Unit Operation; Cooling; Controller Set Above - Carrier TRANSICOLD 69NT20-274 Operation And Service

2.4 UNIT OPERATION

2.4.1 Cooling --- Controller Set Below --- 10_C (+14_F)
1. On Model 69NT40 units, the suction
solenoid valve (SSV) opens to increase the
refrigerant flow rate and cooling capacity at
---10_C (+14_F) unless SSV override is
activated.
2. In the frozen range the suction modulation
valve is 100% open.
3. The quench solenoid valve will not be
energized at this time as the suction
modulation valve position is greater than
40% open.
4. Some Models
expansion quench
Models have a solenoid quench valve refer
to Section 5.
5. Setting the
(+14_F) on units with two-speed motors
will place the motors in low speed (contactor
ES energizes).
When the return air temperature decreases to 0.2_C
(0.4_F) below set point, relays TC and TN de-energizes.
This results in de-energizing the compressor and
condenser fan motor. Also, the cool light is de-energized.
The evaporator fan motors continue to run to circulate
air throughout the container.
When the return air temperature increases to 0.2_C
(0.4_F) above set point, and providing a sufficient off
time period has elapsed, relays TC and TN energizes to
restart the compressor. Also, at this time, the condenser
fan motor starts and the cool light is illuminated.
2.4.2 Controller Set Above --- 10_C (+14_F)
Setting the
(+14_F) on units with two-speed motors
will place the motors in high speed (relay EF
energizes). (Contactor ES de-energizes)
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NOTES
have a thermostatic
valve. To see which
controller below ---10_C
NOTE
controller above ---10_C
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a. Cooling (See Figure 2-1.)
With decreasing supply air temperature and if the
supply air is above set point, the unit will be cooling with
the condenser fan motor, compressor motor and
evaporator fan motors energized. Also, at this time, the
cool light is illuminated.
When the air temperature decreases to a tolerance
above set point, relay TI energizes and the in-range light
is illuminated. (Refer to section 1.13.4. Code 29).
If the air temperature continues to fall, modulating
cooling starts at approximately 0.2_C (0.4_F) above set
point. The modulating valve will have a variable current
up to 1.30 amps at full modulation. At this time, it is
possible for the quench solenoid valve to energize before
the compressor shuts off as the valve energizes with a
minimum amp draw of 0.60. The quench solenoid valve
will de-energize if the modulation valve exceeds 60%.
Some Models
expansion quench
Models have a solenoid quench valve refer
to Section 5.
During this cooling mode, a running sum of the
temperature differential (supply air temperature --- set
point) is kept. When the supply air falls below set point,
the differential is negative. The longer supply air remains
below set point, the more negative the running sum
becomes.
When the supply air temperature decreases to 0.2_C
below set point and the running sum is less than ---250
degrees C seconds, relays TN and TC de-energize
shutting off the condenser fan and compressor motors.
Also, the cool light is de-energized.
The evaporator fan motors continue to run to
circulate air throughout the container. The in-range light
remains illuminated as long as the supply air is within a
tolerance of set point.
If the unit is in the holding mode (neither heating or
cooling) and the supply air temperature increases to
0.2_C (0.4_F) above set point, and providing a 6 minute
off time has elapsed, relay TC energizes to restart the
compressor. Also, at this time, the condenser fan motor
starts and the cool light is illuminated.
2-2
NOTE
have a thermostatic
valve. To see which