Refrigerant recovery, vacuuming, leak detection, and refrigerant charging, learn everything at once! !

I. Refrigerant discharge

Refrigerant discharge generally refers to the direct discharge of refrigerant into the air.

When discharging, the surrounding environment must be well ventilated and cannot be close to open flames, otherwise toxic gases will be produced.

1. Close the high and low pressure manual valves on the manifold pressure gauge, and connect the high and low pressure hoses to the high and low pressure inspection valves of the compressor respectively, and place the free end of the intermediate pipe on the work cloth.

2. Slowly open the high pressure manual valve to allow the refrigerant to be discharged from the intermediate hose. The valve cannot be opened too wide, otherwise the refrigeration lubricant in the compressor will flow out with the refrigerant.

3. When the pressure gauge reading drops below 0.35MPa, slowly open the manual valve to discharge the refrigerant from both the high and low pressure sides at the same time.

4. Observe the pressure gauge reading. As the pressure drops, gradually open the high and low pressure manual valves until the readings of the high and low pressure gauges indicate zero.

II. Refrigerant recovery

There are three main methods for refrigerant recovery:

Cooling method, compression method, adsorption separation method

The recovery process will cause the refrigerant quality to be impure, so it is best to regenerate the recovered refrigerant.

1. Recovery steps:

1) Connect the manifold pressure gauge to the recovery machine and the car air conditioning system. Note that all connecting hoses must be flushed with the refrigerant of the air conditioning system before connection to remove the air in the hose.

2) Connect the recovery cylinder to the recovery machine, and also remove the air in the hose.

3) Connect the power supply, turn on the switch, and perform the recovery operation and shutdown according to the instructions.

4) Use a vacuum pump to vacuum the system.

5) Fill the recovered refrigerant that has been dried, filtered, and degreased into the recovery cylinder. Turn off the machine, cut off the power supply, and remove all connecting pipes.

2. Cooling recovery

Cool the refrigerant vapor to liquefy it. Dry ice can be used to cool and liquefy the refrigerant before recovery. This method is suitable for clean refrigerants.

The cooling method has an independent refrigeration cycle system, and the refrigerant in the recovery container is condensed into liquid in the evaporator. The refrigerant discharged from the automobile air conditioning system passes through the filter dryer to remove moisture and impurities; the lubricating oil in the refrigerant is removed through the oil separator and enters the recovery container. For occasions where the refrigerant purity requirements are not too strict, the recovered refrigerant can be refilled into the refrigeration system.

3. Compression recovery

Use the compression method to evaporate the refrigerant into liquid: the refrigerant discharged from the air conditioning system passes through the filter dryer to remove moisture and impurities. The suction pressure is regulated by the control valve. Part of the liquid refrigerant remains in the liquid storage tank. The gaseous refrigerant enters the compressor and is compressed into high-temperature and high-pressure gas. When passing through the oil separator, the refrigeration lubricating oil mixed with the refrigerant is separated and flows back to the compressor. The refrigerant enters the condenser to be cooled. Through the gas-liquid separator, the condensed liquid refrigerant flows to the recovery container. Part of the gaseous refrigerant in the recovery container will be sucked into the compressor through the capillary.

III. Vacuuming the Refrigeration System

Vacuuming is to remove the air and moisture in the refrigeration system, which is an extremely important procedure in air conditioning maintenance. Because when the refrigeration system is repaired or components are replaced, air will enter the system, and the air contains a certain amount of water vapor (humid air).

When the system is vacuumed, the longer the time is, the less residual moisture in the system. In order to maximize the extraction of air and moisture in the system, the repeated vacuuming method must be used, that is, after the first vacuuming is completed, continue to vacuum for more than 30 minutes.

Vacuuming pipeline connection method:

1) Connect the two high and low pressure hoses on the manifold pressure gauge to the high\low interfaces on the compressor respectively; connect the middle hose on the manifold pressure gauge to the vacuum pump.

2) Open the high and low pressure manual valves on the manifold pressure gauge, start the vacuum, and observe the two pressure gauges to vacuum the system to 98.70-99.99kPa.

3) Close the high and low pressure manual valves on the manifold pressure gauge and observe whether the pressure indicated by the pressure gauge rises. If it rises, it means the system is leaking, and leak detection and repair should be performed at this time. If the pressure gauge needle remains stationary, open the high and low pressure manual valves, start the vacuum pump and continue to vacuum for 15-30 minutes to stabilize the vacuum pressure gauge pointer.

4) Close the high and low pressure manual valves on the manifold pressure gauge.

5) Turn off the vacuum pump. First close the high and low pressure manual valves, and then turn off the vacuum pump to prevent air from entering the refrigeration system.

IV. Refrigeration system leak detection

1. Pressure leak detection

Add nitrogen to the refrigeration system, and then use soap solution to detect leaks. If there is a leak, soap bubbles will appear at the leak. When using pressure leak detection, it is strictly forbidden to use compressed air for leak detection, because compressed air contains moisture, and moisture will cause ice blockage at the expansion valve after entering with air. Industrial nitrogen is non-corrosive, moisture-free, and cheap, but bottled high-pressure nitrogen must be filled with a pressure reducing gauge.

