Due to the evaporation and condensation of the refrigerant in a closed circuit, the thermal energy of the air is taken out and released into the environment. This is the principle of operation of any chiller. The state of aggregation and other parameters of the working substance are constantly changing. But most ordinary users are interested in only one characteristic - the pressure of freon in the air conditioner.
The background is clear: many owners of private houses and apartments want to independently maintain a split system, filling the freon in the simplest way found on the Internet. We will reveal the essence of the methodology in 3 stages - the theoretical part, diagnostics and instructions for refueling.
Why pressure does not depend on the amount of freon
Freons used in air conditioning systems and refrigerators circulate inside a closed circuit consisting of two heat exchangers (evaporator and condenser), a compressor and a butterfly valve. In the first radiator, the refrigerant passes from the liquid to the gas phase, taking away the heat of room air, and in the second it turns back into liquid. The principle of operation of the split system is described in more detail in a separate publication.
Recall: Freon is a substance boiling at a negative temperature (under ordinary conditions). To increase the evaporation / condensation point, the pressure in the circuit is forcibly increased by the compressor.
Freon pressure in the system depends on several key factors:
- ambient and indoor temperatures;
- air conditioner operating mode;
- degree of pollution of heat exchangers and air filters;
- brands of charged refrigerant;
- other, less significant factors.
Reference. Household chillers are usually charged with two brands of freons - R22 and R410a. Car air conditioners are filled with R134a freon; older models are filled with R12.
The actual pressure of the working fluid changes several times during the day due to weather and switching cooling modes. The amount of refrigerant does not have any effect, unless the substance has completely disappeared from the system. In support of these words, we describe an experiment published in the technical manual of the famous author Patrick Kotzaoglanian:
- Take 2 closed tanks that simulate the freon circuit of an air conditioning system. Connect the pressure gauges to them and fill them with a different amount of R22 refrigerant.
- We heat the vessels to the same temperature +20 ° C. All three gauges will display 8 Bar regardless of the liquid level in the tank. Why?
- When heated, freon evaporates, but the gas requires 30 times more volume than liquids. The vapor phase quickly fills the free space and becomes saturated, the pressure in the vessels increases. When the heating stops, the readings become the same.
- To verify approval, we heat 2 tanks to temperatures of 27 and 34 degrees. Pressure gauges will show growth to 10 and 12.2 bar, respectively.
Conclusion. The operating pressure in the air conditioner does not depend on the volume of freon inside the system, it makes no sense to measure it without taking into account the temperature.
How to check the balance of Freon
It is possible to determine the lack or excess of freon in the split system circuit by the amount of overheating of the gas coming from the evaporator to the compressor. Explain this concept:
- the refrigerant vaporized in the internal heat exchanger moves through the low pressure pipe to the compressor;
- on the way, the steam manages to additionally warm up by 5-8 ° C (if the amount of freon is normal);
- the difference between the boiling point of a liquid and the actual gas temperature at the compressor suction pipe is called overheating.
Key moment.To find out the boiling point of a freon of a certain brand in real conditions, it is just necessary to measure the pressure on the suction side.
For work, you will need a manometer station with connecting hoses and a contact thermometer (an electronic pyrometer is also suitable). We diagnose the remainder of freon according to the following instructions:
- Find out the type of freon used in the air conditioner by the nameplate attached to the outdoor unit.
- The blue hose leading to the low pressure gauge (abbreviated as LP), located on the left of the manifold, connect to the service port of the gas line, as shown above in the photo. It has a large diameter.
- Turn on the split system for cooling at maximum fan operation. Open the left tap on the gauge station.
- Take readings only after starting the compressor. The sound of a running unit is well heard from the external unit.
- Find out the boiling point of your brand of freon at the measured pressure, using the table.
- Using a thermometer, measure the actual heating of the gas pipe on the suction side. Calculate the difference between this temperature and the table value of the boiling point.
- Go to the analysis of the result.
Tip. Using the freon table is optional. Additional manifolds are also plotted on the manifold manometers, immediately showing the boiling point of the freon at the measured pressure. The main thing is to initially select the correct station where the markings are applied for the R22, R410a and R134a refrigerants.
Let's analyze the example shown in the photo. The arrow shows 5.4 Bar, which corresponds to the boiling point of freon R22 +8 ° C. We measure the temperature of the suction pipe and get, for example, +14 degrees, the superheat will be 14 - 8 = 6 degrees. The permissible range for all types of air conditioners, including automobile, is 5-8 ° C, which means that the amount of freon is normal.
