How to Perform Pressure Testing, Leak Detection and Blockage Inspection on Refrigeration Equipment?

2025-03-31

During the repair of a refrigeration system, whether it is due to refrigerant leakage or the replacement of components in the refrigeration system caused by other malfunctions, the system and soldered joints need to be pressure - tested, pressure - maintained, leak - detected, and blockage - inspected.

I. Pressure Testing

The pressure - testing methods for air conditioners mainly include nitrogen pressure - testing and refrigerant pressure - testing. Since neither nitrogen nor refrigerants contain moisture, they are non - flammable and non - corrosive. When used, they have a good drying effect on the system and are relatively safe. If air is used for pressure - testing, due to the high moisture content in the air, after the air enters the system, a layer of water dew will form on the inner wall of the pipeline, affecting the normal operation of the air conditioner (causing ice blockage).

Nitrogen Pressure - Testing
The pressure inside a nitrogen cylinder is very high. When using it, a pressure regulator needs to be connected. The outlet of the pressure regulator is connected to a pressure - resistant rubber hose, and the other end of the hose is connected to a three - way repair valve. The three - way repair valve is connected to the three - way stop valve of the air conditioner. After all the connection pipes are properly connected, open the nitrogen cylinder valve. While adjusting the manual adjustment rod of the pressure regulator (clockwise), observe the reading on the pressure - reducing gauge. When the reading reaches 1MPa, open the three - way repair valve to allow nitrogen to enter the refrigeration system. When the pressure gauge reading on the three - way repair valve reaches 1.2MPa, close the three - way repair valve. Finally, close the nitrogen cylinder valve and turn the manual adjustment rod of the pressure regulator counter - clockwise back to its original position. Remove the connection pipes, and the pressure - testing is completed. When an air conditioner is pressure - tested with nitrogen, the charged pressure generally should not exceed 1 - 1.2MPa (10 - 12kgf/cm²).
Refrigerant Pressure - Testing
Refrigerant pressure - testing has a good leak - detection effect, but it is costly. The operation method for pressure - testing is the same as that for nitrogen pressure - testing. When using refrigerant for pressure - testing, the charged pressure generally should not exceed 0.2 - 0.4MPa (2 - 4kgf/cm²).

II. Leak Detection

Phenomena and Causes of Refrigerant Leakage and Low Refrigerant Level
Low refrigerant level is caused by leakage and is a common malfunction in air conditioners and refrigerators. The methods for judging low refrigerant level, preventive measures, and repair operations are important professional skills for maintenance personnel and also a practical issue that air conditioner and refrigerator users generally pay attention to.
After the compressor of an air conditioner has been running continuously for 30 minutes, if the refrigeration system has a low refrigerant level, the following phenomena will occur.
(1) The gas pipe valve is dry, and there is no obvious cool feeling when touched by hand.
The reason is that insufficient refrigerant causes the boiling end - point in the evaporator to advance, increasing the refrigerant superheat degree of the valve, raising the valve temperature, and making it higher than the dew - point temperature of the outdoor air.
(2) The liquid pipe valve is frosted.
The reason is that the low refrigerant level leads to a drop in pressure in the liquid pipe and a decrease in the boiling point, making the valve temperature lower than the freezing point.
(3) Open the panel of the indoor unit and remove the filter screen. It can be found that only part of the evaporator is dewed or frosted.
The reason is that due to insufficient refrigerant, only part of the evaporator undergoes boiling and heat absorption, reducing the refrigeration area accordingly.
(4) The exhaust from the outdoor unit has no heat feeling.
The reason is that insufficient refrigerant causes a decrease in both the condensing pressure and condensing temperature, and the exhaust humidity also decreases.
(5) The drainage hose drains intermittently or does not drain at all.
The reason is that the refrigeration area of the evaporator decreases, the dewing area also decreases, and the amount of condensed water is reduced.
(6) There is oil stain on the gas and liquid valves of the outdoor unit. If there is oil stain, there is leakage.
The reason is that the refrigerant and the refrigeration oil are somewhat miscible. After the fluorine escapes from the leak point into the atmosphere, the oil adheres around the leak point.
(7) The measured operating current of the air conditioner is less than the rated current.
The reason is that insufficient refrigerant reduces the working load of the compressor, causing the current to drop.
(8) The pressure measured from the refrigerant - charging port of the outdoor unit is lower than 0.45MPa.
The reason is that insufficient refrigerant leads to a drop in the evaporation pressure. In addition, frosting on any valve of the outdoor unit is an abnormal phenomenon. If only the liquid pipe valve is frosted, it indicates a serious low - refrigerant situation. If only the gas pipe valve is frosted, it indicates a slightly low - refrigerant situation or a low ambient temperature. If both valves are frosted, it indicates a secondary throttling phenomenon in the system.
There are many methods for leak detection. One or more methods should be determined according to the specific situation and conditions to find the leak point conveniently, quickly, and accurately.
Main parts for leak detection: The welded joints of the suction and discharge pipes of the compressor; the small elbows, inlet and outlet pipes, and welding parts of each branch pipe of the evaporator and condenser, such as the connections of the dryer, stop valves, electromagnetic four - way valves, distributors, liquid receivers, etc.
Visual Inspection for Leak Detection
When there is a leakage of R22, the refrigeration oil will also seep out or drip. By using this characteristic, we can judge whether there is a leakage at a certain place by visually checking or touching for the presence of oil stains.

