Unit installation

OMRCPMICRO 37
Normal Sequence of Operation
The following sequence of operation is typical of McQuay models ALR035D through ALR185D and WHR040E
through WHR210E reciprocating water chillers and THR040D through THR170D Templifiers. The sequence
may vary depending on various options which may be installed on the chiller.
Off conditions
With power supplied to the unit, 115 VAC power is applied through the control fuse F1 to the compressor
crankcase heaters (HTR1, HTR2, HTR3 and HTR4), the compressor motor protectors (MP1, MP2, MP3 and
MP4), 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:SystemSw. The controller will then check
the PumpDown Switches. If either switch is in 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:RemoteSw.
The chiller may also be commanded off via the communications network if a separate System Master Panel is
installed. The display will show OFF:RemoteComm 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 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 (ALRs, WHRs, THRs operated in chiller mode)
If none of the above "off" conditions are true, the MicroTech controller will initiate a start sequence. The
chilled water pump output relay 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 "LossofWaterFlow" 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 chilled water temperature and compare it against the
Leaving Chilled Water Set Point, the Control Band and the Load Delay which have been programmed into the
controller's memory. If the leaving chilled water temperature is above the Leaving Chilled Water Set Point plus
1/2 the Control Band plus the adjustable start-up Delta-T setpoint, the controller will select the refrigerant
circuit with the fewest number of starts as the lead circuit and enter the first stage of the Cool Staging mode.
The controller will open the liquid line solenoid valve of the lead refrigerant circuit (SV1 or SV2) allowing
refrigerant to flow through the expansion valve and into the evaporator. When the evaporator refrigerant
pressure rises above the LPCutIn Set Point, the controller will start the first compressor. If additional cooling
capacity is required, the controller will deenergize the unloader. If the load is still not satisfied, the controller
will start the lag refrigerant circuit in the same manner. The compressors and unloaders will automatically be
staged up or down as required to meet the cooling needs of the system. Once the chiller has started, a stage up
in capacity occurs when the leaving chilled water temperature rises above the Leaving Chilled Water Set Point
("Lvg Evap") plus 1/2 the Control Band. The delay between the current cooling stage and the next stage up
request is controlled by the user-adjustable Inter Stage Timer ("InterStg", Menu 16). A stage down occurs
when the water temperature falls below the Leaving Chilled Water Set Point minus 1/2 the Control Band. The
stage down request time delay is a fixed 1/3 ratio of the stage up delay.
If the chiller is operating at minimum capacity (Stage 1) and the chilled water temperature falls below the
Leaving Chilled Water Set Point minus 1/2 the Control Band minus the adjustable shutdown Delta-T setpoint,
the controller will shut off the last operating compressor, enter the Waiting For Load mode, and monitor the
chilled water temperature.