1-15
DataCORDER Key
Display (Optional)
Hours Since Last
Hours since last trip start.
Trip Start
Trip Start
Initiates
Trip
Start
(when
pressed simultaneously with
hours since last trip start).
1.13.3 Microprocessor Temperature Control
There are two control ranges Frozen and Perishable.
The Frozen range is active with set points at or
below
---10
_
C (+14
_
F) and the Perishable range is active at set
points
above ---10
_
C (+14
_
F). See Figure 1-9 and
Figure 1-10.
a. Perishable range above ---10
_
C (+14
_
F).
For set points above ---10
_
C (+14
_
F), the controller
will maintain supply air at the set temperature by the
following modes of operation:
1. Conventional, Dehumidification Control (Code
32 OFF) --- cooling by refrigeration with suction
modulation and the compressor cycling at light loads.
Electric resistance heating.
2. Conventional plus Dehumidification, Humidity
Control (Code 32 ON) --- cooling by refrigeration with
suction modulation and compressor cycling at low
humidities, suction modulation and simultaneous
electric resistance heating at high humidities.
1. Operation in the Conventional Mode
(Code 32 OFF)
The supply probe is used for control and is so
indicated by the LED on the display board. The
Perishable temperature range demands high accuracy.
The system is capable of maintaining supply air
temperature to 0.25
_
C (+0.5
_
F) of the set point
temperature setting. The compressor is energized
continuously to ensure a steady and stable supply air
temperature to the container. In Perishable range
above
---10
_
C (+14
_
F)
control is maintained by controlling the
positions of the solenoid modulation valve (SMV) and
suction solenoid valve (SSV, on 69NT40 only).
When pulling down to set point, both valves will be
open to reduce the pulldown time unless suction solenoid
override is activated. See section 1.11 for explanation of
suction solenoid override. The current limit function will
override if the current is above the selected value, and
restrict the valves. When the temperature reaches set
point, the suction solenoid valve will close.
As the temperature enters the in-range temperature
tolerance, the in-range light will energize.
The controller logic is designed so the solenoid
modulating valve will begin to close as set point is
reached. The modulation valve will close to restrict
refrigerant flow until the capacity of the unit and the load
are balanced.
If the temperature drops below set point, the
compressor will remain running for a few minutes. This is
to accommodate any initial overshoot which might occur.
After this time and at 0.2
_
C (0.4
_
F) or greater below set
point, the compressor will be turned OFF.
The heaters will be energized if the temperature
drops to 0.5
_
C (0.9
_
F) below set point. The heaters will
de-energize when the temperature rise to 0.2
_
C (0.4
_
F)
below set point. The compressor will not restart until the
temperature rise to 0.2
_
C (0.4
_
F) above set point, and
the 6 minute time delay has been satisfied.
2. Operation in the Dehumidification Mode
(Code 32 ON) --- Optional
The dehumidification mode is activated by selecting
Code 32 and pressing the
Enter
key to display “ON.” The
control probe LED (supply 1) will flash ON and OFF
every second to indicate the dehumidification mode is
active. Once the Mode is active and the following
conditions are satisfied, the controller will activate the
heat relay to begin dehumidification.
1. The humidistat is calling for dehumidification.
(ie., HCS is closed and 24 vac is at plug Pd23.)
2. The pulldown mode is NOT active. (ie., The
bypass valve is closed.)
3. The control probe (ie., Supply 1) temperature is
less than or equal to se.25
_
C.
4. The system is in the control mode and the
compressor is running.
This applies power to the defrost and drain pan
heaters. This added heat load causes the controller to
open the modulating valve to match the new total heat
load while still holding the supply air temperature very
close to set point.
Opening the modulating valve reduces the
temperature of the evaporator coil surface which
increases the rate water is condensed from the air passing
through the coil. Removing water from the air reduces
the relative humidity until the HC setting is reached and
controller de-energizes the heat relay.
Humidity controller HC will continue to cycle
heating to maintain relative humidity below HC setting.
Two timers are provided in the Dehumidification
mode to prevent rapid mode switching and consequent
contactor wear. They are:
1. Heater debounce timer (3 minutes).
2. Out-of-range timer (5 minutes).
The heater debounce timer is activated whenever the
contactor status is changed. The contactor remains
energized (or de-energized) for at least 3 minutes even if
the humidistat switch (HCS) opens (or closes). This is to
prevent rapid cycling of the heat contactor when the
humidistat approaches setpoint.
If the mode is
terminated by a condition other than the humidistat
switch (HCS). For example, an out-of-range condition or
compressor shutdown, the heat relay is de-energized
immediately.
The out-of-range timer is provided to allow the
heaters to remain energized during a temporary
out-of-range condition. If the control probe remains
out-of-range for more than 5 minutes, the heaters will be
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