Freon Electronic Leak Detection
The easier and quickest method of leak detection is the electronic sniffer—that will usually lead the technician to the general area. Sometimes I wrap the suspected part in plastic to capture the fumes, so the sniffer can be more specific

Bubble leak method
If  the leak is big enough, we introduce high pressure nitrogen ( an inert gas) and use soap bubbles to pinpoint the leak. Sometimes you can actually feel a breeze or hear it hissing out from the leaking Freon.

The UV light/Spectronic Method
The most precise method  for locating Freon leaks is for the technician to install a liquid tracer into the system, and allow it to circulate about two weeks. A small amount of fluorescent dye is added to an air conditioning, refrigeration or industrial fluid system and allowed to circulate. The dye escapes with the system’s refrigerant or fluid and remains at all leak sites. When the system is scanned with a Spectroline® TITAN® UV/Blue™, Blue Max Plus™, or ultraviolet inspection lamp, the dye fluoresces brilliantly to pinpoint the exact source of every leak. Proven to find multiple and intermittent leaks undetectable by any other method. Even leaks smaller than 1/8 ounce per year!
Easily verify repairs by removing the dye from the leak sites with GLO-AWAY™ dye cleaner and then re-inspect. The dye can remain safely in AC&R or fluid systems indefinitely for future leak inspections.
Fluorescent leak detection is the only method that can be used for both accurate diagnostics and as part of a comprehensive preventive maintenance program.
AR-GLO® fluorescent dyes are the only dyes that are co-solvent free and OEM-approved by major compressor, refrigerant, lubricant and AC&R equipment manufacturers.
AR-GLO dyes are super-concentrated, lubricant-specific and proven in over 40 million AC&R systems worldwide.
AR-GLO dyes are completely safe and will not alter or impair lubricant properties, which could lead to equipment damage and costly downtime. They have been successfully tested in accordance with ASHRAE Standards 97 and 86.

There comes a day when the air conditioner stops cooling and you call your local HVAC contractor for HVAC service and repair. The HVAC service technician arrives and checks the filter and some other things. You see him go to his truck and get some tools and a set of gages while you hope for the best. Ten minutes later he comes back to report to you that your air conditioning unit is low on refrigerant. Now comes the time when you need to understand why the air conditioner needs refrigerant and what to do next?

First of all the air conditioner or heat pump (if you have a heat pump) does not consume Freon or refrigerant. The system is a sealed system and the air conditioner does not burn or use up refrigerant to make your house cool and/or warm if you have a heat pump. The refrigerant or Freon (Freon is a registered trademark name of Dupont Corporation and is widely used to described the refrigerant in you air conditioner or vehicle air conditioner) in your air conditioner or heat pump is supposed to be locked in a hermetic system and sealed tight. From time to time a leak occurs in the air conditioning system and the unit needs to be charged so that it can continue doing its job of cooling the home or business. As the refrigerant leaks out of the system still cools. It actually cools too much. The indoor evaporator coil begins to freeze up because the temperature of the coil drops below the dew point. This is humidity or moisture in your home or business which passes through the air conditioning (or heat pump) indoor coil for conditioning. The air conditioning system experiences a reduced amount of air flow because of the coil icing up. You may notice ice on the lines which run to the outside condenser. If you see this it is important to shut the system off immediately and call your HVAC service company. If the system is left running the indoor evaporator coil could turn into a block of ice and no air flow will come out of the vents. Freon leaks can be extremely frustrating. They can  lead to freeze-ups which can lead to compressor damage (the heart of the system). Location and repair of refrigerant leaks is a challenging assignment—not for amateurs. Repairing a Freon leak can be as simple as tightening a valve core or tightening a schreader cap seal.. It can be as expensive as replacing an evaporator coil, condenser coil, or copper line set.
If your system is low on Freon, it's because it leaked out. IT DOES NOT DISSIPATE OR BREAKDOWN!. So where did it go? Here are some possible solutions to where the problem may lie…valve cores, weld joints, electrical connection to the compressor body, or the copper tubing itself .

Here are the reasons why your Air conditioner has a Freon or refrigerant leak: 

1)  A schrader valve is leaking Freon and needs to be replaced. There is a tool which can be used to change this schrader valve without having to recover the entire amount of refrigerant from the system. These schrader valves look like the little valves in your tire on your car and they hold the refrigerant in the system and allow the technician to access the system to test the pressures. These schrader valves are necessary and sometimes the rubber seals deteriorate or the schrader valve gets stuck and allows Freon or refrigerant to leak out of the air conditioner system. Consider yourself lucky if this is the problem because it is easily repaired.

