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Controls Training and Service Manual
Fan Alarm / Fan settings
The fan operation is controlled by two (2) digital devices: the Loss of Airflow
differential pressure switch and the Main fan Overload motor protection. The
time delay at the unit start is always 5 seconds shorter than the control delay.
High Pressure Cutout
The control uses high head lockout functionality. If one compressor trips or is
locked out on high head, the other compressor turns on when the space
temperature increases 1°F. Pressing the alarm button on the display twice can
reset high head Alarm. A lockout condition occurs on the third trip and must be
reset by turning the main power switch to off then back on
.
Suction Pressure Transducer
The suction pressure transducer operation is only on air conditioning products (not
chiller applications). Transducer measurements are made at least once every 1
second. With all other operating times for all compressors, additional
measurements, shall be taken based on operation “at limit conditions” for 5
seconds and shall not include readings taken during Pumpdown or Winter Start
Kit (WSK) timeout
.
Call for Cooling
The following applies for both R22 and R407C systems and applies to all
compressor types. The call for cooling opens the Liquid Line Solenoid Valve
(LLSV). Note: on units with Digital Scroll Compressors the unloader is energized
0.1 second before the compressor contactor is energized. On air-cooled units with
fan speed type condenser (FSC) the low pressure start threshold is 35psiG
(50psiA). On air-cooled units with lee-temp control (LT) and all fluid cooled
units the low-pressure start threshold is 60psiG (75psiA).
All compressorized units use the following start
sequence:
Open LLSV, if WSK is set to 0, wait for suction pressure to reach setting, then start
compressor and freeze protection timer.
If WSK is set greater than 0, operate the compressor for the WSK override time
and monitor suction transducer value.
If pressure is achieved the compressor is allowed to operate, and the freeze
protection timer is started.
If pressure is not achieved, turn compressor off and leave LLSV open.
If pressure is achieved within next 30 seconds the compressor is allowed to
operate, and the freeze protection timer is started.
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