MP-3000 Controller
64
• Evaporator fans operate on high speed at
setpoints of -9.9 C (14.1 F) and above.
• Evaporator fans operate on low speed at
setpoint temperatures of -10 C (14 F) and
below.
• About 10 seconds later, the compressor starts
and the liquid line solenoid energizes (opens)
if the controller calls for cooling.
• The condenser fan then starts if the condenser
temperature requires condenser fan operation.
• If the controller calls for heating, the electric
heaters are pulsed on and off to provide heat.
• The controller turns on the In-range LED
when the controlling sensor temperature is
within 1.5 C (2.7 F) of the setpoint.
NOTE: Random time delays during the
initial unit start-up minimize peak current
draw.
Continuous Temperature Control
Operation
Chill Loads (Controller Setpoint at -9.9 C
[14.1 F] and Above):
The controller regulates the compressor, stepper
motor valve and electric heaters based on a
Control Temperature Differential (see “General
Theory of Operation” in this chapter for more
detail). This means the unit operating mode can
not be predicted based only on the setpoint and
supply air temperature.
At setpoints of -9.9 C (14.1 F) and above, the
controller operates the unit on:
• Cool mode with Modulation
• Controller energizes the liquid injection valve
continuously when the modulation capacity is
91% or less.
• Controller energizes the warm gas bypass
valve when the modulation capacity is
approximately 50% or less.
• Controller energizes (closes) the
coil/dehumidify valve when the modulation
capacity decreases to 20%. The valve remains
closed until the modulation capacity increases
to 25%.
• Heat mode (electric heaters pulse on and off
on a 60 second duty cycle).
• Defrost mode (electric heaters on, evaporator
fans off).
A.
Cool with Modulation* (control temperature
differential is above setpoint)
B.
Heat (electric heaters pulse on and off on a 60
second duty cycle if the return air temperature
decreases to 0.3 C [0.5 F] above setpoint; or
the supply air temperature is too low)
C. In-range (based on supply air temperature)
1. Decreasing Temperature
2. Setpoint
3. Increasing Temperature
*Controller also energizes liquid injection valve and
warm gas bypass valve as modulation capacity
decreases.
Figure 22: Chill Load Control Sequence
(Setpoints at -9.9 C [14.1 F] and Above)
AXA0156
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