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Modes of Operation
(F1) Units
Note: The F1 units have three main operational
modes:
1. "LEAD/FOLLOW" (As a pair with defrost cycling) For
low temperature operation or otherwise described as
below 32-degree Fahrenheit.
2. "LEAD" Standalone mode with a defrost cycle. For low
temperature operation or otherwise described as
below 32-degree Fahrenheit.
3. "AH" Standalone mode without a defrost cycle.
Typically used for above 32-degree operation.
1. "Lead/Follow" Mode
Notes:
•
In LEAD/FOLLOW mode the unit is designed for low
temperature operation t ypically below 32°
applications.
•
On setup, the first unit should be switch e d to "LEAD"
and the second unit should be set to "FOLLOW".
Another way of thinking about this is as a pair working
together.
•
The fan mode is either VFD or BYPASS (soft start)
depending on the fan selection switch position on the
control cabinet door.
•
Never adjust the defrost cycle timer to longer than that
of the cooling timer value.
Sequence of operation
Each units comes equipped with a filed installable
communication cable. The yellow communication cable
has two five-pin male ends on a 30' yellow cable. The cable
attaches to the female receptacle on the side of the control
panel. The cord is for communications between two
LTAH's for the Lead/Follow operation mode and not used
for standalone operation. Please refer to the image below
for location of communication wire:
At power up if the thermostat is calling for cool the "LEAD"
unit runs in full cooling capacity for 50 minutes (this
12
setting is adjustable from 0.05 seconds to 100 hours but
factory set at 50 minutes) then simultaneously changes to
full defrost capacity for 20 minutes (this setting is
adjustable from 0.05 seconds to 100 hours but factory set
to 20 minutes) and sends a signal through the
communications cable that tells the "FOLLOW" unit to
start its cooling cycle. After the defrost cycle period is over
t he "LEAD" unit sit s idle until the "FOLLOW" unit initiates
its defrost and sends a signal back to the "LEAD" unit that
tells it to start cooling and through the cycle again.
The "FOLLOW" unit sits idle until the "LEAD" unit sends
a 120V signal through the communications cable initiating
a cooling cycle. Then for 50 minutes (adjustable but
factory set at 50) the "FOLLOW" unit runs at full cooling
capacity. After the 50-minute cooling cycle it goes into its
20 minute defrost cycle. At the start of the defrost cycle it
also simultaneously sends a 120V signal through the
communications cable back to the "LEAD" unit and tells it
to start its cooling cycle (all timings are field adjustable).
Then after the "FOLLOW" unit finishes the defrost cycle it
sits idle until told to start again.
When the unit is in the cooling cycle the bypass valve is
energized, allowing the flow of chilled water to pass
through the unit's coil. When the unit is in the defrost cycle
(and while sitting idle) the bypass valve is deenergized
(spring closed) and diverts the flow of chilled water to the
secondary unit via the 3" outlet piping side of the LTAH.
Indefrost cycle the coil and condensate drain pan heating
elements are energized for the prescribed amount of time
(factory set at 20 minutes but field adjustable, see note
below) to thaw the unit. This on-off cycling continues
indefinitely according to the timer settings. The purpose of
cycling from one unit to another in this way is to ensure
that you maintain the necessary cooling capacity to
counter react the heat load in a space. The unit must spend
time in defrost mode to thaw the cooling coil of ice buildup
and keep it from becoming a solid block of ice.
2. "Lead" Mode
Notes:
•
In "Lead" mode the unit is designed to operate
autonomously and is typically for below 32°
applications.
•
The fan mode is either VFD or BYPASS (soft start)
depending on the position of the fan selection switch
located on the control cabinet door.
Sequence of operation
After power up when the thermostat calls for cooling the
bypass valve energizes, allowing the chilled water to flow
through the coil, and the fan comes on. The cooling cycle
will continue until the preset time has expired and the unit
then goes into defrost cycle. When in defrost cycle the fan
shuts off, the bypass valve deenergizes (spring closes) and
the electric defrost heating elements energize. The defrost
cycle is factory set to run for 20 minutes but is field
adjustable. After the d efrost time has expired the LTAH
goes back into the cooling cycle. This cycling from cooling
CHS-SVN011C-EN
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