When the refrigerator stops freezing and diagnostics indicate a refrigerant leak, the technician often says the phrase: “Crimping is needed.” For the average user, this term sounds mysterious and even scary. It seems that we are talking about some kind of complex chemical reaction or a complete replacement of the insides of the unit. In fact, pressure testing is a fundamental step in checking the tightness of the system, without which high-quality repairs are impossible.
The essence of the process is to create excess pressure inside the closed circuit of the refrigerator. This makes it possible to identify even microscopic fistulas and cracks that are invisible to the eye. If you ignore this stage and simply fill the equipment with freon, the gas will evaporate again in a week or month, leaving you with spoiled products and wasted money.
In this article we will analyze in detail the physics of the process, the gases used and the sequence of actions of the master. You will understand why high-quality pressure testing takes more time than refrigerant charging itself, and how to distinguish a conscientious specialist from one who is trying to save on your time.
The essence of the process and the physics of the phenomenon
Crimping a refrigerator is a technique for monitoring the integrity of pipelines, evaporator and condenser by pumping inert gas into them under high pressure. The physical principle is simple: if there is a hole in the system, gas under pressure will begin to escape. The technician’s task is to record a drop in pressure or detect a gas outlet using a leak detector or soap solution.
Why can’t you use air from a compressor for this purpose? The fact is that atmospheric air contains moisture. Even a small amount of water vapor that gets inside Freon pipeswill turn into ice crystals at low temperatures. These crystals can completely clog the capillary tube, which will lead to a stop in the circulation of the refrigerant.
In addition, oxygen in combination with oil and freon when heating the compressor can cause oxidative reactions leading to the formation of acids. Acids destroy motor windings and internal parts. Therefore, for crimping, only nitrogen or special mixtures are used that are chemically inert and do not contain moisture.
⚠️ Attention: Never agree to crimping with air from a compressor, even if the master claims that “they have always done it this way.” Modern refrigerants (R600a, R134a) are extremely demanding on the cleanliness of the system, and moisture will completely damage the equipment.
The pressure during pressure testing is created significantly higher than the working one. If freon moves in the circulation system under pressure from 2 to 6 atmospheres (depending on the type of gas), then to check the system is loaded to 10–15 atmospheres. This creates extreme conditions under which weak points, such as microcracks in soldering or thinned metal, immediately make themselves felt.
Why is crimp testing needed and when is it required?
Many equipment owners mistakenly believe that pressure testing is only needed when there is visible damage to the tubes. However tightness of the circuit may be violated for many hidden reasons. The main goal of the procedure is to find a leak that cannot be detected visually. Without this stage, any refilling with freon will become a temporary measure.
The procedure becomes mandatory in the following situations:
- 🔍 Mechanical breakdown of the evaporator tube was detected during defrosting with a knife.
- 🔍 The compressor or filter-drier has been replaced.
- 🔍 There is a constant leak of freon, although there is no visible damage.
- 🔍 After a long period of equipment downtime without operation.
Particular attention is paid to the system No Frost. In such models, the evaporator is hidden behind a plastic panel, and it is impossible to see corrosion or a fistula there without disassembling. Pressure testing allows you to understand whether the hidden circuit is intact, or whether a complex replacement of the evaporator will be required. The foam circuit is also checked, although finding a leak in the body of the refrigerator is much more difficult.
If you skip this step, you risk encountering a situation where the refrigerator works for a couple of days and then stops cooling again. The technician will leave, and you will have to pay for a repeat call and a new portion of expensive refrigerant. High-quality leak diagnostics saves the budget in the long run.
Gas and equipment used
Specialized equipment is used to carry out a quality check. The main tool is a nitrogen cylinder equipped with a reducer. Nitrogen is not chosen by chance: it is an inert gas, it does not burn, does not explode and does not react with oil or metal. Unlike oxygen, it is safe when in contact with compressor oil even under high pressure.
The second important element is the pressure gauge station (manifold). It consists of two pressure gauges (blue for low pressure and red for high) and hoses. Using pressure gauges the master controls the pressure build-up and monitors its drop over time. The accuracy of the instruments here is critical, since a drop of even 0.1 atmospheres may indicate a microfistula.
To find the location of the gas outlet, the following are used:
- 💧 Soap solution (bubbles show the exact location of the leak).
- 💧 Electronic leak detector (reacts to freon vapors, if any remains).
- 💧 Water (immersing components, for example, a condenser, in a bath to search for bubbles).
Sometimes, in rare cases, when there is no nitrogen at hand, some craftsmen use compressed air passed through special filter driers. However, this is considered a compromise. Ideal pressure testing scheme always implies the use of pure nitrogen of technical purity.
| Parameter | Nitrogen | Compressed air | Oxygen |
|---|---|---|---|
| Chemical activity | Inert | Contains oxygen | Oxidizing agent |
| Moisture | Absent | Requires drying | Absent |
| Safe with oil | Safe | Risk of oxidation | Explosive |
| Cost | High | Low | Average |
⚠️ Attention: It is strictly forbidden to use pure oxygen for pressure testing refrigeration systems! When oxygen comes into contact with compressor oil under pressure, an instant chemical reaction occurs, which can lead to an explosion of the compressor.
Step-by-step work technology
The process of checking leaks is a sequence of actions that requires care. First, the technician removes the old refrigerant if it still remains in the system. Then the process pipes are cut off, and a service fitting (shut-off needle) is welded or soldered to them, through which gas will be supplied.
