How to charge or add

Freon or Refrigerant to your

Air conditioner or Heat pump.

The following material is somewhat controversial. There are many who would like to make sure that the average homeowner will never work on their own equipment and the industry has gone to great lengths to get the government to regulate the use of refrigerants by the average person. In short blame the last person that you voted for who got elected to office. If you want to learn more about law here is a good fun place to start.
I will not discuss the legality of handling refrigerants please take that up with the appropriate authorities. I will simply be telling you how to know if your system needs refrigerant and how to know how much to put in. But surf-ice it to say that there is a correct amount of refrigerant that should be in your system and adding any more will not make it work any better but will cause damage.
On a recent showing of "Dateline NBC" they set up 8 companies in the Houston Texas area. After checking out this Trane system thoroughly they let each company look at it and every one either added 2 pounds of R22 or said it needed 2 pounds. by the time they were done this system had over 4 pounds (that is what they reported) of excess refrigerant in addition to what was already in there. I can understand the first charge but after that the head pressure on that system must have been over 300 psi and by the end of the show the system must have been over 400 (the compressor should have gone off on internal relief). I am guessing that is why they chose to use a Trane or American Standard system. That just goes to show how crooked this trade has become.

Just about every one is familiar with a gauge manifold, it is those two gauges that have hoses coming out that everyone who has ever done any refrigeration work has. There are two gauges on that manifold one for low pressure (also known as suction) one for high pressure (also known as head). By using these gauges you can tell a lot about how your system is working but the gauges will not tell all you need to interpret them as well as monitor other things like the temperature of the refrigerant lines.
The Suction pressure is a reflection of how well the evaporator portion is picking up heat (higher) and how well the compressor is removing it (lower). The Head pressure is a reflection of how well the condensing coil is getting rid of the heat (lower) and how much load the system is putting on it (higher). It may sound like a contradiction but high or low pressure is a good thing depending on what is causing it. In general you want the suction pressure to be as high as possible without it being caused by an over charged condition and the head pressure to be as low as possible and still maintain a full liquid line. High efficiency units will have higher suction pressure and lower head pressure than an older unit depending on the size of the coil and the airflow.
Simply put what makes one unit more efficient than another is bigger coils in relation to the compressor capacity. This is the dirty little secret that no one wants to talk about.
Want a really efficient system add a second compressor that is half the system rating (picture added soon), Trane has one that is a 4 ton system with 2 2ton compressors or a Lennox Two Speed if you can find one.
Enough of my rant now back to the subject at hand.

From all my experience I can tell you that an airconditioning system is correctly charged when the liquid line leaving the condenser is full of liquid refrigerant. Adding more refrigerant will simply waste space in the condenser and reduce efficiency and raise the head pressure. The other issue is how well the refrigerant is being fed into the indoor coil. Most older residential systems use capillary tubes, newer equipment uses a drilled piece of metal called an accurator, piston or orifice, real systems use a thermostatic expansion valve (TEV) to regulate refrigerant flow. As far as I am concerned your system is not working correctly unless it has a thermostatic expansion valve. The difference is that mechanical restriction works only for certain conditions but a TEV. will deliver the right amount of refrigerant no matter what the head pressure is and allow a perfect charge (full liquid line without a drop more). Without this device you will have situations where you have to add excess refrigerant to raise the head pressure to push the refrigerant through the coil or the restriction lets too much refrigerant through and you have a liquid line that has hot gas mixed in with it and does what is called "flooding" or "slugging" the compressor (a bad situation). In either case the system is not working correctly and there is no "right" amount of charge that will make it work right. If you have restricted capillaries like we have seen on too many Rheem/Ruud units the coil will turn to a block of ice (cooling mode) and the compressor will run very hot no matter how much refrigerant you add to run up the head pressure. The solution to this is to replace the indoor coil with one that has a TEV. and a larger capacity and watch the system work better than ever.

Rheem/Ruud indoor coil with thermostatic expansion valve.

Image of Rheem/Ruud heat pump indoor coil with thermostatic expansion valve. A system that doesn't have one of these inside (cooling) and out (heating) cannot be the best that it can possibly be.
Changing the indoor coil to one like this can bring new life to an older malfunctioning system and it can work better than a new one that doesn't have this feature.

The suction pressures shown are for cooling mode. Heating mode will be lower. Head or high pressures will be simular from heating to cooling. One of the methods of charging that I have read about that seems to make sense when explained properly is to add charge as long as the suction line keeps getting colder as soon as it starts to show low super heat (I will explain that later) then there is too much refrigerant; you don't want to flood the compressor or run the head pressure to high. What I usually do on a system that is not a TEV. is to charge until the suction pressure gets above 55-60 psi then add more until the suction line starts to get cold. remember more efficient systems will have higher suction pressures (80 psi is not uncommon). I also watch my head pressure to make sure there isn't other problems (175-200 is good anything above 250 is cause for concern). If the pressure is above 300 then there is definitely something wrong like a very dirty coil or the system is simply overcharged. The compressor (hermetics {piston} not scrolls or rotary) will have a ball of sweat around where the suction line enters, what Mr. Forest Grauel calls a "happy compressor". If the compressor becomes a ball of sweat then the system is feeding too much refrigerant into the indoor coil. If it is dry then there is a restriction (suction pressure will usually be low; below 50 psi cooling mode and ice will start to grow).

Image of Sporlan liquid line sight glass

Image of a sporlan sight glass connected to a filter dryer after a liquid line solenoid valve. When the sight glass is clear like this the system is fully charged. Adding any additional refrigerant will just back up into the condensing coil (outdoor in cooling mode, indoor in heating mode) If the suction pressure is still low and the refrigerant is not feeding properly then you have a problem with the metering devices. Adding this device is the easiest way to diagnose a problem system.
See also the page on icing.

I Work very long days and sometimes I end up working on this stuff at 3 or 4 am after having been up since 10 am. So some of the information is incomplete and there are some errors here which I will try to correct when I get a moment to sit down and go through this. So I will continue this page when I have more time but for now please follow the links below. If there are any volunteers out there who would like to help me write this please knock your self out. In a nut shell don't over charge your system.

This page will be continued later:
Scott Meenen can be reached at 240-460-3820

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Written By: Scott Meenen N3SJH of
G&S MECHANICAL SERVICES.
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How to charge or add

Freon or Refrigerant to your

Air conditioner or Heat pump.

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