2-3
point. The modulating valve will have a variable current
up to 1.30 amps at full modulation.
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, and the 15 minute override is met.
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 3 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.
b. Heating (See Figure 2-2.)
The unit
will only heat
when the controller set point is
above ---10
_
C (+14
_
F) or ---5
_
C (+23
_
F) optionally as
relay TH is electronically locked out to prevent heating
when the controller set point is
below
---10
_
C (+14
_
F) or
---5
_
C (+23
_
F) optionally.
If the air temperature decreases 0.5
_
C (0.9
_
F) below
controller set point, TH closes and the system enters the
heating mode which is designed to raise the container air
temperature. When TH closes, power flows through TH
contacts and the heat termination thermostat to energize
the heat relay (HR). This in turn energizes the heaters
and heat light. The evaporator fans continue to run to
circulate air throughout the container.
As the supply air decreases to the in-range tolerance
below set point, relay TI and the in-range light
de-energize (after 15 minutes time delay) and will remain
de-energized until the supply air increases to a tolerance
below set point. (Refer to section 1.12.5, Code 30)
When the temperature rises to 0.2
_
C (0.4
_
F) below
set point, TH opens (heating off) and the system again
enters the holding zone. The compressor and condenser
fan motor are not running as contactors C and CF remain
de-energized. The evaporator fans continue to run to
circulate air throughout the container.
A safety heater termination thermostat (HTT)
attached to an evaporator coil support, set to open at
54.5
_
C (130
_
F), will open the heating circuit if
overheating occurs.
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