1.Inspection items for cold storage screw compressors
（1）Check whether there are abnormal wear marks on the inner surface of the body and the surface of the slide valve, and measure the size and roundness of the inner surface with an inner diameter dial gauge.
（2）Check whether there are wear marks on the end faces of the main and driven rotors and the suction and exhaust end seats.
（3） Check the wear of the outer diameter and tooth surface of the main and driven rotors, and measure the outer diameter of the rotor with an outer diameter dial gauge.
（4） Measure the diameter of the main shaft of the rotor and the inner diameter of the main bearing hole, and check the wear of the main bearing.
（5） Check the wear of the shaft seal.
（6）Check all “o” rings and springs for deformation and damage.
（7）Check the condition of all internal oil circuits of the compressor.
（8） Check whether the energy indicator is damaged or blocked.
（9） Check the oil piston and balance piston for abnormal wear.
（10）Check whether the transmission core or diaphragm of the coupling is damaged.
2.Maintenance and failure of screw refrigerator
A. Low cold water flow alarm
The cold water target flow switch is not closed, check and adjust the flow switch.
The cold water pump is not turned on.
The shut-off valve of the cold water pipeline is not open.
B. Oil pressure alarm
Running out of oil and even oil level switch alarm, oil pressure alarm, oil pressure difference alarm.
For long-term operation under low load conditions, the best way is to keep the unit running at full load.
The cooling water temperature is low (less than 20 degrees), making it difficult to maintain oil supply by pressure difference.
C. Low suction pressure alarm
The low pressure sensor fails or has poor contact, check or replace it.
Insufficient refrigerant charge or unit leakage, check and charge.
Clogged filter drier, disassemble and clean.
When the opening of the expansion valve is very small, the stepping motor is damaged or has poor contact, check, repair or replace it.
D. High exhaust pressure alarm
If the cooling water is not turned on or the flow is insufficient, the flow can be increased;
The cooling water inlet temperature is high, check the cooling tower effect;
The copper pipes in the condenser are seriously fouled, and the copper pipes should be cleaned;
There is non-condensable gas in the unit, discharge or vacuumize the unit;
Excessive refrigerant can be recovered to the required amount of refrigerant;
The partition plate in the condenser water chamber is half-through, repair or replace the water chamber gasket;
The high pressure sensor fails. Replace the sensor.
E. Oil pressure difference fault
The economizer or oil pressure sensor fails, check it and replace it.
The internal and external filters are clogged, replace the filter.
Oil supply solenoid valve failure. Check coil, solenoid valve, repair or replace.
The oil pump or one-way valve of the oil pump group is faulty, check and replace.
F. Judging that the refrigerant charge is insufficient
requires attention! The sight glass on the liquid pipe shows that the bubbles are not enough to judge the lack of refrigerant; the temperature of the saturated steam is not enough to judge the lack of refrigerant; it can be judged by the following methods:
Confirm that the unit is running under 100% load conditions;
Confirm that the temperature of the cold water outlet of the evaporator is between 4.5 and 7.5 degrees;
Confirm that the temperature difference between the cold water inlet and outlet of the evaporator is between 5 and 6 degrees;
Confirm that the heat transfer temperature difference in the evaporator is between 0.5 and 2 degrees;
If the above conditions are not met, and the opening of the electronic expansion valve is greater than 60%, and the sight glass shows bubbles, this article comes from Refrigeration Encyclopedia, based on which it can be judged that the unit lacks refrigerant. Do not overcharge with refrigerant, as this will result in high discharge pressure, more cooling water consumption, and possibly damage to the compressor.
G. Add refrigerant
In order to confirm that enough refrigerant is added, it is necessary to make the unit run continuously under 100% load conditions, so that the temperature of the cold water outlet of the evaporator is 5~8 degrees, and the temperature difference between the inlet and outlet water is between 5~6 degrees. The judgment method can refer to the following:
The expansion valve opening is between 40% and 60%;
The heat transfer temperature difference of the evaporator is between 0.5 and 2 degrees;
Confirm that the unit is operating under 100% load conditions; .
Add liquid with the liquid filling valve at the top of the evaporator or the angle valve at the bottom;
After the unit runs stably, observe the opening of the electronic expansion valve;
If the opening of the electronic expansion valve is 40~60%, and there are always bubbles in the sight glass, add liquid refrigerant;
H, pumping refrigerant
requires attention! Do not use the compressor to pump refrigerant from the evaporator, because when the suction pressure is less than 1kg, it may damage the compressor. Use a refrigerant pumping device to pump refrigerant.
（1） Replace the built-in oil filter
When the unit runs for 500 hours for the first time, the oil filter of the compressor should be checked. After every 2000 hours of operation, this article comes from Refrigeration Encyclopedia, or when the pressure difference between the front and rear of the oil filter is found to exceed 2.1bar, the oil filter should be disassembled and checked.
（2）When the following two situations occur, the pressure drop of the oil filter should be checked:
The compressor shuts down due to the alarm of ‘maximum oil pressure difference in the oil supply circuit’;
Compressor shuts down due to ‘Oil level switch disconnected’ alarm.
J. Oil filter replacement process
Shut down, pull the compressor air switch off, close the oil filter maintenance angle valve, connect a hose through the oil filter maintenance hole, drain the oil in the oil filter, open the oil filter plug, and pull out the old one Oil filter, wet ‘O’ ring with oil, install new oil filter, replace with new plug, replace auxiliary oil filter (external oil filter), drain oil filter through filter service port and To aid air in the oil filter, open the oil filter service valve.
K, oil level switch disconnected
If the unit repeatedly alarms because the oil level switch is disconnected, it means that the oil in the oil separator is insufficient and a large amount of oil is in the evaporator. If the oil level switch is always disconnected, use the oil pump to add more than two liters of oil to the oil separator, do not add oil in any other position, confirm that the oil level switch is closed, restart the unit, and run at 100% load for at least 1 hour under normal conditions.
L. Running oil
Reasons for running oil: low exhaust superheat degree leads to poor oil separation effect, and the saturated exhaust temperature of the unit is too low (cooling water temperature is low), resulting in low oil pressure difference, which makes oil supply circulation difficult. Install a three-way valve on the condenser water pipeline, and adjust the PID parameters of the three-way valve controller correctly to prevent the control from oscillating.
When the excess oil enters the evaporator and mixes with the refrigerant, a large amount of foam will be generated. The control system will be able to detect this situation and make a correct response. When the foam is generated, the heat transfer temperature difference in the evaporator will increase and expand. The valve will open wide, allowing more refrigerant to enter the evaporator, increasing the refrigerant level, so that the oil is sucked away by the compressor and returned to the oil.
Post time: Jul-14-2022
