AAON RSMV ASM01686, Technical Manual

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13
RSMV Technical Guide
SEQUENCE OF OPERATIONS
Electronic Expansion Valve Operation and Head Pressure Control
Electronic Expansion Valve (EXV)
Operation
If EXV’s are being used, a Coil (Suction Line) Temperature Sensor
will measure the Coil (Suction Line) Temperature after each
Evaporator Coil line for each compressor, and this sensor will be
connected to an RSMV Module. This temperature will be used in
conjunction with the calculated saturated refrigerant temperature
to calculate the Superheat of each evaporator coil. The EXV for
each coil will then be controlled to maintain the Superheat Setpoint.
Head Pressure Control
The RSMV can monitor a Head Pressure Transducer and control a
Condenser Fan to maintain a Head Pressure Setpoint. The RSMV
must be configured for an Air Cooled Condenser.
A Condenser Relay is commanded on when the first compressor is
enabled (except if the unit is in Heat Pump Defrost Mode). On an
Air Cooled Unit, the Condenser Fan will be controlled with 0-10
VDC output signal.
When the Condenser Signal first activates, it maintains at 100%
for 10 seconds.
In the Cooling Mode, the Condenser Signal will modulate to maintain
the Cooling Head Pressure Setpoint. The signal can modulate
between 15% and 100%. If the Head Pressure exceeds 550 psig,
the condenser control signal will immediately go to 100% and a
High Head Pressure Alarm will be generated. The alarm will be
deactivated when the Head Pressure drops below 540 psig.
In the Dehumidification Mode, the Condenser Output Signal controls
to the Reheat Head Pressure Setpoint. High Head Pressure conditions
produce the same effects as in the Cooling Mode.
If no Head Pressure Sensor is detected, the Condenser Output Signal
will be maintained at 100%.