Methods of Vacuuming, Leak Detection, Refrigerant Recovery and Charging for the Refrigeration System of a Cold Storage

2025-04-16

I. Vacuuming of the Refrigeration System:
Vacuuming the refrigeration system is to remove the non-condensable gases and water vapor within the system. It is also an extremely important procedure before charging the refrigerant into the refrigeration system and after completing maintenance. Because when the refrigeration system is disassembled, repaired, or components are replaced, the system will communicate with the atmospheric environment, and water vapor (moist air) in the atmosphere will also enter the refrigeration system. Therefore, before charging the refrigerant after qualified installation and after the system is restored after maintenance, the system must be vacuumed to check the airtightness of the system and reach the specified vacuum standard.
For medium-sized, large-sized, and above refrigeration systems, except for the refrigeration systems of screw-type, scroll-type, centrifugal-type, and other types of refrigerators, a separate vacuum pump should be used for vacuuming; for other types of refrigeration compressor systems, the system can be vacuumed by running the machine itself.

Methods of Vacuuming, Leak Detection, Refrigerant Recovery and Charging for the Refrigeration System of a Cold Storage1744811020580

For the vacuuming of small-sized and below refrigeration systems, a vacuum pump can be used (the systems of reciprocating and rotary compressors can also directly use the machine itself for vacuuming).
Close all the valves of the refrigeration system that lead to the atmosphere, and all other valves of the system should be opened, then the vacuum operation of the system can be carried out.
Using a vacuum pump for vacuuming: 1) Connect the two high and low-pressure hoses on the manifold gauge valve group to the high and low-pressure interfaces of the compressor respectively; connect the middle hose on the manifold gauge valve group to the vacuum pump. 2) Open the high and low-pressure manual valves of the manifold gauge valve group, start the vacuum pump, and pump the vacuum of the system to 98.70—99.99kPa (760mmHg). 3) Close the high and low-pressure manual valves of the manifold gauge valve group, and carefully observe whether the indication of the pressure gauge will rise. If the pressure rises, it indicates that there is still a leak in the system, and the leak detection and repair should be carried out again. After the repair is completed, the vacuum operation needs to be carried out again, and the vacuum degree needs to remain unchanged for 24 hours before the vacuum of the system can be considered qualified.
II. Leak Detection of the Refrigeration System:
Use pressure leak detection (compressed air is prohibited in the fluorine system). Fill the refrigeration system with nitrogen at a pressure equal to that during normal operation, and then brush soapy water on all joints, welding points, flanges, valves, and other parts of the entire system, and observe carefully without missing any part. If there is a leak, mark it. After all the joints of the entire system have been strictly checked, quickly release the pressure from the blowdown port or the lowest point of the system, and then repair the marked leak points. After the repair is completed, the pressure should be increased again for leak detection until there are no leak points in the entire system.
For the leak detection of the system, it can be carried out simultaneously with the pressure test and blowdown. The pressure charged during leak detection can also be used as a pressure test for the system, and the pressure release (relief) after the test can be regarded as the blowdown of the system. This not only reduces the operation steps and procedures but also saves nitrogen and operation time, killing three birds with one stone.
When the system is already in operation and there is refrigerant in the system for leak detection, it is called the daily inspection of the system. When a leak point is found, except that the leak can be eliminated with pressure fastening, the refrigerant should be recovered according to the actual part in other cases. For the refrigerant that cannot be recovered, it should be discharged reasonably based on the principles of safety and no pollution. After the pressure is completely released, the leak point should be repaired. After the repair is qualified, the part should be vacuumed, and the system should be restored after the vacuum standard is met.
III. Refrigerant Recovery:

Recover the refrigeration working medium of the entire system to the liquid receiver of the system (if there is no liquid receiver, recover it to the condenser). First, short-circuit the low-pressure control circuit of the pressure controller, close the liquid outlet valve (liquid supply valve) at the bottom of the liquid receiver or condenser, start the compressor to operate. When the pressure of the low-pressure gauge stabilizes at 0 or slightly below, close the exhaust valve of the compressor (or the liquid inlet valve on the liquid receiver, and just close the inlet and outlet shut-off valves on the condenser if available), and the refrigerant recovery is completed.
Partial recovery of the system This refers to the recovery of the refrigerant only for a certain part of the system. It is mainly for parts or devices such as the evaporator, filter, solenoid valve, and throttle valve. Just close the liquid outlet valve on the liquid receiver (condenser) and the intake (or liquid inlet) valve of the container that needs to be recovered; start the compressor to operate. When the pressure of the low-pressure gauge stabilizes at 0 or slightly below, close the exhaust valve of the compressor (or the liquid inlet valve on the liquid receiver), and the refrigerant recovery is completed. All devices (filters, solenoid valves, throttle valves, etc.) after the liquid outlet valve of the liquid receiver in the system can be disassembled, repaired, or replaced.
External recovery (transfer) of the refrigerant of the entire system
Short-circuit the low-pressure control circuit of the pressure controller, and connect the multi-purpose port of the multi-purpose valve (bypass valve) of the compressor exhaust to an empty refrigerant cylinder. Pay attention to selecting the appropriate pressure and temperature resistance grade of the connecting pipe. The capacity of the refrigerant cylinder must be 20% or more of the total refrigerant storage capacity of the entire system. Place the empty refrigerant cylinder upright in a water tank and spray cooling water from the top of the cylinder with a water pipe (the recovery cylinder of a small system can be immersed in a corresponding water basin). Open the cylinder valve, close the multi-purpose valve of the compressor exhaust, and start the compressor to operate. The compressed high-temperature and high-pressure refrigerant gas will start to be filled into the empty cylinder. Due to the cooling of the cooling water, the high-temperature and high-pressure refrigerant vapor in the cylinder will slowly condense into a high-pressure liquid, and the refrigerant in the system will be recovered outward in this way. When the low-pressure stabilizes at 0 or slightly below, close the multi-purpose valve of the compressor exhaust, complete the refrigerant recovery, and remove the recovery connecting pipe.
There is a large amount of refrigerant in a large system, and one cylinder may not be able to hold it. The machine can be paused to change the cylinder halfway, just pay attention to safety during the operation.
IV. Refrigerant Charging:
Charging after the entire system is vacuumed After the system is vacuumed, it can be carried out first by using the pressure difference. Connect the refrigerant cylinder to the low-pressure side of the system, and pay attention to exhausting the air in the connecting pipe during the connection. The refrigerant cylinder can be placed horizontally, tilted downward, or inverted. Open the valves on both sides fully and charge quickly until the pressures on both sides are balanced.
Start the refrigerator to charge the refrigerant After the pressures of the system and the refrigerant cylinder are balanced, the refrigerant in the cylinder will no longer be charged into the system. At this time, the refrigerator needs to be started, the liquid outlet valve of the liquid receiver (condenser) should be closed, and the refrigerator should be started to charge the refrigerant just like connecting to the load of the system as usual. After the refrigerant in the system reaches the specified amount, close the cylinder valve, open the liquid outlet valve (liquid supply valve) of the system, remove the charging device, and restore the operation of the system.
Supplementary charging when the refrigerant in the system is insufficient Due to reasons such as leakage or maintenance, the refrigerant in the system is insufficient, and after the repair is qualified, the system needs to be supplemented with refrigerant. This method and operation are basically the same as point 2 of refrigerant charging. An experienced master does not need to close the liquid supply valve. Just appropriately close the suction valve (low-pressure valve) of the compressor a little.
Finally, the charging amount of the refrigerant should be basically close to the corresponding pressure of the evaporation temperature at the current refrigeration temperature.