Determination of the refrigerant level in the cooling circuit is a key diagnostic step when the refrigerator stops freezing, but the compressor continues to work. Many owners of household appliances mistakenly believe that it is checking freon pressure possible without opening the system, but this is not the case. To obtain accurate readings, it is necessary to connect specialized equipment directly to the line.
Reduced pressure in the system almost always indicates depressurization of the circuit and leakage of the working substance. In this case, a simple “pumping” of gas will not solve the problem for a long time, unless the place of damage to the tubes or condenser is found and eliminated. Refrigerant circulates in a closed cycle, and its quantity must remain unchanged throughout the entire service life of the unit.
Before you begin manipulating the tool, you need to understand that you are dealing with a pressurized system containing chemicals. Incorrect actions can lead to complete failure of the compressor or even explosion of the tubes if the degasser does not operate correctly. Therefore, below we will analyze in detail the diagnostic process, indicator standards and typical errors.
Necessary diagnostic tools
To carry out high-quality diagnostics of the refrigeration circuit, a conventional set of household tools will not be enough. You will need specialized equipment that allows you to not only measure the current state of the system, but also safely carry out evacuation and charging. The main device is pressure gauge station, consisting of two pressure gauges (blue and red) and a set of connecting hoses.
The blue pressure gauge (low pressure) is used to control suction and filling, and the red one (high pressure) is used to control air injection and removal. A vacuum pump is also critical to remove moisture and remaining air from the system before refilling. Without deep evacuation freon it will mix with air, which will lead to the formation of acids and rapid combustion of the compressor.
In addition, you will need scales for accurate dosing of the refrigerant, since filling “by eye” or only by pressure often leads to errors. To search for leaks, a leak detector or a solution with soap foam is used, and to connect to the pipe, a service valve (shredder valve) and a torch for soldering copper or steel pipes are used.
⚠️ Attention: The use of automobile pressure gauges or homemade devices is strictly prohibited. The pressure scale in refrigeration systems is measured in bars (or PSI), and the scale of division of household appliances is too high for precise adjustment of the refrigerator.
Preparing the refrigerator for measurements
Before connecting pressure gauges, it is necessary to prepare the unit itself and ensure safe access to the process tube. First of all, the refrigerator must be disconnected from the power supply and defrosted. The presence of ice in the evaporator can distort the readings, since ice blocks heat transfer, creating a false impression of a lack of freon.
Locate the process tube on the compressor. This is usually a short piece of tubing, sealed at the end, located next to the main body of the motor. It is through it that the system is maintained. If there is already a valve on the tube, make sure that it is working properly and does not leak gas. In most cases, it is necessary to cut off the tip of the tube and solder in a new service valve.
After installing the valve, screw the hose from the blue pressure gauge onto it. After connecting the hose, the valve is opened, and the pressure gauge arrow will show residual pressure in the system. If the arrow is at zero, it means that the freon has completely evaporated, and a vacuum or atmospheric pressure has formed in the system.
☑️ Preparation for diagnostics
Normal pressure readings for different refrigerants
One of the most common mistakes made by technicians is trying to focus only on pressure when filling. The pressure in the system directly depends on the ambient temperature and the temperature inside the evaporator. However, there are average values that can be relied upon when initially diagnosing the health of the circuit.
Modern refrigerators most often operate on isobutane (R600a) or freon R134a. These gases have different physical properties and operating pressures. Isobutane is a flammable gas, so its refilling requires special care and the absence of open flames indoors. Its pressure is lower than that of R134a, which often confuses inexperienced repairmen.
Below is a table of approximate suction pressure values at an ambient temperature of +25°C. This data is relevant for a healthy system in the operating cycle.
| Refrigerant type | Suction pressure (bar) | Suction pressure (PSI) | Features |
|---|---|---|---|
| R134a | 0.07 – 0.10 | 1.0 – 1.5 | Non-toxic, requires synthetic oil |
| R600a (Isobutane) | 0.03 – 0.06 | 0.5 – 0.9 | Explosive, small filling (up to 60 g) |
| R12 (Obsolete) | 0.08 – 0.12 | 1.2 – 1.8 | Used before 2000, prohibited |
It is important to understand that nominal pressure is not a static figure. When the compressor starts, the suction pressure will drop, creating a vacuum, and when it stops, it will equalize. Therefore, diagnostics are carried out dynamically, observing the behavior of the pressure gauge needle over several minutes of engine operation.
Why can the pressure be higher than normal?
If the suction pressure is higher than that indicated in the table, this may indicate several problems: 1. An excess of freon in the system. 2. Thermostat malfunction (the compressor does not turn off). 3. Air entering the circuit due to improper filling. 4. Low efficiency of the compressor (wear of valves), which does not have time to pump gas out of the evaporator.
