CSZ ZP 16, Installation, Operation & Maintenance Manual, Page: 50 / 88

OPERATION
Page 4-2
PUMPDOWN
Chambers with large horsepower refrigeration systems have an automatic mode of
operation called “pumpdown”. The refrigeration system is in this mode whenever it
is not running to cool or dehumidify the chamber. In pumpdown mode, the system
1 compressor will automatically turn on and off at preset pressures in order to force
refrigerant into the high side of the system. This serves as a means to protect the
compressor on start-up.
If pumpdown was not used, refrigerant could migrate throughout the system and
accumulate, typically in the coldest location like the compressor crankcase. On
start-up, this refrigerant could then enter the compressor as a liquid and cause
permanent damage to the compressor. In addition, a crankcase heater is installed
on the compressor in order to heat the oil in the crankcase of the compressor. This
helps boil out any refrigerant, so that it can be pumped into the high side of the
system.
If the chamber is equipped with the pumpdown mode of operation, the “Pumpdown”
button will be provided on the Alarm Monitor screen. This provides a manual way
to reset pumpdown mode. Pumpdown will be automatically disabled if main power
is off for more than 30 minutes. This is due to the fact that without main power, the
crankcase heater will be off and can not warm the compressor. Depending on the
temperature of the compressor, this could allow refrigerant to accumulate in the
compressor causing a potentially damaging start-up.
The “Pumpdown Disabled” alarm will notify the operator of this condition.
The chamber will not operate when pumpdown is disabled. Pumpdown will
automatically reset after the main power has been on for a period of 4 hours or it
can be reset at any time by pressing the “Pumpdown” button.
If your chamber is equipped with pumpdown, main power should
remain on at all times. If power is removed for extended periods of
non use, DO NOT reset pumpdown after power is applied to the unit.
Only silence the alarm. Allow for the 4 hour warm-up period prior to
use or damage to the compressor may result.
Prior to starting the four
(4) hour pumpdown cycle,
please con
fi rm that the
scroll compressors are
operating in the proper
rotation.
NOTE