Signs of a lack of refrigerant
If, as a result of the measurements, you get a steam overheating of more than 8 degrees, there is a lack of freon in the circuit. What happens in the air conditioner:
- The liquid boils in the first section of the evaporator and passes into a gaseous state. The steam, passing through the heat exchanger tubes and the line section to the compressor, manages to get very hot.
- Constantly absorbing hot gas, the compressor unit is poorly cooled and begins to overheat, the resource of the mechanism is reduced.
- Performance in the cold is noticeably reduced. 1 kg of refrigerant on average is able to absorb and transfer 50 watts of heat - the lower the consumption of freon in the circuit elements, the weaker the air is cooled.
Note. The problem with a lack of refrigerant arises, as a rule, due to leaks on the roller joints of copper pipelines. The main symptom is traces of oil on the nuts, knocking out along with the working fluid.
A lack of refrigerant is accompanied by other side effects:
- at the command of the sensors, the split system often turns off and shows an error;
- the compressor runs for a long time in maximum mode;
- pipes and service ports are covered with hoarfrost; in advanced cases, a snow coat increases on the edges of the evaporator.
Identical symptoms appear on car air conditioners, as they function in a similar fashion.
Oversupply and other problems
The amount of overheating was less than 5 degrees? This means that too much fluid is circulating in the system. Part of the substance does not have time to evaporate in the heat exchanger of the indoor unit, individual drops can fall into the compressor, and this is fraught with a major breakdown.
Recommendation. Refueling is relatively rare - as a rule, after maintenance of the air conditioner by illiterate personnel. If you find a problem, you should call the normal service wizard, which will merge the extra hladon or reveal another problem.
If you are confident in your own abilities, try to remove part of the freon yourself.Using the manometer on the manifold or the table, determine what pressure should be in the air conditioner during normal overheating of +7 ° C and gently bleed a small portion of the gas.
Abnormally high or weak overheating occurs not only due to the refrigerant, but also various malfunctions:
- throttle valve capillary tube clogged;
- malfunctioning compressor or dryer;
- the four-way solenoid valve is defective, reversing the cycle to the other side (cooling / heating modes).
These problems are solved in one way - by calling the wizard, an ignorant user simply will not be able to diagnose them. If manipulation with the freon did not produce a result, call the service department.
Refueling by pressure and superheat temperature
We want to warn you right away that this method of adding freon is considered unreliable, although many refrigerators fill freon “by eye”, focusing only on pressure. The best and most correct charge method is to completely replace the refrigerant with emptying the system and filling by weight, as described in our manual.
In addition to the thermometer and gauge manifold, you will need:
- hex and open-end wrenches;
- electronic scales (suitable for kitchen);
- Freon of the required brand (indicated on the plate of the outdoor unit).
An important point. Different types of refrigerants have different physical properties. The concept of interchangeability or compatibility of these fluids is absent as such, only the gas indicated on the plate of the refrigeration unit is suitable. In household air conditioners, brands R22 and R410a are used, in cars - the 134th freon.
First of all, make sure there are no leaks, otherwise you risk wasting time and effort in vain. When refueling, follow the instructions:
- Connect the hose from the LP gauge to the service port, and the middle yellow tube to the gas bottle in accordance with the diagram below.
- Open the cylinder valve and blow out the hoses from the air by opening the high pressure valve for a second (on the right of the manifold).
- Put the container with hladon on the scales, zero the readings. When pouring Freon R410a, the cylinder is placed upside down.
- Turn on the air conditioner for cooling and open the service valve by first unscrewing the protective cover.
- Opening the LP valve (on the left of the gauge station), start the freon into the circuit in small portions, literally 30 grams. Be guided by electronic scales.
- After pouring each portion, turn off the tap and measure the temperature of the gas pipe for 1-2 minutes. Serve the next batch if necessary. The task is to reduce overheating to normal 5-8 ° C.
- At the end of refueling, close the manifold, service pipe, and cylinder valves one at a time.
Example. If earlier the temperature of the gas line at a pressure of 5.4 Bar was +17 ° С, the superheat reached 17 - 8 = 9 degrees (Freon R22). So, it is necessary to achieve cooling of the tube to + 14 ° C in order to meet the norm.
The technology for refueling a split system for overheating and pressure is described in detail in the video:
Conclusion
Usually the question of the required pressure of freon inside the air conditioner makes classroom refrigeration technicians nervous. You need to understand that a definite answer does not exist in nature, since this parameter depends on many factors and often changes. You should always consider a combination of two characteristics - pressure - temperature, otherwise interference with the "split" can lead to serious damage.