When the leakage is minor and not obvious to the touch, you can wear white gloves or use white paper to touch the suspicious areas, and the leakage point can still be detected.
When an oil stain is found at a certain part of the refrigeration system, this part may be a leakage point. Visual inspection for leak detection is simple and cost - free, but it has significant drawbacks. Unless there is a large - scale break in the system and the leaked medium in the system is a liquid and colored, visual inspection cannot accurately locate the leak point. This is because the leakage points are usually very small, and many parts of the air conditioner are hardly visible.
3. Leak Detection with Dishwashing Detergent Solution or Soapy Water
The dishwashing detergent solution used in the kitchen can be slightly diluted with water to become a leak - detection solution for air - conditioner pipelines.
Soapy water can also be used as a leak - detection solution. Cut soap into thin slices, soak them in hot water, and keep stirring until they dissolve. After the soapy water cools and solidifies into a thick, light - yellow solution, it can be used.
When leak - detecting, dip a small brush or finger into the dishwashing detergent solution or soapy water and apply it to various parts of the system to be inspected, and observe carefully. If white foam appears at the inspected part or if bubbles keep growing, it indicates that there is a leakage.
The method of leak detection with dishwashing detergent solution or soapy water is simple and easy to perform. Generally, maintenance personnel often use this method for leak detection.
4. Leak Detection with Nitrogen and Water
This method is often used for leak detection of components such as compressors (note that the terminal connections should be protected from water), evaporators, and condensers. The method is as follows: For the evaporator, charge 0.8MPa of nitrogen; for the condenser, charge 1.9MPa of nitrogen (for heat - pump - type air conditioners, both should be charged with 1.9MPa of nitrogen), and then immerse them in warm water at about 50°C and observe carefully for bubbles. The purpose of using warm water is to reduce the surface tension of water. Because the lower the temperature of water, the greater the surface tension, and small leaks may not be detected.
The leak - detection site should have sufficient light and a calm water surface. The observation time should be no less than 30 seconds, and the workpiece is preferably immersed more than 20 cm below the water surface.
It should be noted that the water used for leak detection is likely to enter the system, causing corrosion to the materials in the system. At the same time, high - pressure gas may also cause greater damage to the system. The components after immersion leak - detection should be dried before repair welding.
5. Electronic Leak Detection
Move the probe of the electronic leak - detection device towards the areas where leakage is possible. When the leak - detection device alarms, it indicates that there is a large - scale leakage at this point.
6. Fluorescent Leak Detection
Fluorescent leak detection is based on the principle that a fluorescent leak - detection agent emits bright yellow - green light under the irradiation of an ultraviolet leak - detection lamp to detect refrigerant leakage in the refrigeration system. When using it, simply add the fluorescent agent to the system in a certain proportion. After the system runs for 20 minutes, put on special glasses and use the leak - detection lamp to irradiate the outside of the system. The leakage point will show yellow fluorescence. The advantages of fluorescent leak detection are accurate positioning, the leakage point can be directly seen with the naked eye, and it is easy to use and convenient to carry.
7. Leak Detection by Pressurization
After the refrigeration system has been repaired and welded, before charging the refrigerant, charge 1.5MPa of nitrogen and close the three - way maintenance valve (the valve itself should not leak). If the gauge pressure does not drop after 12 hours, it indicates that the repaired refrigeration system has no leaks. If the gauge pressure drops, it indicates that there is a leakage, and then use the soapy - water leak - detection method for further detection.

