A malfunction of the refrigeration unit often manifests itself in insufficient cooling of the chambers or a complete stop of the device, which forces the owner to look for the cause of the breakdown. One of the key characteristics of the health of the system is the operating pressure of the refrigerant, which is created by the compressor to circulate freon throughout the circuit. It is this parameter that allows you to accurately diagnose the condition compressor, the presence of leaks or blockage of the capillary tube without the need to disassemble the entire unit.
Checking pressure is not just a formality, but a necessary stage of deep diagnostics, which requires special equipment and an understanding of physical processes. If you notice that the refrigerator Indesit or LG began to work intermittently, hum, or has stopped freezing, measuring the parameters in the system will be the first step to identifying the true problem. Unlike checking the electrical circuit, working with pressure requires caution and compliance with safety precautions.
In this article we will analyze in detail what tools are needed to take measurements, how to correctly connect the pressure gauge station and what values are considered normal for different types of refrigerants. You will learn the difference between suction and discharge and why you cannot rely solely on the force of the jet from the service tube. Correct interpretation of instrument readings will help you make an informed decision on further actions: replacing the filter, refilling with freon or completely replacing the engine.
Necessary tools and preparation for diagnostics
To carry out high-quality diagnostics, you will need a specialized tool, without which accurate measurements are impossible. The main device is pressure gauge station (manifold), consisting of two pressure gauges: blue (for low pressure) and red (for high pressure). You also need a set of connecting hoses of the appropriate diameter and adapters for connecting to a service fitting or a bitten off pipe.
In addition to pressure gauges, you will need a pipe cutter to carefully cut through the copper tube, and a roller or torch to subsequently restore the tightness of the system. Be sure to wear gloves and safety glasses, as pressurized coolant can cause frostbite if it comes into contact with exposed areas. To seal the connections after checking, you will need solder or high-quality clamping couplings.
Before starting any work, the refrigerator must be completely disconnected from the electrical network. This is a critical safety rule that cannot be ignored. If you plan to check the pressure on a running compressor, connect to the network only after the measuring circuit has been completely assembled and all connections have been checked for leaks.
⚠️ Attention: Never measure pressure on a compressor connected to the network if the pressure gauge hoses are already connected to the system, but the valves are not open. A sudden surge in pressure when opening the valve can damage the pressure gauge or cause injury.
Make sure your tools are calibrated and the hoses are not cracked. The use of faulty equipment can lead to false readings, which ultimately leads to incorrect diagnosis and unnecessary costs for spare parts. Particular attention should be paid to the condition of the rubber seals at the ends of the manifold hoses.
Technique for connecting the pressure manifold
The process of connecting the measuring equipment depends on the design of the refrigeration unit and the presence of a service fitting. Modern models often have a special Schrader valve, similar to a car nipple, which greatly simplifies the task. If there is no such valve, you will have to make an insert into the copper tube of the process, which requires more complex manipulations.
To connect to the suction system (low pressure), a blue hose and a blue pressure gauge are used. This circuit is connected to a tube running from the evaporator to the compressor. The red hose and high pressure gauge are connected to the discharge tube coming out of the compressor, although monitoring only the low pressure is often sufficient for an initial diagnosis of leaks or performance.
- 🔧 Carefully cut the compressor process tube perpendicular to ensure a straight cut for flaring or installing an adapter.
- 🔧 Securely fix the hose to the fitting, making sure that the connection is tight and does not allow air or gas to pass through.
- 🔧 Before opening the pressure gauge valve, briefly open the hose to displace air from the hose itself.
- 🔧 Check the tightness of all connections with a soap solution before starting the compressor under pressure.
If you are working with a system where there was already a vacuum, the connection must be made as quickly as possible to minimize the entry of moisture and air into the circuit. Moisture in the system is enemy number one, as it can freeze in the capillary tube and cause an ice plug that blocks the circulation of freon.
☑️ Preparing to connect the pressure gauge
Normal pressure readings for different refrigerants
The pressure in the refrigerator system directly depends on the type of refrigerant used and the ambient temperature. It is impossible to compare the readings of a system operating on R134awith a system on R600a, since their physical properties and operating pressure are radically different. Understanding these differences is the basis for correct diagnosis.
The most common refrigerant in modern household refrigerators is isobutane (R600a). It has excellent refrigeration properties and is environmentally friendly, but operates at very low pressure, often below atmospheric pressure. This means that when the compressor is stopped, the pressure gauge may show zero or even a slight vacuum, which is absolutely normal for this gas. Freon
Freon R134a, which is often found in older models or middle-aged refrigerators, operates at a positive excess pressure even at rest. The table below will help you navigate the normal suction pressure values when the compressor is running and the ambient temperature is about 20-25°C.
| Refrigerant type | Resting pressure (bar) | Working suction pressure (bar) | Features |
|---|---|---|---|
| R600a (Isobutane) | 0 - 0.1 (often vacuum) | 0.4 - 0.6 | Flammable, requires caution |
| R134a (Tetrafluoroethane) | 3.0 - 4.0 | 0.8 - 1.2 | Non-flammable, sensitive to moisture |
| R12 (Outdated) | 4.0 - 5.0 | 1.0 - 1.5 | Found in old equipment |
A critical sign of a malfunction is a lower suction pressure 0.2 bar for R600a or higher than 1.5 bar for R134a with the compressor running. Such deviations indicate serious problems in the circuit.
Diagnostics by suction and discharge pressure
Analysis of pressure gauge readings allows you to identify a specific unit that has failed. If, when the compressor is turned on, the needle on the low pressure gauge quickly drops into a deep vacuum (below 0 bar), this indicates clogging of the capillary tube or a filter drier. In this case, freon cannot circulate, and the compressor tries to pump out the remaining gas from the evaporator.
