Operation absorption refrigeration units, such as the popular models Gazelle or Nord, often require the intervention of qualified personnel when there is a loss of refrigerant. Unlike compressor analogues, a water-ammonia mixture circulates here, which is under high pressure and is toxic. The process of restoring the functionality of the unit is not just “topping up”, but a complex technological operation that requires strict adherence to safety standards.
Before starting work, you must clearly understand that self-refueling without special equipment and skills can lead to irreversible consequences. Ammonia is not an inert gas, but an active chemical compound, which in certain concentrations forms explosive mixtures with air. In addition, an incorrect proportion of the components of the mixture can permanently disable the diffusion pump, which is the heart of the absorption system.
In this article we will analyze in detail the technical nuances of the procedure, the necessary equipment and the algorithm of actions for specialists. It is important to understand that we are talking about professional service, and not about home repairs “on the knee”. Any deviation from the technology is fraught with depressurization of the circuit or mechanical destruction of the unit components.
⚠️ Attention: Ammonia belongs to the 4th hazard class. If leaked, it causes severe irritation of the mucous membranes and respiratory tract. Work may only be carried out in well-ventilated rooms or outdoors using personal respiratory protection.
Operating principle and composition of the refrigerant
Absorption refrigerators operate on the basis of a thermodynamic cycle, where the circulation of the refrigerant occurs due to heating rather than mechanical compression. The working fluid here is a binary mixture consisting of ammonia (refrigerant) and water (absorbent), often with the addition of an inert gas such as hydrogen or helium. It is this combination that allows you to create low temperatures in the evaporator without the use of moving parts in the cooling circuit.
During operation, ammonia evaporates at low pressure, taking heat from the chamber, and is then absorbed by water in the absorber. Heating this mixture in the generator again releases ammonia, which condenses and returns to the cycle. Violation of the concentration of components leads to the fact that diffusion pump the solution ceases to effectively rise, and cold ceases to be produced.
Often users confuse conventional compressor refrigerators with absorption ones. If your device has a compressor (you can hear the hum of the motor), then it uses freons (R134a, R600a), and refilling them with ammonia is strictly prohibited. Ammonia systems are usually silent (only gurgling can be heard) and are often found in Soviet models or motorhomes.
It is critically important to determine the exact model of the unit before starting work. The specifications indicated on the nameplate dictate the required pressure and type of fill gas. Using the wrong refrigerant can lead to a chemical reaction inside the system, pipe corrosion, or even an explosion.
Required equipment and safety measures
To carry out high-quality refilling, the technician will need a specialized set of tools, which differs significantly from the standard set for freon. The main element is a vacuum pump capable of creating a deep vacuum, since the system must be absolutely dry. The presence of moisture in the absorption refrigerator circuit is unacceptable and will lead to freezing of water in the throttle tube.
There is also a pressure gauge station with hoses that are resistant to the aggressive environment of ammonia. Conventional rubber hoses can quickly deteriorate when exposed to ammonia, so special hoses with an inner layer of synthetic materials are used. The dosage of the mixture must be accurate to the nearest gram, which requires high-precision scales.
- 🛡️ Protective suit and a gas mask with an ammonia filter is a mandatory requirement for a specialist.
- 🔧 Gauge collector with a vacuum gauge to monitor the pressure in the circuit.
- 💨 Vacuum pump with a capacity of at least 4 cubic meters/hour for high-quality air evacuation.
- ⚖️ Electronic scales with 1 gram increments for accurate weighing of the refilled substance.
In addition to tools, it is necessary to prepare a container with water to check the tightness of connections and neutralize possible micro-leaks of ammonia. Water perfectly absorbs ammonia, forming ammonia, which reduces the concentration of vapors in the air. The workplace must be equipped with forced exhaust ventilation.
⚠️ Attention: It is strictly prohibited to use open sources of fire or sparking tools near the work site. Ammonia mixed with air is explosive at a concentration of 15 to 28%.
Diagnostics and preparation of the system
The first stage of work is a thorough diagnosis of the system for leaks. Even if the refrigerator simply stops freezing, this does not always mean there is a lack of refrigerant. Often the cause is a clogged capillary tube or failure of the heater. Therefore, before refueling, it is necessary to ensure the integrity of the circuit.
Checking is carried out using the nitrogen pressure test method. The system is filled with dry nitrogen under pressure exceeding the operating pressure (usually up to 15-20 atmospheres) and left for a day. If the pressure gauge shows a drop in pressure, it means there is a fistula somewhere. In absorption refrigerators, this often occurs in the area of the generator or evaporator welds.
How to find a microcrack?
If visual inspection and a soap solution do not help, use a helium leak detector. It allows you to detect leaks in places inaccessible to the eye, for example, inside thermal insulation or in complex diffuser assemblies.
If the tightness is confirmed, the vacuum process begins. This is the longest and most important stage. It is necessary to remove not only air, but also moisture vapor from the system. Evacuation is carried out in several stages with “warming up” of the system (light heating of the generator) to evaporate moisture from hard-to-reach places.