III. Blockage Inspection

Common fault phenomena of capillaries include dirt blockage, ice blockage, and wax deposition, etc. Common fault phenomena of dryer filters include dirt blockage and ice blockage, etc.

Dirt Blockage of the Capillary Tube
Inspection and judgment of dirt blockage of the capillary tube:
(1) Install a three - way maintenance valve on the liquid - charging process tube of the compressor.
(2) Start the compressor and let it run for a while. If the low pressure remains at 0Pa all the time, it indicates that the capillary tube may be in a semi - dirt - blocked state.
If it is in a vacuum state, it may be completely blocked, and further inspection is required. At this time, the compressor runs with a dull sound.
(3) After stopping the compressor, if the pressure balance is very slow, taking ten minutes or even half an hour or more, it indicates that the capillary tube is dirt - blocked. The dirt - blocked position is usually at the joint between the dryer filter and the capillary tube. If the connection between the capillary tube and the dryer filter is cut and the refrigerant sprays out, it can be judged that the capillary tube is dirt - blocked.
Tips: What should be done if there is no capillary tube with the same inner diameter and length when the capillary tube is dirt - blocked?
(1) The dirt can be burned and melted by annealing, and then pressurized and blown to make it unobstructed.
(2) The capillary tube can also be welded into a clean pipeline and flushed with gasoline or carbon tetrachloride. The capillary tube after flushing must be vacuum - dried before use.
Ice Blockage of the Capillary Tube
(1) Inspection and judgment of ice blockage of the capillary tube.
Ice blockage of the capillary tube mostly occurs in repaired or under - repair systems, mostly due to poor vacuum treatment of the refrigeration system, excessive water content in the system, or excessive water content in the refrigerant itself.

Ice blockage mostly occurs at the outlet end of the capillary tube. When the liquid refrigerant evaporates from the capillary tube into the evaporator, its volume expands greatly and turns into gas, absorbing a large amount of heat. At this time, the evaporation temperature can reach about -5°C. The trace amount of water in the system freezes into ice when it circulates to the outlet end of the capillary tube along with the refrigerant. As the refrigerant continues to circulate, the volume of the formed ice gradually increases, and to a certain extent, it will completely block the capillary tube.
Judgment method: Connect the power supply. After the compressor starts running, the evaporator frosts and the condenser heats up. As the "ice blockage" forms, all the frost on the evaporator melts, the compressor runs with a dull sound, and no cold air is blown into the room. After shutting down, wrap the inlet of the capillary tube into the evaporator with a hot towel several times. Since the ice - blocked part melts, the flowing sound of the refrigerant in the unobstructed pipeline can be heard. After starting the compressor, the evaporator starts to frost again. After the compressor runs for a while, the above - mentioned situation will occur again, which can be judged as ice blockage of the capillary tube.
(2) Removal of ice blockage in the capillary tube
After determining that the capillary tube is ice - blocked, first release the refrigerant in the refrigeration system and perform vacuum drying treatment again. Clean the main components of the refrigeration system, namely the evaporator and the condenser.
When reconnecting the refrigeration system, replace the dryer filter with a new one. If there is no new dryer filter, pour out the molecular sieve inside the removed dryer filter, flush the inner wall of the filter with gasoline or carbon tetrachloride, and use it after drying treatment.
If the ice blockage is caused by excessive water content in the refrigerant itself, a dryer filter can be added at the outlet of the refrigerant cylinder so that the water is absorbed when the refrigerant is charged.
Although oil blockage and ice blockage both show a significant drop in the low - pressure suction pressure of the compressor, there are still some differences. When the refrigeration system is oil - blocked, it is mostly in a semi - blocked state, and the refrigerant flow is not smooth. Generally, the periodic frosting and defrosting phenomena that occur during ice blockage will not appear.

