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Scholar V VAIVA Maintenance & Service Manual 10/2017 Rev.2
11. SCREEN 11: Head Pressure Control
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Condenser blower cycling is used to control head pressure (condenser temperature).
Proper operation in cooling requires that the condenser temperature (pressure) be maintained
above a certain minimum value. This can become a problem in cooler weather as the cool
ambient temperatures tend to drive the condenser temperature below an acceptable minimum
value. Head pressure control (control of condenser pressure and saturated temperature) is
used to keep the values at or above an acceptable minimum value.
The purpose of the condenser coils is to transfer rejected heat to the outside ambient air.
Two condenser blowers are used to move outside air over the outdoor heat exchanger coils.
The condenser pressure drops as airflow increases and increases as airflow is reduced. Two
thermocouples are embedded in the condenser distributor tube bundles, one for each of the
two condensers. The temperature measured by these thermocouples closely approximates
the condenser temperature (which is in correspondence with condenser pressure). As the
temperature falls to a predetermined level (OFF point), the PLC cycles off one or both blowers.
When a blower cycles off, the condenser temperature (head pressure) begins to rise. When
the temperature rises to the ON point, the blowers operate again.
Settings example:
