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RSM-DEV1 Technical Guide
SEQUENCE OF OPERATIONS
Component Operation
Electronic Expansion Valve Operation
EXV operation is fully integrated into the superheat controller. The
superheat controller measures suction pressure and temperature
to determine superheat and automatically modulates the EXV to
maintain the configured superheat. The RSM-DEV1 communicates
with the superheat controller to set the desired Superheat Setpoint
and to retrieve operational data for display and trending purposes.
Head Pressure Control
The RSM-DEV1 can monitor a head pressure transducer and control
a condenser fan to maintain a Head Pressure Setpoint.
The condenser fan starting speed varies based on outside air
temperatures. At 40°F or colder the fan starts at 10%; at 70°F
or warmer the fan starts at 100%. Starting speed adjusts linearly
between 40 and 70 degrees.
In Cooling Mode, the condenser fan modulates speeds to target the
discharge pressure setpoint based on the highest running circuit it
is controlling. This is also true for Dehumidification Mode and has
a separate discharge pressure setpoint adjustable in Prism 2.
In Heat Pump Heating, the outside fan modulates speeds to target the
outside approach temperature setpoint which is outside temperature
minus the lowest saturation temperature of the running circuit it is
controlling.
If the pressure exceeds 575 psig, the circuit shuts down in an attempt
to fail before the mechanical high pressure switch opens. The circuit
is allowed to restart after five minutes.
If no head pressure is detected on a circuit, the compressor is
disabled and not allowed to run. If the head pressure reading is
lost while circuit is on, the condenser signal goes to 100% until the
compressor shuts down.