How to Perform Pressure Testing, Leak Detection and Blockage Inspection on Refrigeration Equipment?1743379803856

When switching to the heating mode, the electromagnetic reversing valve works to change the flow direction of the refrigerant. The waxy substance in the capillary tube may be carried away in the opposite direction by the impact force at the moment of startup, and the pipeline will be temporarily unobstructed, allowing the system to heat normally.
3. Wax Deposition in the Capillary Tube
(1) Inspection and judgment of wax deposition in the capillary tube
Because R22 is miscible with the refrigeration oil, after years of circulation, R22 contains a certain proportion of refrigeration oil. The wax components in the oil precipitate at low temperatures. During the refrigeration cycle, the wax components gradually deposit on the inner wall of the outlet of the capillary tube with a very low temperature. The inner diameter of the capillary tube becomes smaller, and the flow resistance increases, resulting in a decline in refrigeration performance.
For an air conditioner that has been used for many years, if during operation, the temperature of the evaporator is on the high side, the temperature of the condenser is on the low side, and the reasons for slight refrigerant leakage and poor compressor efficiency have been ruled out, the fault is generally caused by "wax deposition" in the capillary tube.
(2) Removal of wax deposition in the capillary tube
For the repair of a wax - deposited capillary tube, a high - pressure gun can be used to remove it. Pressurize the refrigeration oil to 2MPa with a screw rod with a column to remove the wax deposition. It can also be replaced with a new capillary tube.
4. Dirt Blockage in the Dryer Filter
(1) Inspection and judgment of dirt blockage in the dryer filter
The "dirt blockage" of the dryer filter is caused by reasons such as poor welding in the refrigeration system, which causes the oxide skin on the inner wall of the pipe to fall off, mechanical wear caused by long - term operation of the compressor, resulting in impurities, or the refrigeration system not being cleaned thoroughly before assembly and welding. The fault phenomenon of "dirt blockage" is that the surface of the dryer filter is cold, dewed, or frosted, resulting in insufficient refrigerant supply to the evaporator or preventing the refrigerant from circulating for refrigeration.
Judgment method of dirt blockage in the dryer filter: After the compressor starts running for a while, the condenser does not heat up, no cold air is blown out, touch the dryer filter, it is cold, dewed, or frosted, and the compressor makes a dull over - load sound. To further confirm the "dirt blockage" of the dryer filter, cut the capillary tube near the dryer filter. If no refrigerant sprays out or the spraying pressure is low, it indicates "dirt blockage". At this time, if a small slit is cut in the condenser tube near the connection with the dryer filter with a pipe cutter, the refrigerant will spray out. At this time, special attention should be paid to safety to prevent the refrigerant from spraying and hurting people.
(2) Removal of dirt blockage in the dryer filter
After the dryer filter is dirt - blocked, slowly cut the connection between the condenser and the dryer filter (to prevent the refrigerant from spraying and hurting people), then cut the capillary tube and remove the dryer filter. Since it is relatively difficult to repair the dryer filter, it is generally better to replace it with a new one. Before replacing the dryer filter, it is best to clean the evaporator and the condenser.
Differential judgment between leakage and blockage: After leak - repairing the leakage point, performing vacuuming, and refilling the refrigerant, the refrigeration effect of the air conditioner can be restored. If it is a blockage, even if refrigerant is added, the air conditioner still cannot refrigerate, and the pressure is also abnormal.