Unit installation

34 OMRCPMICRO
Low evaporator pressure
If during a non-low ambient start, the evaporator pressure fails to rise above the Low Pressure Cut In Alarm
Set Point (LP CutIn) within 80 seconds of the liquid line solenoid valve opening or, if during the cooling mode
the evaporator pressure falls below the Low Pressure Cut Out Alarm Set Point (LP CutOut), a "Lo Evap
Pressure" alarm will be generated. This alarm will also occur if the evaporator pressure drops to 2 psi for more
than 20 seconds during low ambient start.
Oil differential/power
Comp#1 LowOil/Pwr
Comp#2LowOil/Pwr
Comp#3LowOil/Pwr
Comp#4LowOil/Pwr
Each compressor is equipped with an oil differential pressure switch which closes when the net oil pressure
reaches 14 psig. The controller will initiate a shutdown of all compressors in a circuit should one of the
compressors in that circuit lose adequate oil pressure. Loss of oil pressure is detected when the oil pressure
differential switch opens at 9 psig and this condition remains true for more than 30 consecutive seconds. If the
switch re-closes before 30 seconds has elapsed, the timer is reset.
In addition, if a compressor never starts due to a tripped line voltage circuit breaker, the controller will think the
compressor is running when it actually is not. After 30 seconds, the above alarm will catch this condition, thus
the term "LowOil/Pwr".
Refrigerant freeze protection
If the saturated evaporator refrigerant pressure falls below the operator adjustable refrigerant freeze set point
(Frz Stat) for a time period equal to the freezetimer set point (FreezeTim), the alarm will be "Freeze Stat Prot".
This is true if the Freeze Timer is set at 30 seconds. If it is set higher (the default is 80 seconds), the controller
will initiate a pre-alarm condition of "FreezeProtStgDwn" after the first 30 seconds and force the unit to stage
down in capacity every 10 seconds until the pressure rises above the Frz Stat set point or until stage 1 cooling
is reached. The unit will stay at stage 1 cooling until the saturated evaporator pressure rises above Frz Stat set
point or until the Freeze Timer times out at which point the unit will go into the "Freeze Stat Prot" alarm.
Incomplete pumpdown
If the controller remains in a pumpdown operation for more than 180 seconds, the pumpdown operation is
aborted and the circuit is shut down. The alarm "Can't Pump Down" is registered. This alarm can occur when
a solenoid valve sticks open or some other refrigerant circuit problem exists. The pressure to which the
compressor pumps down to is regulated by the Low Pressure Cut Out alarm set point (LP CutOut).
Bad pressure sensor
If the Evaporator Pressure Transducer or the Condenser Pressure Transducer signal is shorted to ground or
open, the alarm "Bad Evap PresSen" or "Bad Cond PresSen" is logged on the MicroTech display, whichever is
appropriate. The circuit is locked out until the alarm is manually reset.