Specifications

530.25-N1
START-UP
CRANKCASE HEATERS
- It is
important that the crankcase heaters be energved 8 hours
before starting the compressors.To energize the crankcase
heaters, the room thermostat or status panel system switch must
be open to prevent the compressor from starting. If a disconnect
switch is installed outside the unit, turn it to “ON”. The non-
fused disconnect (optional) located in the unit’s main supply
panel must also be turned ‘ON”.
7.
8.
CAUTION: Do not attempt to start the compressorswithout
at least 8 hours ofcrankcase heat or compressor
damagewill occur.
9.
SAFETY AND SERVICE FEATURES
The control circuit includes the following safety features:
1. The supply air blower motor is protected with manual re-
set starter overload protectors.
2. The condenser fan motors have inherent protection.with
automatic reset.
3. The primary windingof transformer IT is protected by
fuse 12FU. The secondary windingand the 115volt con-
trol circuit are protected by fuse 13FU.
4. All safety controls in the 115
volt circuit havethe “return”
or “common’
side of the 1T transformer grounded. Fuse
13FUwill “BLOW”whenever a dangerous condition occurs.
The un]t casing is also grounded.
5. The wlr]ngto each compressor motor, each condenser fan
motor and the supply air blower motor are individually
fused according to the National Electrical Standards.
6. The compressor(s) are protected by a 100watt immersion
type crankcase heater(s). Heater(s) are energized whenever
power ISsupplied to the umt. When the compressor(s) are
energized, the heater(s) are turned off.
CAUTION: Do not attempt to start the compressors without
at least 8 hours of crankcaseheat or compressor
damage will occur.
CES
10.
11.
I2.
13.
14,
Each refrigeration system has a low pressurecutout ( ILP
for system No. I and 2LP
for systemNo. 2) to shut down
the compressor duc to lossof refrigerant charge or a build
up of frozen condensate on the compressor before the suc-
tion valveand are set to open when the suction pressure
drops to 7 psig.These controls WIIIautomatically reset
when the suction pressuresrise to 22 psig.The opening of
the low pressure cutouts WI]]activate the lockout circuit.
Highpressure
cutouts ( 1HPfor system No. I and 2HP for
system No. 2) are located in each system on the compressor
before the discharge valve.Should a system discharge pres-
sure exceed 398 psig, the control will open and de-energl~e
the compressor, The pressurecutout will close when the
dischargepressure drops to 310 psig.The opening of the
high pressurecutout will activate the lockout circuit. The
high pressure cutouts may open due to a dirty or restricted
condenser coil, loss of air flow or too high an ambient air
temperature.
The lockout circuits mentioned above WIIInot be energized
during normal operation because they have a high resistance.
The flow of electricity will normally follow the path of
least resistance through the compressor contractors IM and
2M. lf, however, a low or high pressure cutout opens, the
lockout relay IORor 11R WIIIbe energized. Since the volt-
age across 10R or 11R WI]]exceed 10OV,the voltage across
1Mor 2Mwill be too low to pull in the contractors.The nor-
mally closed contacts of 10Ror 11R will open the circuit m
series with the low or high pressure cutout. Whenthese con-
tacts automatically close, the lockout circuit can be reset by
interrupting the control circuit at the room thermostat.
Two advantagesare gained by this circuit:
a. Prevents rapid cyclingof the compressors which can be
damaging.
b. The alternate use of manual reset cutoffs avoids the pro-
blem above but may require an expensive servicecL1to
reset these controls.
Freezestat 3TH sensesthe suction temperature of the No. 1
system and will shut down compressor(s) when this tem-
perature drops to 32”F. It will reset automatically at 37°F.
The supply air flow must be proven by vacuum switch 5LP.
In the event the belts on the supply air motor break or the
supply air motor should be de-energizedby its overload pro-
tectors, 5LP wdl open and interrupt the cooling, heating
and economizer control circuits. This assuresthat the various
modes of operation do not continue without proper air flow.
The compressor motor protector(s), 1MP,2MPwill interrupt
the compressor control circuit when sensingan overload con-
dition. Alsoan anti-recycle timer is part of this device to pre-
vent the compressor from rapid cycling. The compressor will
stay off for five minutes. It also monitors the voltage of the
120volt control circuit and will shut down the compressor if
the voltage drops below 85~ 4.5 volts.
Oil pressurecontrol switches are installed In the compressor
circuits. These assure that adequate oil pressure ISpresent to
lubricate the movingparts of the compressor. If pressure IS
not adequate. the switch opens shutting down the compressor.
It is manually reset.
Whenthe pumpdown accessory, Model 2PD04700101, is ]n-
stalled, the compressor will continue to operate through con-
tact i 2TR-2after the room thermostat or controller 1ssatisfied.
23