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Gas charge, how to do it correctly

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Gas charge, when is it necessary?

A gas charge or a gas refill in our air conditioner should not be never necessary, unless we had a gas a leak in our refrigerating circuit. These gas leaks can be produced due to many reasons that we already talked about in another previous article and before any charge the leaking should be found and fixed, and in order to do that we should identify first that our air conditioning breakdown comes determined because of a refrigerating leak and once this problem is cleared, we should look for and solve this leak before doing any gas charge.

If you have any doubts about if your air conditioner lacks of gas  or if what you need is to find this leaking, these two articles will help you to determine whether it exists or not a gas leaking and if so, try to find where the gas leaking is.

How to find out if an A/C lacks of gas

Most common gas leakings and how to find them

Necessary tools in order to do a gas charge

If we already know that our machine is without gas, we have looked for the leaking and we have fixed it, now it’s the time to do a gas charge to bring our air conditioner back to life. In order to do that, and most of all, to do it correctly, we will need some typical tools any refrigerator repairman has:

  • Vacuum pump
  • Manometer
  • Scale
  • Bottle of refrigerating gas that our air conditioner uses.
Vacuum pumpmore
Bottle of fluorated gasmore
A/C scalemore

Steps we have to follow in order to do a correct gas charge:

Connect manometers

Find the inlet or inlets and connect any hose in its place.

The very first thing we have to do is to connect manometers’ hoses to the valve core of our air conditioner. There are some machines that have two valve core inlets (high and low pressure), however, there are other machines that only have a single inlet. These last ones tend to be split units and the most common ones in any house. This valve core inlet will be high pressure when we have the machine running in heat pump mode and low pressure when the machine runs in cold mode.

If your equipment has two valve core inlets, we will connect the red hose in the high pressure inlet and the blue hose in the low pressure inlet.

If your equipment only has one valve core inlet, depending on the time of the year we will have to connect one or another. The blue one if we are going to turn on the machine in cold mode and the red one if we think we will turn it on in heat pump mode, because this valve core, as we said before, will become high or low pressure depending on if we select one working mode or the other one.

Do the vacuum

Once the manometer is connected to the valve core inlet or inlets, we will connect the yellow hose (the one which is in the middle) to the vacuum pump inlet, because it is advisable and necessary to do a good vacuum to the refrigerating circuit before doing any gas charge.

Doing a vacuum to the machine refrigerating circuit is necessary for many reasons:

  1. It eliminates the air the refrigerating circuit has.
  2. It eliminates the moisture which could be inside the refrigerating circuit.
  3. It helps to do the gas charge, because it will help the refrigerating gas to come inside faster when there is no air inside the circuit.

Once this is done, we will turn on the vacuum pump and we will let it work for a while. But, how much time is “for a while”? Well, it depends. It depends on  the kind of installation, how big the machine is and the distance between pipes. It also depends on the vacuum pipe capacity and it also depends on the kind of leaking we have and how much time the machine was without gas. Nevertheless, if we have any doubts it’s better to let the machine work during a longer period of time than a shorter one.

In general, if a machine hasn’t lost entirely its gas, it isn’t possible neither air nor moisture to enter into the circuit, because any tiny amount of gas remaining in the refrigerating circuit will be enough to keep the pressure of this higher tna the ambient pressure and therefore to avoid the air entrance.

Gas charge

Once the vacuum is completed, it’s time to charge the gas. Nowadays there exist and are used many kinds of refrigerating gas (R-22, R-407, R-410, R-424, ISCEON, etc.). Some of them are azeotropic and some of the aren’t. We are going to do the gas charge in a valid way for any kind of gas. This way will be in liquid state and by weight.

Why the gas charge must be done with the refrigerating gas in liquid state

Gas charge scheme

In order to do this refrigerating gas charge we are going to need a scale and the refrigerating gas bottle itself, for the best way to do it is, as we said before, by weight and with the refrigerant in liquid state.

Before putting the bottle on the scale, there are a few things we have to consider with the gas bottle.

Putting the bottle on the scale properly

There are many kinds of bottles depending on manufacturers, some of them (bottles) have two independent inlets for gas and liquid, others only have ine inlet with or without a case. This is important to know because for this it will depend if we have to turn the bottle or not.

The very first thing we have to do is to put the refrigerating gas bottle on the scale and plug the yellow inlet that we had plugged in the vacuum pump in its inlet. Once we have done that, we should turn on the scale in order to set it in 0,000 kg., for we are going to measure charge and gas quantity which enters as the bottle loses weight.

Having this all set, we have to open the bottle and then open the manometer valve to let the gas go through and start entering the refrigerant in our air conditioner. The gas charge time will depend on many factors, such as: the bottle pressure, how much refrigerant is left, the temperature, etc. But between five and ten minutes should be enough, unless the pressure of both (bottle and machine) got balanced and gas coulnd’t enter. In that case, it will be necessary to turn the machine on for the pressure to lower and to sucks in gas.

Remember that the gas charge with our air conditioner working will only be possible low pressure via, so if we have an air conditioner which has two valve cores (high and low) we will open only the one with low pressure in order to keep on the refrigerating gas charge, and if our unit only has one valve core inlet we must tur the unit on in cold or dry mode, because in heat pump mode the pressure would be too high and we would be doing the opposite (entering gas from the machine to the bottle).

Once we see that our scale has substracted the same quantity of gas that our equipment needs, we will close the bottle and also manometers and we will consider the work is done.

The best way to charge an A/C is doing it by weight and in liquid state

How much it costs an A/C gas charge:

A very common doubt is what’s the price of a gas charge and it’s pretty logical because it doesn’t depend on neither just one factor nor it’s something standardised. Factors to mesure gas charge price are many and we explain you here briefly:

  • Kind of fluorated gas: There exist many kinds of fluorated gas or refrigerating gas which are used in A/C units. The most common ones are the R410, R407, R22 and their replacements like RS44 / R424A (there are too many others).
  • Fluorated gas taxes: Depending on the country you are living in, it can impose a tax on this kind of gas, talking about Spain, these taxes depend on how much these kind of gas contribute to globar warming. Some gas pay more taxes than others.
  • Gas quantity: It isn’t only important the kind of gas and its special tax, we also have to be aware of the amount of gas our machine uses. In general, split A/C units which are around 2k or 3k frigories use to need a kilo of gas. However, pipe units or central household air conditioner units use to need between three and five kilos.
  • Installer company or technician margin: This is the only variable point of the equation because the amount of gas we need will be indicated by our machine in its technical characteristics. The tax is something which comes with law and therefore it’s a stable value. But the margin given by a technician doing his/her job, handling or costs will be in the end what determines exactly our gas charge price.

How to know quantity and kind of gas your air conditioner uses

As you can see, in order to do a precise estimate about how much can a gas charge cost, we need some facts that we can easily find out by looking the technical characteristics in our machine and, of course, by asking to the repairing company how much it costs or how much we will have to pay for every kilo of gas. The price a technician uses to levy it may vary between 20 and 60€ per kg. + taxes + VAT.

 Calculate approximate price of a gas charge

David Macías :