Evacuation time depends on the volume of the system and the power of the pump, but is usually at least 2-3 hours. The residual pressure should reach values close to technical vacuum. Only after this you can start refueling. Neglecting this stage will lead to the formation of ice jams and failure of the unit.
Refilling technology and dosage of components
The refueling process itself requires precise adherence to proportions. Absorption refrigerators are not filled with pure ammonia, but with a ready-made ammonia-water mixture of a certain concentration, or the components are pumped sequentially in a strict order. The dosage depends on the specific model and is indicated by the manufacturer in the technical documentation.
Refilling is done through the process pipe, which is usually located on the rear wall of the unit. A cylinder with ammonia or a mixture is placed on a scale, and the refrigerant is supplied to the system in the liquid phase (the cylinder is turned over) or in the gaseous phase, depending on the requirements of the instructions. The pressure in the system is controlled by a pressure gauge.
| Parameter | Value / Description | Units of measurement |
|---|---|---|
| Working pressure (R717) | Depends on the condensation temperature | Bar (atm) |
| Charging mass | Strictly according to the passport (usually 50-150 g) | Gram |
| Ammonia concentration | Optimal 30-35% in water | Percent (%) |
| Addition of inert gas | Hydrogen or Helium | Atmospheres |
After filling the main circuit ammonia mixture, it is often necessary to inject an inert gas (hydrogen) to create the required partial pressure in the evaporator. This allows the ammonia to boil at lower temperatures. The pressure of the inert gas is also strictly regulated.
☑️ Refilling checklist
It is important not to over-pump the system. Excess ammonia will lead to the fact that it will not have time to evaporate completely and will enter the absorber in liquid form, which will disrupt circulation. Lack of refrigerant will not allow the desired temperature to be reached. Accuracy is a key success factor.
Launch and performance check
After filling is completed, the process pipe is sealed and a test run of the unit is performed. At this stage, the master must carefully monitor the behavior of the system. In the first minutes of operation, uneven heating of the generator or noise may be observed, which is normal for the ramp-up stage.
Checking is carried out based on the evaporator temperature. After 15-20 minutes of operation, the lower part of the evaporator should begin to cool. If you use a thermal imager, you can visually track the temperature distribution. Uniform cooling of the entire area of the evaporator indicates proper circulation of the mixture.
The absence of extraneous sounds other than quiet gurgling is also checked. A loud hissing or whistling noise may indicate a clog or improper pressure. If within an hour the temperature in the chamber does not begin to decrease, there may be air left in the system or the proportion of the mixture is incorrect.
The final step is to check the tightness of the sealed areas using indicator paper or a soap solution. Even a microscopic leak will lead to loss of performance over time. After confirming stable operation, the refrigerator can be put into operation.
Typical errors and their consequences
One of the most common mistakes is refueling “by eye” or by analogy with other models. Each model of absorption refrigerator has a unique system volume and hydraulic resistance. A violation of the ratio of water and ammonia by even 5-10% can completely stop circulation in the diffusion circuit.
Another common mistake is insufficient vacuuming. The remaining moisture freezes in a narrow section of the capillary tube or throttle, blocking the passage of the refrigerant. Visually this looks like a lack of cold, although the compressor (heater) is working properly. Removing such a blockage requires repeated evacuation and heating.
- ❌ The use of low-quality ammonia with oil impurities leads to contamination of the porous structure of the absorber.
- ❌ An attempt to refuel under pressure without evacuation forces air inside the system, creating an air lock.
- ❌ Overheating of the generator during refueling can lead to the decomposition of ammonia and an increase in pressure to critical values.
It is also dangerous to ignore the condition of the thermal insulation. If the insulation is damaged during the filling process or has become unusable over time, the refrigerator’s operating efficiency will be low, regardless of the quality of the filling. Heat gains will negate the operation of the system.
⚠️ Attention: Specifications and refrigerant requirements may vary depending on the model year and regional environmental standards. Always check the manufacturer's current technical documentation before starting work.
Frequently asked questions (FAQ)
Is it possible to fill an absorption refrigerator with ordinary household ammonia from a pharmacy?
No, absolutely not. Pharmaceutical ammonia is an aqueous solution of low concentration ammonia with many impurities and fragrances. The refrigerator requires highly purified anhydrous ammonia or a special mixture of precisely adjusted concentrations. Impurities will cause corrosion and clogging.
Why does the refrigerator work after refueling, but does not freeze?
Most likely, the proportion of the mixture is incorrect or there is air (nitrogen) left in the system, which creates a gas lock. Also, the cause may be insufficient vacuuming, due to which moisture has frozen in the capillary. Repeated evacuation and refueling are required.
What is the danger of getting ammonia on the skin?
Liquid ammonia causes severe chemical burns, similar to thermal ones. If contact occurs, immediately rinse the affected area with plenty of water and consult a doctor. Ammonia vapors are also dangerous to the eyes and lungs.
How long does a refrigerator last on one refill?
If the system is working properly and there is no mechanical damage (vibration, shock), refilling is not required during its entire service life - 10-15 years or more. Loss of refrigerant indicates depressurization of the circuit, which must be eliminated before refilling.