In the case when the pressure immediately after starting becomes normal, but the refrigerator does not freeze, and the compressor works constantly, most likely it has occurred refrigerant leakage. The compressor simply circulates air or remaining gas without creating the necessary temperature difference. The pressure in such a system will tend to atmospheric or remain stably low without dynamics.
What is bypass in a compressor?
Bypass (or loss of performance) occurs when the internal valves of the compressor wear out. In this case, the motor hums, the tubes may be warm, but no pressure is created in the system - the pressure gauge needle is at zero or fluctuates in a narrow range. This requires replacing the compressor.
High pressure on the suction side (above normal) may indicate a malfunction of the compressor itself, which is not able to create sufficient vacuum, or problems with the thermostat, causing the system to operate abnormally. It may also be a sign of oil getting into the circuit or the wrong type of refrigerant being used in a previous repair.
To accurately diagnose the discharge pressure (high side), a red pressure gauge must be connected. Normally, it should be significantly higher than at suction and depend on the condensation temperature. If the high pressure is too high, this may indicate contamination of the condenser with dust or a malfunction of the blower fan.
Analysis of the compressor condition by current and pressure
Pressure is not the only parameter that needs to be taken into account. Comprehensive diagnostics necessarily include measurement of compressor consumption current. The combination of pressure gauge and ammeter readings gives a complete picture of the condition of the unit. If the pressure is low, and the current consumption is also lower than the nominal current indicated on the tag, this is almost always a leak.
If the pressure gauge shows normal or high pressure, and the current consumption significantly exceeds the rated values, this may indicate mechanical problems inside the compressor or electrical faults in the windings. Overheating of the motor in such conditions can quickly lead to its combustion or activation of the thermal protection relay.
- ⚡ The current is normal, the pressure is normal - the refrigerator is working, look for a problem in the thermostat or control.
- ⚡ The current is low, the pressure is low - freon leak, searching and soldering is necessary (places leaks).
- ⚡ High current, low pressure - possible blockage of the capillary system or malfunction of the compressor valves.
- ⚡ High current, high pressure - problems with heat exchange in the condenser or excess refrigerant.
Current measurement is carried out using current clamps, which are placed on one of the compressor power wires. This is a safe and fast way to receive data without breaking the electrical circuit. Always check the data obtained with the plate on the motor housing, where the rated current is indicated In.
Typical errors during self-checking
Self-diagnosis is often accompanied by errors that may not only not help, but also aggravate the situation. One of the most common mistakes is trying to estimate the pressure “by eye” by biting off the tube and sticking your finger in. This method is extremely inaccurate and dangerous, as it does not provide an understanding of the real pressure in the system and can lead to oil or gas getting into the eyes.
Another common mistake is ignoring the compressor operating time before measuring. The pressure does not stabilize immediately. It is necessary to let the refrigerator run for at least 10-15 minutes so that the parameters in the circuit come into balance. Measurements taken in the first minute of operation are not informative and can be misleading.
⚠️ Attention: It is strictly forbidden to check the tightness of the system with an open fire if flammable gas R600a could remain in the circuit. This may cause an explosion. Use only a soap solution or special leak detectors.
Also, novice technicians often forget to replace the filter-drier after opening the system. Even short-term contact of the internal parts of the refrigerator with atmospheric air saturates them with moisture. Without replacing the filter, this moisture will soon cause corrosion and blockage of the system, and the repair will have to be repeated.
When the help of a professional technician is needed
Despite the availability of tools, there are situations when self-repair is impractical or dangerous. If the diagnostics showed a leak in the foamed part of the housing (the evaporator inside the chamber or in the walls), to eliminate it you will need to open the casing or change the entire evaporator, which is a complex and time-consuming procedure.
Also, the help of a specialist is necessary if you do not have experience working with a blowtorch and nitrogen. Proper soldering of copper pipes requires skill so as not to burn the metal and create a new leak. In addition, to refill the refrigerator, accurate weighing of the refrigerant is required, since a deviation of even 10-20 grams can disrupt the operation of the unit.
If, after your manipulations, the refrigerator began to work, but after a short time it stopped cooling, or the compressor began to make uncharacteristic sounds (metallic knocking, clanging), immediately stop using it and contact service. Continuing to operate in emergency mode can lead to permanent failure of the compressor.
Frequently asked questions (FAQ)
Is it possible to check pressure without a pressure gauge?
It is impossible to accurately measure pressure without a pressure gauge. You can only indirectly judge the presence of gas by the sound of the stream coming out of the tube or by the temperature of the tubes, but these methods do not provide the digital values necessary for diagnosis. For a quality check, a tool is required.
What pressure should be in the refrigerator that is turned off?
In the refrigerator that is turned off and warmed to room temperature, the pressure must correspond to the saturation pressure of the refrigerant at this temperature. For R134a this is about 4-5 bar, for R600a the system may be under vacuum or have a slight excess pressure (0.1-0.2 bar).
Why does the pressure jump after refueling?
Pressure surges can be caused by air entering the system, the presence of moisture that freezes and thaws in the capillary tube, or Compressor malfunction (valve sticking). Also, the reason may be incorrect operation of the thermostat.
Is the pressure in the refrigerator dangerous for humans?
The operating pressure in household refrigerators is relatively low (usually up to 10-12 bar at discharge), which does not pose a threat of explosion as such. However, the danger is posed by the gas itself (suffocation, frostbite) and the flammability of R600a when concentrated in air. You need to work in a ventilated area.
Do you need to bleed off all the gas before checking?
No, if you just connect the pressure gauge through the Schrader valve, you don’t need to bleed off the gas. If you crash into a pipe, then the gas must be vented in a well-ventilated place away from fire sources, especially if there is R600a. It is best to use special devices for collecting freon.