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PSIO Software Version 09 and Higher
The oil heater relay is energized whenever the chiller compressor is off and the oil sump
temperature is less than 150 F (65.6 C) or the oil sump temperature is less than the cooler
refrigerant temperature plus 70° F (39° C). The oil heater is turned off when the oil sump
temperature is either 1) more than 160 F (71.1 C); or 2) the oil sump temperature is more than
155 F (68.3 C) and more than the cooler refrigerant temperature plus 75° F (41.6° C). The oil
heater is always off during start-up or when the compressor is running.
When a power failure to the PSIO module has occurred for more than 3 hours (i.e., initial
start-up), the oil sump is heated to 100° F (56° C) above the evaporator refrigerant temperature
or 190 F (88 C), whichever is lower. Once this temperature is reached, the oil pump will be
energized for 1 to 2 minutes or until the oil sump temperature cools to below 145 F (63 C). The
normal heating algorithm is now followed once ramp loading has been completed.
After a 3-hour power failure, the oil temperature must rise to the higher oil temperature. The
controls will delay the start of the compressor until this temperature is met.
Oil Cooler
The oil must be cooled when the compressor is running. This is accomplished through a
small, plate-type heat exchanger located behind the oil pump. The heat exchanger uses liquid
condenser refrigerant as the cooling liquid. A refrigerant thermal expansion valve (TXV)
regulates refrigerant flow to control oil temperature entering the bearings. There is always a flow