Carrier 19XL - Manual (Page 84)

High Discharge Temperature Control
If the discharge temperature increases above 160 F (71.1 C) (PSIO Software Version 09 and
higher) or 180 F (82 C) (PSIO Software Version 08 or lower), the guide vanes are proportionally
opened to increase gas flow through the compressor. If the leaving chilled water temperature is
then brought 5° F (2.8° C) below the control set point temperature, the controls will bring the
machine into the recycle mode.
Oil Sump Temperature Control
The oil sump temperature control is regulated by the PIC which uses the oil heater relay
when the machine is shut down.
As part of the pre-start checks executed by the controls, oil sump temperature is compared
against evaporator refrigerant temperature. If the difference between these 2 temperatures is
50 F (27.8 C) or less, the start-up will be delayed until the oil temperature is 50 F (27.8 C) or
more. Once this temperature is confirmed, the start-up continues.
PSIO Software Version 08 and Lower
The oil heater relay is energized whenever the chiller compressor is off, and the oil sump
temperature is less than 140 F (60 C) or sump temperature is less than the cooler refrigerant
temperature plus 60° F (33.3° C). The heater is then turned off when the oil sump temperature
is: 1) more than 160 F (71.1 C); or 2) the sump temperature is more than 145 F (62.8 C) and
more than the cooler refrigerant temperature plus 65° F (36.1° C). The heater is always off
during start-up or when the compressor is running.