1-10
Revised 8-6-93
Table 1-3. Safety and Protective Devices
UNSAFE CONDITIONS
SAFETY DEVICES
DEVICE SETTING
1. Excessive current draw
1. Circuit Breaker (CB-1) ---
Manual Reset
1. Trips at 24 amps
(460 vac 69NT20)
1. Trips at 29 amps
(460 vac 69NT40)
1. Circuit Breaker (CB-2) ---
Manual Reset
1. Trips at 50 amps
(230 vac)
2. Excessive current draw on control circuit
2. Fuse (F)
2. Opens at 6 amps
3. Excessive condenser fan motor
winding temperature
3. Internal Protection (IP-CM) ---
Automatic Reset
3. N/A
4. Excessive compressor motor winding
temperature
4. Internal Protector (IP-CP) ---
Automatic Reset
4. N/A
5. Excessive evaporator fan motor(s)
winding temperature
5. Internal Protector(s) (IP-EM) ---
Automatic Reset
5. N/A
6. Abnormally low refrigerant temperature
6. Pressure Relief Valve ---
Low Side
6. Opens at 18.63 kg/cm
@
(265 psig)
7. Abnormally high refrigerant temperature
7. Pressure Relief Valve ---
High Side
7. Refer to paragraph 1.3.k
8. Abnormally high discharge pressure
8. High Pressure Switch
8. Refer to paragraph 1.3.i
9. Solid state circuitry high voltage surge 9. Fuse (F3A)
9. Opens at 5 amps
10. Excessive power transformer winding
temperature
10. Internal Protector (IP-Trans) ---
Automatic Reset
10. Opens at 178
¦
5
_
C
(350
¦
10
_
F)
Closes at 150
¦
7
_
C
(300
¦
12
_
F)
1.7 SAFETY AND PROTECTIVE DEVICES
System components are protected from damage by
safety and protective devices listed in Table 1-3. These
devices monitor the system operating conditions and
open a set of electrical contacts when an unsafe condition
occurs.
Open safety switch contacts of one or more of the
following devices IP-CM, IP-CP, HPS, or IP-Trans (Auto)
will shut down the compressor and condenser fan motor.
The entire refrigeration system will shut down if one
of the following safety devices open: (a) Circuit
Breaker(s) or; (b) Fuse (6A) or; (c) Evaporator Fan
Motor Internal Protector(s) --- (IP-EM).
1.8 REFRIGERATION CIRCUIT
Starting at the compressor, the suction gas is
compressed to a higher temperature and pressure.
When operating with the
air-cooled condenser,
the
gas flows through the discharge service valve into the
air-cooled condenser. Air flowing across the coil fins and
tubes cools the gas to saturation temperature. By
removing latent heat, the gas condenses to a hot liquid
and then flows to the water-cooled condenser/receiver
which stores the additional charge necessary for low
temperature operation.
When operating with the
water-cooled condenser,
the
hot gas flows through the air-cooled condenser and into
the water-cooled condenser. The heat flows from the hot
gas into the condenser coolant thus cooling the
compressed gas and changing the state of refrigerant
from a gas to a liquid.
From the condenser/receiver, the liquid refrigerant
flows by a pressure relief valve which opens if the
refrigerant pressure is abnormally high.
The liquid refrigerant continues through a liquid line
shutoff valve, filter-drier (which keeps refrigerant clean
and dry), a moisture-liquid indicator and then to the
thermostatic expansion valve. As the liquid refrigerant
passes through the orifice of the expansion valve some of
it vaporizes into a gas (flash gas). Heat is absorbed from
the evaporator air by the balance of the liquid causing it
to vaporize in the evaporator coil. The vapor then flows
through the modulating solenoid valve to the
compressor.
The thermostatic expansion valve bulb on the suction
line near the evaporator coil outlet, controls the valve,
maintaining a relatively constant superheat at the coil
outlet regardless of load conditions except at abnormally
high container temperatures such as during pulldown
(valve at maximum operating pressure condition).
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