Next follows the pumping procedure itself. The gas is supplied slowly so as not to damage weak connections with a sudden surge in pressure. Typically, the system is loaded up to 10-12 atmospheres for household refrigerators and up to 15-18 for industrial or c R134asystems. After the pressure has built up, the valve on the cylinder is closed and the hose is disconnected.
Control is carried out in two stages:
- Initial inspection of soldering points and connections using a soap solution immediately after pumping.
- Leaving the pressure gauge on the system for a period of 4 to 24 hours for monitoring speakers.
If the pressure gauge needle remains in place after a day, the system is sealed. If the pressure drops, a leak search begins. In difficult cases, when it is not possible to visually find the fistula, the technician can use the “cut-off” method, soldering parts of the circuit separately (condenser, evaporator, compressor compartment) to understand where exactly the gas is being lost.
☑️ Checklist for proper crimping
Evacuating: a mandatory final stage
After successful pressure testing and eliminating the leaks found, the system cannot simply be taken and refueled freon. Nitrogen remains inside the pipes, which was used for testing. It must be removed. A vacuum pump is used for this. The process is called vacuuming.
Vacuuming solves two problems. The first is the removal of nitrogen and residual air. The second, and more important, is removing moisture. Moisture is in the system in the form of steam, and during normal bleeding of gas it will remain on the walls of the pipes. When creating a deep vacuum, water boils at room temperature and evaporates, going into the pump.
The process lasts at least 15–30 minutes, and ideally an hour. The technician looks at the pressure gauge: the needle should go into the “green zone” (negative value). If, after turning off the pump, the pressure in the system begins to rise rapidly, it means that the tightness is broken or there is a lot of moisture in the system that evaporates. In this case, the procedure is repeated, sometimes with heating the compressor with a hairdryer for better evaporation of water.
Why can’t you pass a vacuum?
If you don’t make a vacuum, the remaining nitrogen will mix with freon, increasing the pressure in the system. This will overload the compressor and cause it to break. Moisture will cause an ice plug in the capillary, and the cold will stop being produced after 10 minutes of operation.
Typical errors and risks during repairs
Unskilled repairs often lead to the fact that the refrigerator after servicing works worse than before. The most common mistake is ignoring the holding time under pressure. Some “masters” pump gas, wait 10 minutes, see that the needle does not fall, and immediately start filling. This is a gross violation.
A microfistula can manifest itself only after a few hours, when the gas temperature stabilizes after pumping (when pumping, the gas heats up, the pressure increases, when it cools, it drops, which can be mistaken for a leak, or vice versa). Therefore exposure time under pressure should be at least several hours, and preferably a day.
Other common mistakes:
- ❌ Using a car compressor for inflation (produces a lot of moisture and oil).
- ❌ Lack of replacement of the filter drier (the old filter is already saturated with moisture and does not work).
- ❌ Forgetfulness and leaving the transport plug on the compressor fitting.
⚠️ Attention: If the technician offers you to “fill with freon without pressure testing, just to check,” refuse. This is a direct path to the fact that in a month you will again be left without cold, and the compressor may burn out due to working on a low-quality mixture of gases.
Cost and feasibility of repair
Crimping is not a free service. It requires the consumption of expensive nitrogen, time (often the technician must leave the refrigerator for a day or come twice) and the use of professional equipment. The cost of the work also includes diagnostics. However, compared to the cost of a new refrigerator, high-quality repairs with pressure testing are completely justified.
If during the inspection it turns out that the leak occurred in the foamed part of the case (the evaporator inside the wall), the repair becomes economically infeasible. In such cases, the technician will suggest installing an external evaporator (“crying” on the back wall) or will state the impossibility of restoration. Without pressure testing, you would not have known about it and would have spent money on a useless refill.
Questions and answers (FAQ)
How many atmospheres are needed to pressurize a household refrigerator?
Usually household systems are tested with a pressure of 10–12 atmospheres. For R134a refrigerant, the pressure can be raised to 15 atmospheres, and for R600a (isobutane) 8-10 atmospheres are often sufficient, since its operating pressure is lower. The exact values depend on the type of compressor and the manufacturer's recommendations.
Is it possible to do pressure testing yourself at home?
Theoretically, it is possible if you have a nitrogen cylinder, a reducer, pressure gauges and skills in working with a burner and copper pipes. However, purchasing equipment for a one-time repair will cost more than calling a technician. In addition, working with gas under high pressure requires compliance with safety precautions.
Why do you need to change the filter-drier after pressure testing?
The filter-drier contains zeolite or silica gel, which absorb moisture. During repairs, the system was in contact with air, and the filter could become saturated with moisture. If it is not replaced, it will no longer protect the system from water, which will lead to the formation of acids and ice jams.
How long does the pressure last in a working refrigerator?
In an ideally sealed system, the pressure created by nitrogen should be maintained indefinitely (indefinitely) if the ambient temperature does not change. Small fluctuations in the pressure gauge needle are possible due to changes in the temperature in the room (warmer during the day - the pressure is higher, colder at night - lower), but there should not be a general drop.
Is nitrogen used during pressure testing dangerous?
Nitrogen itself is inert and non-toxic (it makes up 78% of the air we breathe). However, the danger is posed by high pressure in the cylinder and in the pipe system. A sudden rupture of a pipe under a pressure of 15 atmospheres can lead to injuries, so the work must be carried out by a trained specialist.