Schreiber Chillers 1055 New - Manual (Page 29)

Compressor
The compressor is a high efficiency compliant scroll compressor. It is hooked to the refrigeration
system with rotor lock valves. The rotor lock valves contain a double seating shut off valve and an
access port. The valve is shipped from the factory in the fully open (back seated) position and should
remain in this position during normal operation. Crankcase heaters are installed on the compressors
and are always energized.
The compressor has a minimum run time, and a minimum off time parameter set in the controller to
prevent short cycling.
Condenser System
The condensing unit contains a dual circuited aluminum fin condenser, two condenser fans, and a
variable speed drive.
Head Pressure Control
Constant head pressure is maintained by adjusting the speed of the condenser fans to match the
chiller load and the entering air temperature. The controller reads the head pressure of both systems
simultaneously, and determines the fan speed based on the highest of the two pressures. In the event
of a failure of a pressure sensor, the controller will ignore the pressures and disable the variable
speed feature. This will force the fan to run full speed at all times.
If the speed calculated by the controller is lower than the minimum frequency allowed, the fans will
completely turn off.
The parameters in the variable speed drive itself are factory set and should not have to be changed
for any reason.