Carrier TRANSICOLD 69NT20-274, Операция и обслуживание

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4-9
c. After unit is in operation, inspect for moisture in
system. (Refer to section 4.9.)
4.11 CHECKING OR REPLACING HIGH
PRESSURE SWITCH
4.11.1 Replacing High Pressure Switch
a. Store the refrigerant in an evacuated container
(Refer to Section 4.3.3). Frontseat both suction and
discharge service valves to isolate compressor.
b. Disconnect wiring from defective switch. The high
pressure switch is located on the center head and is
removed by turning counterclockwise. (See Figure 1-1.)
c. Install new cutout switch after verifying switch
settings. (Refer to section 4.11.2.)
d. Evacuate and dehydrate the compressor per section
4.5.1.o through 4.5.1.t.
4.11.2 Checking High Pressure Switch
WARNING
Do not use a nitrogen cylinder without a
pressure regulator. Do not use oxygen in or near
a refrigeration system as an explosion may
occur.
NOTE
The high pressure switch (HPS) is non-adjustable.
a. Remove switch as outlined in section 4.11.1.a
through c.
b. Connect ohmmeter or continuity light across switch
terminals. Ohm meter will indicate resistance and
continuity light will be illuminated if switch closed after
relieving compressor pressure.
c. Connect capillary to a cylinder of dry nitrogen. (See
Figure 4-14.)
1. Cylinder Valve
and Gauge
2. Pressure Regulator
3. Nitrogen Cylinder
4. Pressure Gauge
(0 to 36 kg/cm
@
=
0 to 400 psig)
5. Bleed-Off Valve
6. 1/4 inch Connection
1
2
3
4
5
6
Figure 4-14. Typical Setup for Testing High Pressure
Switch
d. Set nitrogen pressure regulator at 21 kg/cm
@
(300
psig) with bleed-off valve closed.
e. Close valve on cylinder and open bleed-off valve.
f. Open cylinder valve. Slowly close bleed-off valve to
increase pressure on switch. The switch will open at a
static pressure up to 21 kg/cm
@
(295 psig). If light is used,
light will go out and if ohmmeter is used, the meter will
indicate open.
g. Slowly open bleed-off valve to decrease the pressure.
The switch will close at 13 kg/cm
@
(190 psig).
4.12 SERVICING QUENCH SOLENOID VALVE (QV)
NOTE
This section is NOT APPLICABLE to
models having a thermostatic expansion
quench valve. To see which Models have a
solenoid quench valve refer to Section 5.
Replacing Solenoid Valve Coil
The coil may be removed without removing the
refrigerant.
Remove screw, lockwasher and coil. Disconnect
leads and remove coil. Verify new coil type, voltage and
frequency. (This information appears on the coil
housing.) Place new coil on valve stem and secure same.
4.13 REPLACING THE EVAPORATOR COIL
AND HEATER ASSEMBLY
The evaporator section, including the coil, should be
cleaned with fresh water or steam, preferably. Another
recommendation is to use Oakite 202 or similar cleaner
following manufacturer’s instructions.
The two drain pan hoses connected to the drain pan,
are routed behind the condenser fan motor and
compressor. The drain pan line(s) must be open to ensure
adequate drainage.
To Replace Evaporator Coil:
a. Store the refrigerant charge in an evacuated
container by attaching a line to the liquid line valve. (See
Figure 1-3 and refer to section 4.1)
b. With power OFF and power plug removed, remove
the screws securing the panel covering the evaporator
section (upper panel).
c. Disconnect the defrost heater wiring.
d. Disconnect the klixon from the coil. The defrost
termination thermostat (DTT) is located on the middle
coil support as shown in Figure 1-2.
e. Remove middle coil support.
f. Remove the mounting hardware from the coil.
g. Unsolder the two coil connections, one at the
distributor and the other at the coil header.
NOTE
It may be necessary to raise the fan deck to break
the solder connections (to raise coil).
h. After defective coil is removed from unit, remove
defrost heaters and install on replacement coil.
i.
Install coil assembly by reversing above steps.
j. Leak check connections per section 4.2. Evacuate
the unit per section 4.3 and add refrigerant charge per
section 4.4.2.
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