2) If you have a heat pump heat pumps have accumulators. Accumulators are necessary for the heat pump system to provide heat in the winter and protect the compressor from liquid slugging. Accumulators are usually made from steel and after a few years they begin to rust. These rust holes allow Freon or refrigerant to leak out of the heat pump system. The heat pump accumulator can be replaced but the entire system needs to be recovered and a new accumulator installed. The new accumulators sold on the market today are also made of steel and will eventually leak after rusting occurs in the future. It is hard to say what the average life expectancy of an accumulator is and depends on quality of steel used to make the accumulator so the time varies on when the accumulator will leak. To prevent this from occurring in the future with a new accumulator or new heat pump it is not a bad idea to spray the accumulator with some sort of rust preventing paint. 

3) A capillary tube is leaking on the inside evaporator coil or if you have a heat pump on the outside heat pump condensing unit. These capillary tubes are very small copper tubes and over time and through vibration of the system they rub together or rub against another piece of metal and a hole appears on the capillary tube and Freon or refrigerant leaks from the air conditioning or heat pump system. These leaks can be difficult to find because disassembly of the system is necessary in order to find the leaking capillary tube. When the leak is found the capillary tube can be cut, the hole for the capillary tube reamed, and another larger piece of copper tubing soldered over the capillary tube. This does not apply to capillary tubes which connect metering devices to thermostatic expansion valve (TXV) bulbs. These TXVs need to be replaced and do not contribute to leaking Freon from the system.

4) If the air conditioning or heat pump system has any flare connections leaks generally occur at these connection. Sometimes these flare connections can easily be repaired while other times the flare fitting and connection has to be replaced and remade completely to prevent future leaks.

5) The indoor or outdoor air conditioning or heat pump coil is leaking and needs repair or replacement. Most of the time the leaks in the coils (whether they be outside or inside coils for an air conditioning or heat pump system) occur at the u-tubes or bends in copper at the end of the coil. There is a tube sheet made of sheet metal which holds the coils together and over time and through vibration the u-tube part of the coil rubs against the tube sheet and a refrigerant leak occurs.  Sometimes this can be easily repaired but other times it the coil needs to be replaced. Depending on the age of the unit indoor and outdoor coils are available for replacement. The problem with leaks near the tube sheet is when the technician uses heat to repair the leak in the coil the heat loosens other parts of the coils and another leak could occur. It will take a very good technician who knows how to braze very well in order to repair this type of refrigerant leak.

6) Filter dryers are installed in all refrigeration systems and are necessary for absorbing minute amounts of moisture in the system and for filtering trash before it gets to key components which could be damaged or plugged if the trash were allowed to get to the components. These filter dryers have screens and desiccant inside them and the outer shell is made if steel. The same problem that occurs with a heat pump accumulator will eventually occur with a filter dryer and a refrigerant leak occurs. These filter dryers are easily replaced but only after recovering the entire amount of refrigerant or pumping the entire amount of refrigerant contained in the air conditioner or heat pump system into the condenser.

7) The line set which carries refrigerant back forth from the condenser to the evaporator coil has been pierced or damaged. Damage can occur from a lawn mower or someone tripping over the line set. Additionally, line sets generally run in voids inside walls and ceilings just below the roof. I once had a line set which was pierced by a nail when the roof was replaced. The refrigerant took a year to leak out before the air conditioner was no longer functional and the customer required an HVAC professional to troubleshoot and repair the air conditioner system.

Refrigerant Leaks Final Advice

That covers the major types of refrigerant leaks which occur with air conditioner and heat pump systems. Depending on the age of the air conditioner or heat pump system and the type of refrigerant leak which occurs may determine whether or not you decide to replace the air conditioner or heat pump system. Many air conditioning and heating service and repair companies will not provide a warranty for refrigerant leak repairs simply because it is possible to repair one refrigerant leak and have another refrigerant leak occur in a different location. It is a decision you must make by weighing the cost of the repairs versus the age of the equipment versus the cost of installing a new coil or air conditioning or heat pump system. If the unit is old and has caused many problems the decision may be easy but it is a big decision so take time and weigh it carefully.

Freon Exposure and Your Health