MP-3000 Controller
66
7
Dehumidification Option: When the Dehumidify
mode is set to On, the supply air temperature must
be In-range to close (energize) the
coil/dehumidify valve:
• When the humidity is 2% or more above
humidity setpoint, the controller closes
(energizes) the coil/dehumidify valve.
• When the humidity is more than 5% above
humidity setpoint, the controller also pulses
the electric heaters on and off.
8
Controller energizes electric heaters for frost
protection, heat, defrost and dehumidification
7
:
• Frost Protection (cooling): If return air
temperature is within 0.3 C (0.5 F) of setpoint,
heaters pulse on and off on a 60 second duty
cycle.
• Heat mode (compressor off): If supply air
temperature is too low, heaters pulse on and
off on a 60 second duty cycle.
• Defrost mode: Heaters are on until evaporator
coil temperature increases to terminate
defrost.
Cool with Modulation
• Controller calls for the Cool mode whenever
the Control Temperature Differential (based
on supply air temperature) is above setpoint.
• Controller turns on the Compressor LED
when the compressor is operating.
• Controller opens and closes stepper motor
valve to regulate the flow of refrigerant to the
compressor. The position of the stepper motor
valve balances the unit cooling capacity
against the actual load requirements.
• Controller turns on the In-range LED when
the supply air sensor temperature is within
1.5 C (2.7 F) of setpoint.
• Supply air sensor control algorithm increases
temperature control accuracy and protection
against frost damage (see “Chill Loads” under
“General Theory of Operation” in this
chapter).
• Controller pulses electric heaters on and off
for additional frost protection if the return air
temperature decreases to within 0.3 C (0.5 F)
of setpoint (see “Chill Loads” under “General
Theory of Operation” in this chapter).
• Controller turns on the Heat LED whenever
the heaters are pulsed on and off.
Heat
• If the supply air temperature is too low and the
Control Temperature Differential is above the
setpoint, the controller stops the compressor
and pulses the electric heaters on and off on a
60 second duty cycle to provide heat. The
controller pulses the electric heaters on and off
until the supply air temperature increases to
setpoint.
Frozen Loads (Controller Setpoint
at -10 C [14 F] and Below):
At setpoints of -10 C (14 F) and below, the
controller locks out the Modulation and Heat
modes. The controller regulates compressor
operation based the return air sensor and setpoint
temperatures.
At setpoints of -10 C (14 F) and below, the
controller operates the unit on:
• Cool mode
• Null mode
• Defrost mode (electric heaters on, evaporator
fans off)
• Evaporator fans operate on low speed and
continuously circulate air inside the container
(except during Defrost; or when Economy
mode is on and the unit is in Null mode). See
“evaporator Fan Control” on page 63, or
“CSR Operating Mode Function.
• Controller LED display shows the return air
sensor temperature.
• Controller LCD display shows the setpoint
temperature.
• Controller cycles a single-speed condenser fan
on for 2 to 30 seconds every 30 seconds when
the unit is on air-cooled condenser operation.
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