Particular notes on safe compressor and system operation

Analysis show that compressor failures are most often due to an unsafe operation mode. This applies especially to damage resulting from lack of lubrication:

• Function of the expansion valve – observe the manufacturer's notes!
• Position the temperature sensor correctly at the suction gas line and fix it.
• When using an internal heat exchanger, position the evaporator's expansion valve sensor prior the internal heat exchanger.
• If possible, insulate the sensor to ensure it measures the suction gas line temperature and not the ambient temperature.
• Provide sufficient suction gas superheat according to the Bitzer Software and its application remarks.
• A high suction gas superheat setting of the expansion valve may result in high discharge gas temperatures, reduced refrigerating capacity and poor oil return.
• A low suction gas superheat may cause liquid slugging and compressor bearing washout.
• When using electronic expansion devices, enabling the MOP (maximum operating pressure) feature is strongly recommended to avoid overloading the compressor. Set the MOP value to the maximum allowable evaporating pressure according to the saturated temperatures of the compressor application limits. Some thermostatic expansion valves also offer a MOP function.
• Ensure a stable operation mode under all operating and load conditions (also part load, summer/winter operation, minimum speed during operation with frequency inverter).
• Bubble-free liquid at the expansion valve inlet. Bubbles can destroy the nozzle of the expansion valve due to cavitation forces and reduce the refrigerating capacity.

• Avoid refrigerant migration (from the high pressure side to the low pressure side or into the compressor) during long shut-off periods!
• Install a solenoid valve in the liquid line.
• An automatic pump down system (Pump down system) is recommended before any off cycle (especially if the evaporator may get warmer than the suction gas line or the compressor), as long as the pressures are within the application limits.
• Install a sufficiently sized suction accumulator to prevent liquid slugging caused by liquid floodback during compressor start.
• Observe the low pressure limit.
• Automatic sequence change for systems with several refrigerating circuits.
• An oil heater is generally recommended and should be turned on during standstill and at least 12 h prior to the first compressor start. For further details: Pipe layout and further components.

• For reverse cycling:
• First switch off the compressor.
• Reverse the system by switching the required system components.
• Wait for 30 s.
• Then start the compressor.