Carrier TRANSICOLD 69NT20-274, Операция и обслуживание

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1-12
Revised 8-6-93
1.10.2 Remote Monitoring Receptacle
When the remote monitor is connected to the
remote monitoring receptacle, the following remote
circuits are energized.
Circuit Function
Sockets B to A Energizes remote cool light
Sockets C to A Energizes remote defrost light
Sockets D to A Energizes remote in-range light
1.11 SUCTION SOLENOID VALVE
(Model 69NT40)
The suction solenoid valve, shown in Figure 1-3 is
controlled by the controller relay (TS).
a. Operation
If set point is below ---10
_
C (+14
_
F), and the suction
solenoid valve override is not activated, controller relay
(TS) closes to energize the suction solenoid valve (SSV).
Once opened, the refrigerant flow rate and unit cooling
capacity is increased.
If set point is above ---10
_
C (+14
_
F), and the suction
solenoid valve (SSV) is not activated, suction solenoid
valve opens during temperature pulldown period unless
current limiting restricts its use.
b. Suction Solenoid Override
This function restricts the opening of the suction
solenoid valve (SSV) under certain ambient and box
temperature conditions. If the primary return sensor
(RTS) fails (AL56), the suction solenoid valve will not
open unless the ambient temperature is less than 10
_
C
(50
_
F). If the ambient sensor fails (AL58), the suction
solenoid valve will not be allowed to open until the return
air temperature is less than 1.67
_
C (35
_
F). If both the
ambient and return air (RTS) sensors fail, the suction
solenoid valve will not be allowed to open until at least
one of the sensors is repaired.
1.12 FROST FORMATION ON COMPRESSOR
NOTE
Some Models have a thermostatic expansion
quench valve, so frost formation on compressor
is NOT APPLICABLE. To see which Models
have a solenoid quench valve refer to Section 5.
Frost may, in normal operation, form on the
compressor suction service valve and end bell. This is
caused by normal quench solenoid valve operation in
conjunction with the suction modulation valve.
Figure 1-6A shows the allowable frost limit pattern for
units operating with the controller set point above
---10
_
C (+14
_
F). This frost pattern is described below.
The temperature controller varies the amount of
current to the suction modulation valve coil (SMV) which
in turn increases or decreases the amount of restriction in
the suction line, so that the net cooling capacity of the
unit will match the cooling required to maintain the load
at set point.
When the suction modulation valve is approximately
40% closed (approximately 0.6 amps output to the
suction modulation valve coil from the temperature
controller), the temperature controller will energize the
quench solenoid valve. When the quench valve is opened,
a small amount of liquid refrigerant is metered through
an orifice (which acts as an expansion device) into the
suction line down stream of the suction modulation valve.
Because of low compressor suction pressures created by
the suction modulation valve, the liquid fed by the
quench valve flashes to a low temperature gas and,
therefore, the compressor may form frost or ice on the
end bell and top of the motor cavity adjacent to the
suction gas path of flow. This is not harmful to the
compressor, as the restrictor in the quench valve line
prevents excessive liquid from flowing into the
compressor.
With the controller set below ---10
_
C (+14
_
F) the
allowable compressor frost pattern limit is shown in
Figure 1-6B. The frost line will not normally extend
beyond the suction service valve as the quench valve will
not energize when operating with the controller set point
below ---10
_
C (+14
_
F).
If excessive frost is noticed on the compressor and
the suction modulation system is operating normally,
then the thermal expansion valve superheat setting
should be checked. Flooding by a thermal expansion
valve may cause oil to foam excessively. Normal quench
valve operation will not foam the oil significantly.
Adhesive-backed labels depicting allowable frost
patterns on compressors are available from Carrier
Transicold Replacement Component Group.
Figure A
Controller Set Above ---10
_
C (+14
_
F)
Figure B
Controller Set Below ---10
_
C (+14
_
F)
Figure 1-6. Frost Pattern on Compressors
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