McQuay AGS 206A, Operation Manual

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OM AGSB-5 7
EvapRecTimer
The evaporator recirculation timer establishes the length of time the chilled water pump will
run after the controller receives an enable signal and the Wait for Flow timer time out. This
period allows time for the chilled water to circulate sufficiently to determine if there is a
need for cooling.
EXV
Electronic expansion valve, used to control the flow of refrigerant to the evaporator,
controlled by the circuit microprocessor.
High Saturated Condenser – Hold Value
High Cond Hold Value = Max Saturated Condenser Value – 5
°
F
This function prevents the compressor from loading whenever the pressures approach
within 5 degrees of the maximum discharge pressure. The purpose is to keep the
compressor online during periods of possibly temporary elevated pressures.
Low OAT Start
Allows start attempts at low ambient temperatures.
High Saturated Condenser – Unload Value
High Cond Unload Value = Max Saturated Condenser Value – 3
°
F.
This function unloads the compressor whenever the pressures approach within 3 degrees of
the maximum discharge pressure. The purpose is to keep the compressor online during
periods of possibly temporary elevated pressures.
Low Pressure Hold Setpoint
The psi evaporator pressure setting at which the controller will not allow further compressor
loading.
Low/High Superheat Error
The difference between actual evaporator superheat and the superheat target.
LWT
Leaving water temperature. The “water” is any fluid used in the chiller circuit.
LWT Error
Error in the controller context is the difference between the value of a variable and the
setpoint. For example, if the LWT setpoint is 44
°
F and the actual temperature of the water
at a given moment is 46
°
F, the LWT error is +2 degrees.
LWT Slope
The LWT slope is an indication of the trend of the water temperature. It is calculated by
taking readings of the temperature every few seconds and subtracting them from the
previous value, over a rolling one minute interval.
Maximum Saturated Condenser Temperature
The maximum saturated condenser temperature allowed is calculated based on the
compressor operational envelope.
Mode
There are three possible operating modes for the unit: Some can be combined and then
selected by an external signal or from the keypad.
1. Cool, the compressors are under normal unloading and staging control and the
minimum LWT setpoint is 40
°
F. Cool with Glycol merely reduces the minimum LWT
to 30
°
F.
2. ICE, primarily controls the compressor at full load until the LWT setpoint is reached,
then shuts unit off.
3. Test, allows outputs to be actuated manually.