Product manual

70 IOMM ACR/AGR-1
Sequence of Operation
Off Conditions
With power supplied to the unit, 115Vac power is applied through the control fuse F1 to the
compressor crankcase heaters (HTR1-4), the compressors motor protectors (MP1-4), the evaporator
heater and the primary of the 24V control circuit transformer. The 24V transformer provides power to
the MicroTech controller and related components. With 24V power applied, the controller will check
the position of the front panel System Switch. If the switch is in the “stop” position the chiller will
remain off and the display will indicate the operating mode to be OFF:System Sw. The controller will
then check the PumpDown Switches. If either switch is n the “stop” position, that circuit’s operating
mode will be displayed as OFF:PumpDownSw. If the remote Start/Stop Switch is open, the chiller will
be OFF:Remote Sw. The chiller may also be commanded off via the communications network if a
separate System Master Panel is installed. The display will show OFF:Remote Comm if this operating
mode is in effect.
If an alarm condition exists which prevents normal operation of both refrigerant circuits, the chiller will
be disabled and the display will indicate OFF:Alarm.
Assuming none of the above “OFF” conditions are true, the controller will examine the internal time
clock schedule to determine if the chiller should start. The operating mode will be OFF:TimeClock if
the time schedule indicates an “OFF” time period.
Start - Up
If none of the “OFF” conditions are true, the controller will initiate a start sequence. The chilled water
pump relay output is energized any time the chiller is enabled and the chiller will remain in the
“Waiting For Flow” mode until the field installed flow switch indicates the presence of chilled water
flow. If flow is not proven within 30 seconds, the alarm “Loss of Water Flow” will be activated and the
chiller will continue to wait for proof of chilled water flow. Once flow is established, the alarm will
automatically be cleared and the unit will go into the “Wait For Load” mode.
Once flow is established, the controller will sample the leaving water temperature and compare it
against the leaving water temperature set point, the control band, the start up delta T and the start
timers. If all values indicate a start (stage 1 cooling), the controller will start the lead compressor by
energizing that circuit's liquid line solenoid valve (SV). When the circuit pressure exceeds the LPCutIn
pressure, the compressor on that circuit will be started. If additional cooling is required (stage 2
cooling), the controller will energize the lag circuit liquid line solenoid valve (SV). When that circuit’s
pressure exceeds the LPCutIn pressure, the compressor will be started. If additional cooling is
required (stage 3 through 6 cooling), compressor unloaders will be energized or deengized.
When the evaporator water temperature is satisfied, the reverse will occur with the compressor with
the most run hours being stopped in each stage down. If the chiller is operating at minimum capacity
(stage 1) and the chilled water temperature falls below the Leaving Evap Water Set Point, control band
and shut down delta T, the controller will stop the last operating compressor. The controller enters the
“Waiting For Load” mode and monitor the leaving water temperature.