Operator’s Guide
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OM 1263 • MICROTECH UNIT CONTROLLER
Normal Cooling
In the Normal Cooling state the following are accomplished:
• Indoor coil expansion value is modulated to maintain the suction superheat at the suction superheat set point
• Outdoor coil expansion valve is controlled to maintain outdoor coil subcooling at the outdoor coil subcooling set point (heat
pump)
• Outdoor fan(s) are modulated to maintain the discharge saturation temperature at the discharge saturation temperature set
point
When in the Normal Cooling state the action of the cooling control devices is as follows:
Table 38: Normal Cooling State
Device
Action
Compressors
Inverter Compressor Speed Controlled with PI Loop to Maintain DAT Setpoint
Comp 3: Turned On when inverter speed is at Maximum
Comp 3: Turned Off when inverter speed is at Minimum
Outdoor Fan
Outdoor Fan Capacity Controlled With PI Loop to Maintain condensing
temperature setpoint
4 Way Valve
(Heat Pump)
OFF
Outdoor Coil Expansion Valve (EVO) (Heat Pump only)
A
SVR (Heat Pump only)
Closed
SVB
SVB is normally closed during the Normal Cooling state
except in the following cases:
SVB is opened for one second before and after Comp 3 is stopped .
During Low Pressure Unloading Control SVB is opened if PTS< 21 psi .
It is closed again when PTS> 43 psi .
Indoor Coil Expansion Valve (EVI)
EVI Controlled With PI Loop to Maintain Suction Superheat Setpoint
Time Duration
While in Normal Cooling state
A . The outdoor expansion valve position is either driven fully open (100%) or varied based on outdoor coil subcooling as follows:
• When the outdoor expansion valve Method is set to 100%, the outdoor expansion valve is driven to the 100% open
position .
• When the outdoor expansion valve Method is set to subcooling, the outdoor expansion valve is controlled to maintain
the outdoor coil subcooling temperature set point .
Normal Cooling Outdoor Fan (OA Fan PI_Loop)
Control
One or two outdoor fans are controlled via Modbus
connections to the Inverter Compressor Board via the IFB
communication board .
The outdoor fan control PI_Loop is active only during the
Normal Cooling and Cooling Pumpdown operating states and
the loop maintains the discharge saturation temperature at the
set point between a minimum value of 86°F and a maximum
value of 131°F . EER values will be improved by allowing the
lower set points when appropriate .
Normal Heating OA Fan Control
During the Normal Heating state the outdoor fan speed is first
set at the maximum value and is then controlled as follows:
• If discharge pressure is low (below 107 psi) or the INV
Board (fin) Temp is high [above 176°F (172°F for 208/230
volt units) continuously for 15 seconds] the outdoor fan
speed is increased by 2% . No further changes are made
for 15 seconds .
• If discharge pressure is high (above 162 psi) or the INV
Board (fin) Temp is low [below 172°F (169°F for 208/230
volt units) continuously for 15 seconds] the outdoor fan
speed is decreased by 2% . No further changes are made
for 30 seconds .
Outdoor Fan Fault Protection
If a unit is equipped with only one outdoor fan and it is shut off
on one of its internal faults, compressor operation enters the
Standby for Restart state .
If a unit is equipped with two outdoor fans and either outdoor
fan 2 or both outdoor fans shut off on one of their internal
faults, compressor operation enters the Standby for Restart
state . Note: In the case of two fans outdoor fan 2 provides
critical cooling for the inverter compressor/outdoor fan control
boards .
Once compressor operation finishes the Standby for Restart
state and if there is a call for cooling, compressor operation
is allowed to sequence to the Normal operating state in the
normal manner . If this cycle is repeated three times in a thirty
minute period an OA Fan: Problem alarm is generated, locking
out compressor operation, requiring a manual reset.
Summary of Contents for MicroTech III DPS
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