Think Your AC Isn’t Working Properly? It Could be a Refrigerant Leak

Most of the time someone calls and reports that the air conditioning is not working properly. By checking system pressures and temperatures, you can determine whether the system refrigerant charge is either low or empty. Refrigerant leaks typically fall into four types:
  1. Standing Leaks: occur even while the unit is tuned off
  2. Pressure Leaks: occur at a certain pressure
  3. Vibration Leaks: occur when a strain is put on a line or component
  4. Temperature Leaks: occur as a result of the expansion and contraction caused by temperature change
One way to start checking for a refrigerant leak is to listen to the system. Most of the time it will be hard to hear any gas escaping because equipment noise is too loud or the leak is too small.

Next, visually inspect the system. Since some oil (lubricant) circulates throughout the refrigeration system along with the refrigerant, inspect the system for signs of oil leaks.

Some obvious places to look for leaks are service valve caps, brazed fittings, and piping joints. It is easier to check the low-pressure side of the system while the system is off. The system pressures will equalize, making the pressures on the low-pressure side higher than when the system is running. The high-pressure side of the system is the exact opposite; it should be checked while the system is operating because the pressures will be higher than when the system is turned off.

Types of Detection Equipment

There are various types of leak detection equipment. Some detectors require an electrical source to plug into, others are battery operated, and still others use both energy sources. Some detectors have flexible sensing devices for use in hard-to-reach places, while others are inflexible. You must choose the detector that is correct for your application and situation. 

The five main types of leak detection equipment are:
  1. Soap bubbles
  2. Electronic leak detector
  3. Halide leak detector
  4. Ultrasonic leak detector
  5. Ultraviolet leak detector

Soap Bubbles

Soap bubbles are typically the simplest and most inexpensive method of leak detection. Some soap bubbles are more sensitive than others, so remember to compare the contents. When a suspected leak area is located, liquid soap solution is applied. If a leak is present, soap bubbles will appear. In many cases, a different leak detector of some form is used to narrow down the area of a possible leak. From there, soap bubbles may be applied to pinpoint the exact location of the leak.

Electronic Leak Detector

Many electronic leak detectors are available on the market, and their efficiencies vary. Some are capable of detecting as little as half of an ounce of lost refrigerant per year. All electronic leak detectors use an element that is sensitive to halogenated gases. An audible and/or visual alarm signals when a leak has been detected. Some electronic detectors will not pick up a leak in newer refrigerants (HFCs) because of their chemical composition, so consult the manufacturer of the detector to find which refrigerants each device can detect.

When checking for leaks, air drafts should be kept to a minimum. Consequently, the leak detector tip should be moved slowly. Check lowlying areas around the equipment because most refrigerant is heavier than air, and will settle in low areas. Most detectors will have various sensitivity level settings, such as low, medium, and high, which can be used when measuring for a known leak. In some cases a small pump inside the detector draws in air across the sensing probe to facilitate detection of refrigerant.

Halide Leak Detector

A halide leak detector typically uses acetylene or propane gas. After ignition, the flame from this gas heats a copper disc. Attached to this bottle of gas is a hose that is used as a sniffer to check for leaks. As the hose is moved, air is drawn through it and into the burner of the detector. When a leak is detected, the flame will change to a greenish color. A halide leak detector is dangerous to use in confined spaces or flammable areas. Never use a halide device to check a system that contains a highly flammable refrigerant because an explosion could occur. Certain refrigerants will break down when exposed to the flame and cause phosgene gas, which is poisonous.

Ultrasonic Leak Detector

The ultrasonic detector locates ultrasonic sounds that are emitted when a gas leaks from a system. These ultrasonic sounds are sometimes hard to hear either because of surrounding noises or because the leak is so small. To overcome this problem, the systems technician can wear a headset. One benefit of this type of detection is that it picks up sound waves from the gas, which does not have to be a refrigerant gas. This makes it possible to pressurize a system with nitrogen without using a refrigerant as a tracer gas. Money spent on an ultrasonic detector is well spent because of its versatility. It can detect sounds from other equipment, such as a leaking steam trap or ductwork leaking air.

Ultraviolet Leak Detector

With the ultraviolet leak detector, a fluorescent additive is circulated throughout the refrigeration system. In most cases, plenty of time (sometimes up to 24 hours) must be allowed for the dye to complete its course. An ultraviolet light is then used, which will reveal a fluorescent glow emitted around any leaks. In some cases, a dye that does not involve an ultraviolet light is used. With either option, the building engineer should consult the compressor manufacturer to ensure that the dye will not harm the compressor and thus void any warranty.

This article is adapted from BOMI International’s course Refrigeration Systems and Accessories, part of the SMA® and SMT® designation programs. More information regarding this course or the High-Performance certificate courses is available by calling 1.800.235.2664. Visit BOMI International’s website,


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