When testing for leaks under pressure, first connect the manifold pressure gauge correctly: the high-pressure hose is connected to the exhaust pipe (high-pressure side), and the low-pressure hose is connected to the intake pipe (low-pressure side). Connect the hose to the high- and low-pressure inspection valves of the compressor, open the high- and low-pressure inspection valves, and add dry nitrogen to the system. The pressure should generally be around 1.5MPa. When the system reaches the specified pressure, apply soap solution to each connection and welding point of the system and carefully observe whether there is any leakage.

There will be a slight sound and large bubbles in places with large leaks, and small bubbles will appear intermittently in places with small leaks. Therefore, leak detection must be careful and checked repeatedly for 3 to 5 times. If a leak is found, it should be marked and repaired in time, and then other joints should be tested for leaks until the leak is completely eliminated. After the leak is repaired, a leak test should be conducted, and the system should be kept under pressure for 24 to 48 hours. If the pressure does not drop, the leak test is qualified. If the pressure drops significantly, the leak test must be repeated until the leak is found and eliminated.

2. Vacuum leak detection

Use a vacuum pump to perform the test. The vacuum degree should reach 0.1MPa. Keep the vacuum degree unchanged for 24 hours. Vacuuming is used to extract the residual nitrogen in the system, check whether the system has leaks, and dry the system. Refrigerant can only be added after the system is evacuated.

3. Appearance leak detection

Refrigeration lubricant oil often seeps out of the refrigerant leakage site. If oil seepage is found somewhere, it can be further wiped with clean white paper or directly touched by hand for inspection. If oil still comes out, there may be a leak.

V. Refrigerant filling

1. High-pressure end filling

The bypass hole (multi-purpose channel) of the compressor exhaust valve (high-pressure valve) is filled with refrigerant liquid. It is safe and fast, and is suitable for the first filling of the refrigeration system, that is, the filling of the system after leak detection and vacuuming. However, when using this method, you must pay attention that the compressor cannot be turned on during filling (engine stopped), and the refrigerant tank is required to be inverted.

Operation steps:

1) After the system is evacuated, close the high and low pressure manual valves on the manifold pressure gauge.

2) Connect one end of the intermediate hose to the joint of the refrigerant tank injection valve, open the refrigerant tank opening valve, and then unscrew the nut at one end of the manifold pressure gauge hose to allow the gas to overflow for a few minutes, and then tighten the nut.

3) Unscrew the high-pressure side manual valve to the full open position and turn the refrigerant tank upside down.

4) Inject the specified amount of liquid refrigerant from the high-pressure side. Close the refrigerant tank injection valve and the high-pressure manual valve on the manifold pressure gauge, and then remove the instrument. When filling the system with refrigerant from the high-pressure side, the engine is in a non-starting state (compressor stopped), and do not unscrew the low-pressure manual valve on the manifold pressure gauge to prevent hydraulic shock.

2. Filling at the low-pressure end

Filling from the bypass hole (multi-purpose channel) of the compressor suction valve (low-pressure valve) is filled with refrigerant gas. Its characteristic is that the filling speed is slow and it can be used when the system is replenishing refrigerant.

Operation steps

1) Connect the manifold pressure gauge to the compressor and the refrigeration tank.

2) Open the refrigerant tank, loosen the nut of the middle injection hose on the manifold pressure gauge until you hear the sound of refrigerant vapor flowing, and then tighten the nut. Thus, the air in the injection hose is discharged.

3) Close the manual high-pressure valve, stand the refrigerant cylinder upright, start the engine, run the air conditioning compressor, open the low-pressure manual valve, let the gaseous refrigerant enter the compressor from the low-pressure side, and when the system pressure value reaches 0.4MPa, close the low-pressure manual valve and the refrigerant tank switch valve.

4) Start the engine, turn on the air conditioning switch, and adjust the blower switch and temperature control switch to the maximum.

5) Open the manual valve on the manifold pressure gauge again to allow the refrigerant to continue to enter the refrigeration system until the filling amount reaches the specified value.

6) After filling the specified amount of refrigerant into the system, observe from the sight glass to confirm that there are no bubbles or excess refrigerant in the system. Then adjust the engine speed to 2,000r/min, and turn the cold blower air volume to the highest gear. If the temperature is 30-35℃, the low-pressure side pressure in the system should be 0.147-0.192MPa, and the high-pressure side pressure should be 1.37-1.67MPa.

7) After filling, close the low-pressure manual valve on the manifold pressure gauge, close the injection valve installed on the refrigerant tank, stop the engine, and remove the manifold pressure gauge from the compressor. When removing, move quickly to avoid excessive refrigerant leakage.

VI. Filling of refrigeration oil

Use the suction effect of the compressor itself: suck the refrigeration lubricating oil from the low-pressure valve. At this time, the compressor must keep running at a low speed.

1) Vacuum the refrigeration system

2) Select a graduated cylinder and fill it with more refrigeration lubricant than the refrigeration lubricant to be added.

3) Unscrew the low-pressure hose connected to the compressor from the manifold pressure gauge and insert it into the cylinder containing the refrigeration lubricant.

4) Start the vacuum pump and open the high-pressure manual valve on the manifold pressure gauge. The added lubricant will enter the compressor from the low-pressure side of the compressor. When the amount of refrigeration lubricant reaches the specified amount, stop the vacuum pump and close the high-pressure manual valve.

5) After filling the refrigeration lubricant according to the vacuum method, continue to vacuum the refrigeration system and add refrigerant.