Unit installation

OMRCPMICRO 31
Pumpdown Control
Pumpdown of each refrigerant circuit will always occur when the circuit is commanded from a "Staging" mode
to an "Off: Ready" mode. The pumpdown sequence closes the solenoid valve and the lead compressor in the
circuit is used to perform the pumpdown. The compressor is fully loaded during pumpdown if unloaders are
present. An alarm condition in the refrigerant circuit will disable the pumpdown sequence.
Pumpdown will occur if the evaporator pressure is above the LPCutIn pressure and stop when the pressure
reaches the LPCutOut pressure. If the evaporator pressure has not dropped to the LPCutOut set point after 180
seconds, the controller will stop all compressors and activate the "Can't Pump Down" alarm output.
Note that pumpdown can be commanded by the operator by moving the circuit switch from "Auto" to
"Pumpdown and Stop". When manual pumpdown is activated, the circuit will pump down once and then shut
off. No additional compressor operation will occur even if the evaporator pressure climbs above the LPCutIn
set point. When the switch is moved to the "Auto" position, the first compressor will start and the unit will
stage up as required if the controller is calling for cooling or heating. If cooling or heating is not requested, the
circuits will pump down and the compressors will stop.
If the chiller is commanded Off by the Time Schedule, Remote Communications or the Remote Stop Switch, the
chiller will pump down and stop when the evaporator pressure falls to the LPCutOut Set Point. In the event
the evaporator pressure rises above the LPCutIn Set Point, the controller will initiate another pumpdown
sequence. After the second pumpdown, the controller will allow only one additional pumpdown to occur
every 120 minutes if required.
"Monitor Only" Sensors and Display Items
The MicroTech controller will shut down the chiller if one of the primary temperature or pressure sensors
should fail. Some secondary "monitor only" sensors provide information to the display but are not critical to
chiller operation. The microprocessor will not activate the external alarm contacts or shut down the unit if one
of the "monitoring only" sensors fails. The display will simply indicate "Short" or "Open" on the
keypad/display for the defective sensor. The "monitoring only" sensors and display items include:
Ø Compressor 1 Suction Temp
Ø Compressor 2 Suction Temp
Ø Evap Water Temp reset signal
Ø Demand Limit signal
Ø Entering Evap Water Temp
Ø Entering Condenser Water Temp (WHR & THR only)
Ø Leaving Condenser Water Temp (WHR only)
Ø Total Unit Amps
Ø Liquid Line Temperature Circuit #1
Ø Liquid Line Temperature Circuit #2
Ø Air Temperature (ALR only)