Testing algorithm and leak detection
The testing process begins by connecting a pressure gauge to the service valve. If the pressure gauge shows zero, this does not mean that a hole has been found. The system could simply be bleeding gas slowly over months. To find a leak, the system must be pressurized with nitrogen. The use of oxygen or compressed air from the compressor is prohibited due to the risk of explosion and moisture ingress.
After introducing nitrogen into the system at a pressure of 6-10 bar (for R600a) or 10-15 bar (for R134a), listen carefully. A characteristic whistle will indicate the location of depressurization. If you cannot determine it by ear, use a soap solution. Apply it with a brush to all suspicious areas: welds, solder joints, the evaporator inside the chamber (if accessible) and the condenser at the back.
Looking for leaks - the process is painstaking. Gas often escapes through microcracks in the foamed part of the housing, in places where the tubes enter the insulation. In such cases, the soap suds may swell very slowly. Professionals use electronic leak detectors that react to gas molecules in the air, or an ultraviolet additive in the compressor oil.
⚠️ Attention: Never check for leaks with an open flame! Freon R600a (isobutane), used in most modern refrigerators, is a flammable gas. A spark from a burner or lighter in the leak area can cause a powerful bang or fire.
If the leak is found in an accessible place (for example, on the back of the condenser), the tube is sealed. If the damage is in the foamed evaporator inside the case, it is often cheaper and more reliable to install an external evaporator (“crying” circuit) than to open the case and change the foamed part.
The process of vacuuming and filling the system
After eliminating the leak, the most critical stage begins - removing air and moisture. Moisture in the system is the main enemy. When passing through the capillary tube, the water freezes, forming an ice plug that blocks the circulation of freon. This phenomenon is called “hydraulic hammer” or simply “clogged capillary.”
To remove moisture, a vacuum pump is connected to the system. The pumping process should last at least 15-20 minutes, and for large systems or with heavy humidification - up to 40 minutes. The pressure gauge needle should go into the negative zone (vacuum). After stopping the pump, you need to close the valve and wait 10-15 minutes. If the arrow remains in the vacuum position, the system is sealed. If the arrow creeps up to zero, there is poor-quality soldering left somewhere.
Filling with refrigerant is carried out strictly by weight. The nameplate of the refrigerator (usually inside the chamber or on the back) indicates the exact number of grams. Dispenser or scales are required. Filling with gas “according to pressure” can only be done as a last resort and only by experienced craftsmen who adjust the amount of refrigerant, looking at the compressor consumption current and the evaporator temperature.
Typical errors and signs of malfunction
Unqualified diagnostics often lead to the fact that the refrigerator after repair works worse than before. One of the main mistakes is ignoring the cleanliness of the system. Dust or metal shavings from soldering that get inside quickly clog the filter drier and capillary tube.
Another common problem is freon. If the refrigerator is underfilled, it will work non-stop, trying to gain temperature, which will lead to overheating of the compressor. When overfilling, liquid freon can enter the compressor, causing water hammer, or the discharge pressure will become critical, which is also dangerous for the motor. underfilling or overfilling Freon. If the refrigerator is underfilled, it will work non-stop, trying to gain temperature, which will lead to overheating of the compressor. If there is an overflow, liquid freon may enter the compressor, causing water hammer, or the discharge pressure will become critical, which is also dangerous for the engine.
It is also worth mentioning the error of replacing the filter drier. Many “masters” simply solder the old filter, believing that it lasts forever. This is not true. The filter drier is a disposable element that absorbs moisture and oil breakdown products. Its replacement is required for any opening of the circuit.
⚠️ Attention: Compressor characteristics and refueling requirements may vary depending on the specific model and year of manufacture. Always check the manufacturer's technical documentation before starting work.
Frequently asked questions (FAQ)
Is it possible to check the freon level without a pressure gauge?
It is impossible to accurately determine the amount of freon without a pressure gauge station. Indirectly, a lack of gas can be indicated by weak heating of the condenser (grid at the back) only in the upper part, while the lower part remains cold. However, this method does not provide accurate data on the pressure and amount of gas.
Why does the refrigerator freeze after refueling, but after a week it stops?
Most likely, there was an unrepaired leak in the system, or the soldering technology was broken. The cause may also be frozen moisture in the capillary tube if poor-quality evacuation was carried out. In this case, repeated diagnostics and overhaul of the system are required.
Is it dangerous to breathe freon vapors?
Most modern refrigerants (R134a, R600a) are not toxic in small quantities, but they displace oxygen. In a confined space, high concentrations of gas can cause suffocation. In addition, upon contact with an open flame, freon decomposes to form phosgene gas. You need to work in a ventilated area.
Can I use freon from an old cylinder?
You can only use the refrigerant if you are sure of its purity and type. If the cylinder was opened and left for a long time, air and moisture could get inside. Filling with such gas will damage the compressor. Always use gas from proven sources with a guarantee of purity.