How to make vacuum in the air conditioning

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The importance of vacuuming in air conditioning

Many of the technicians do not know how harmful it can be for the system and the quality of the service if the vacuum in the air conditioning is not done correctly, this is in many occasions because they do not know the potential failures that can be produced in the equipment after its starting, causing to have to return in several occasions by failures in the same one, failures that can get to be very serious and expensive as a change of compressor.

What happens if you don’t vacuum the air conditioner?

The first thing that happens is that there is the presence of non-condensable gases in the circuit -air- that can cause the following problems that are not visible but that seriously affect the functioning of the equipment.

• That the temperature in the high-pressure part of the refrigeration system rises.
• That the compressor discharge valve gets hotter than it should.
• That organic solids form in the compressor that can end up damaging it.

Another problem associated with not making a vacuum in the air conditioning and its installation is the presence of humidity in the system, something very recurrent especially in badly made pre-installations and that can cause the following problems:

• The presence of moisture in the system can cause problems in the compressor, because the drops of moisture are not compressible by the compressor, which can create deformation and breakage in the most fragile parts of it, such as connecting rods or pistons.
• Ice inside the refrigerating circuit, the small drops of water that can remain inside the refrigerating circuit for not making a vacuum, together with the low temperature of the refrigerating gas that circulates inside, can produce that these drops end up freezing creating pieces of ice and blocking some essential parts of our air conditioning like the expansion valves and capillaries.

But what if the two problems come together on our circuit?

When air and moisture trapped inside a refrigeration circuit are combined with a chlorine- or fluorine-based refrigerant gas, the perfect conditions are created for the generation of a chemical hydrolysis effect.

From this mixture and depending on the type of gas used in the installation, hydrochloric and/or hydrofluoric acids are obtained, as well as sludge in the system that is lethal for hermetic and semi-hermetic compressors, since it causes premature anomalies in the electric motors contained in its interior, attacking the insulating varnish of the same, to the point of damaging the compressor by diversion to earth.

So how do you vacuum the air conditioner properly?

The first and most obvious thing to take into consideration is that a good vacuum has to be done with a vacuum pump and NEVER with the machine’s own compressor, since this would cause problems to it and we would be making the situation even worse.

In order to carry out a correct vacuum to the air conditioning installation, it is essential to have a vacuum pump suitable for the type of installation and the cooling power of the system in which we want to carry out the operation, since in a domestic installation it is not possible to use an industrial vacuum pump or vice versa, since we would either go too far or we would not reach the optimum vacuum conditions required.

Another very important tool when measuring the quality of the vacuum and its realization, will be the use of a vacuum gauge, since it will measure much more effectively than a manometer if the vacuum has been done correctly -manometers generally cannot measure the microns of vacuum-, at present and with the presence especially of polyolester oil -POE-, the use of the vacuum gauge has taken great importance to achieve the correct level of vacuum.

With these two tools and the nitrogen we will perform the procedure called ‘triple evacuation’

Steps to follow to make a correct vacuum to the refrigerating circuit with the triple evacuation

Although this is the best method to carry out a vacuum correctly, it will not always be necessary to do it this way, since if the installation is very simple – installation of split air conditioning or domestic ducts -, we have stored the installation materials – copper pipe – in a clean, dry place with the ends closed and we finish at that moment to carry out the whole installation, we do not run the risk that in our installation there could be traces of humidity, so a simple vacuum would be enough.

On the contrary, if the installation has symptoms of moisture, has been left outdoors or has been installed under an existing pre-installation and we see that this is not in perfect condition, if it is advisable to perform the entire process.

This triple evacuation consists of 3 stages:

1st Stage

• Connect the vacuum pump to the refrigeration circuit in both lines – high and low pressure.
• Start the vacuum pump.
• Stop the vacuum when you get a reading of 800 millibars of vacuum.
• Break the vacuum with nitrogen, pressurize the system to buzzer pressure and wait 30 to 60 minutes.
• Finally, release the nitrogen.

2nd Stage

• Start the vacuum pump.
• Stop the vacuum pump when we get a reading of 800 millibars of vacuum pressure.
• Break the vacuum with nitrogen and pressurize the system for 30 to 60 minutes.
• Release the nitrogen.

3rd Stage

• Start the vacuum pump.
• Stop when you have a reading of 250 or 500 millibars depending on the type of lubricant* used by the installation.
• Break the vacuum with the refrigerant gas – if the outdoor unit has gas, open the service key, if the gas needs to be added, forget this step and move on to the next one.
• Gas charge in liquid state the circuit-add gas if the unit already had the refrigerant inside and if necessary or gas charge completely if the outside unit is out of gas-.

*500 millibars if working with mineral oil or polyolester oil (POE)

*250 millibars if working with polyalkylene glycols (PAG)

The importance of liquid gas charging with today’s refrigerants

What happens when you vacuum the air conditioning system

When we connect and turn on the vacuum pump to the installation, we are eliminating all the air that could have the refrigerating circuit, that is obvious, what is usually not known is that this vacuum apart from lowering the pressure inside the circuit, modifies the boiling point of water -humidity- causing it to boil and evaporate at room temperature, this evaporation of moisture makes the vacuum pump can absorb these vapors and expel them to the outside for disposal, getting therefore dry inside the circuit.