McQuay AGS 206A, Operation Manual

Page: 34 / 66

34 OM AGSB-5
Table 23, Circuit Stop Alarms
Description Occurs When: Action Taken
No Pressure at Start
Evap or Cond pressure< 7 psi when Compressor Start
Requested
Start Aborted,
Circuit Locked Out
on Manual Reset
Low Evaporator Pressure
[Freezestat trip OR Evaporator Press < 0 psi OR Low
Pressure Sw Open] AND Compressor State = Run
Rapid Stop
High Lift Pressure
Cond Sat Temp > Max Sat Cond Value for a period
exceeding the setting of the High lift Delay timer
Rapid Stop
Mechanical High Pressure Digital Input 6 = Open Rapid Stop
Below Minimum Lift Pressure
Cond Press < Min Sat Cond Value for time > Min Lift
Delay SP
Pumpdown
High Discharge Temperature Temp > High Discharge Temperature SP Rapid Stop
Low Oil Level
DI9 = Open for Time greater than Low Oil Level Delay
+ the Low Oil Level Event has occurred in the past
hour
Rapid Stop
High Oil Pressure Difference
Digital Input 5 = Open for time greater than High
Press Diff Delay SP
Rapid Stop
Starter Fault (Note) Digital Input 3 = Open Rapid Stop
Evaporator Press. Sensor Fault Sensor shorted or open Rapid Stop
Condenser Press. Sensor Fault Sensor shorted or open Rapid Stop
Liquid Line Pressure Sensor Fault Sensor shorted or open Pumpdown
Discharge Temp. Sensor Fault Sensor shorted or open Pumpdown
Liquid Line Temp. Sensor Fault Sensor shorted or open Pumpdown
Slide Position Sensor Fault Sensor shorted or open Pumpdown
NOTE: As long as starter communication is functioning, power data will be displayed and starter
faults will be indicated. Some starter faults are self-clearing in the starter itself. Alarms triggered by
these faults will be allowed to self-clear twice per day. The third will trigger a manual reset in the
controller requiring it to be cleared via the active alarm screens on the unit controller. Alarms using
this logic are:
Current Imbalance Current low Phase Loss Phase Reversal
Voltage High Voltage Low No Starter Transition Other Starter Faults
Some starter faults never auto-clear in the starter. They can be clearedvia the Active Alarm screens
on the unit controller or on the starter itself. Alarms using this logic are:
High Current Trip Ground Fault High Motor Temperature
Evaporator Freezestat
Freezestat logic allows the circuit to run for varying times at low pressures. The lower the
pressure, the shorter the time the compressor can run. This time is calculated as follows:
Freeze error = Low Evaporator Pressure Unload – Evaporator Pressure
Freeze time = 60 – 6.25 x ( Freeze error ), limited to a range of 10-60 seconds
When the evaporator pressure goes below the Low Evaporator Pressure Unload setpoint, a
timer starts. If this timer exceeds the freeze time, then a freezestat trip occurs. If the
evaporator pressure rises to the unload setpoint or higher, and the freeze time has not been
exceeded, the timer will reset.
The following two values are designed to keep the compessor in its design operating
envelope.
Maximum Saturated Condenser Value
If Sat Evap Temp < 32 then
Max sat cond value = 155 + 1.588(Sat Evap Temp – 32)
If [Sat Evap Temp >= 32 AND Sat Evap Temp < 40] OR Circuit State = Pumpdown then
Max sat cond value = 155
If Sat Evap Temp >= 40 AND Sat Evap Temp < 55 then
Max sat cond value = 155 – 0.667(Sat Evap Temp – 40)
If Sat Evap Temp >=55 then
Max sat cond value = 145