. See Figure 4.
COMPRESSOR MOTOR PROTECTION SYSTEM
The solid state motor protection system consists of a solid state
overload protector module and three sensors embedded in the
compressor motor windings. The sensors are connected to the
solid state overload protector module 1MP and 2 MP. Refer to
the wiring label on the inside of the compressor terminal box
cover. This system provides 2 minute off-time delay before the
compressor can restart.
CONDENSER FAN MOTOR CONTROL
Condenser fans motors cycle with the temperature of the
outdoor air to maintain sufficient head pressure for stable
operation over a wide range of conditions. One condenser fan
motor per compressor can operate at a reduced speed without
overheating. When the discharge pressure drops below 180
psig, the speed of this motor drops from 1075 to 450 RPM.
When the discharge pressure rises above 222 psig, the motor
will return to 1075 RPM. This speed reduction is accomplished
by using a choke coil to reduce the voltage to the motor. A 10
second time delay relay is included in the control circuit so
these motors will always start at high speed. Refer to Figure 6.
EXAMPLE W1LC420:
NO. 1 (20 TON) SYSTEM - Under 65
°
F, the #1 condenser fan
will shut off. Under 45
°
F, the #2 condenser fan will shut off. At
1/2 capacity, the #2 condenser fan will shut off. When the
discharge pressure drops below 180 psig, high pressure con-
trol 2HP will close to energize relay 3R. When contact 3R-1
opens and contact 3R-2 closes, condenser fan #3 will be
powered through choke coil 1CH and its speed will drop to 450
RPM. Timer 3TR will remain open for 10 seconds after unit
start-up so the condenser fan #3 will always start at high speed.
NO. 2 (20 TON) SYSTEM - Under 65
°
F, the #4 condenser fan
will shut off. Under 45
°
F, the #5 condenser fan will shut off. At
1/2 capacity, the #5 condenser fan will shut off. When the
discharge pressure drops below 180 psig, high pressure con-
trol 4HP will close to energize relay 10R. When contact 10R-1
opens and contact 10R-2 closes, condenser fan #6 will be
powered through choke coil 2CH and its speed will drop to 450
RPM. Timer 7TR will remain open for 10 seconds after unit
start-up so the condenser fan #6 will always start at high speed.
EXAMPLE W1LC530:
NO. 1 (20 TON) SYSTEM - Under 65
°
F, the #1 condenser fan
will shut off. Under 45
°
F, the #2 condenser fan will shut off. At
1/2 capacity, the #2 condenser fan will shut off. When the
discharge pressure drops below 180 psig, high pressure con-
trol 2HP close to energize relay 3R. When contact 3R-1 opens
and contact 3R-2 closes, condenser fan #3 will be powered
through choke coil 1CH and its speed will drop to 450 RPM.
Timer 3TR will remain open for 10 seconds after unit start-up
so the condenser fan #3 will always start at high speed.
NO. 2 (30 TON) SYSTEM - Under 65
°
F, the #4 condenser fan
will shut off. Under 45
°
F, the #5 condenser fan will shut off. At
1/3 capacity, the #5 condenser fan will shut off and the #6
condenser fan will shut off if the ambient temperature is below
75
°
F. When the discharge pressure drops below 180 psig, high
pressure control 4HP will close to energize relay 10R. When
contact 10R-1 opens and contact 10R-2 closes, condenser fan
#7 will be powered through choke coil 2CH and its speed will
drop to 450 RPM. Timer 7TR will remain open for 10 seconds
after unit start-up so the condenser fan #7 will always start at
high speed.
FIG. 6 - CONDENSER FANS ORIENTATION
570.05-N4Y
10
Unitary Products Group