Is the liquid injection solenoid (8sol) opening and is the oil TXV feeding? And if so, is there a solid liquid head to the TXV?
I have an old catalog showing the low discharge temp switch
(8tas) has to be made for the solenoid to energize. Is the oil heating up under low loads with the slide valve backed off?
I am ex Dunham-Bush service rep and Icemiester is right!!! All screw chillers are very critical to discharge superheat and your problem is high oil temp - check that expansion valve to the oil and your oil cooler!!!!!
I gave the customer a quote on changing the fan staging.
The building has 3chillers ,1apcx (air cooled)2 pcx chillers (water condersors) that heat and cool the building the third the one the apcx the one with problems is used during the summer months to reduce run time on the other two chillers.During the day the load requires two chiller to be on line but at night the load drops to the point were each chiller is at 10%.