Service Clinic: Best Methods for Refrigerant Leak Detection

by Paul  Flora

The most common you may encounter as a Service Technician, arranged in groups are:

• CFC Chlorofluorocarbon R-12, R-502 (Phased out)
• HCFC (Hydrochlorofluorocarbon) R-22, R-401A, R-401B, R-402A, R-402B, R-408A, R-409A (In phase out)
• HFC Hydrofluorocarbon R-134a, R-404A, R-407C, R-410A, R-438A, R-507.

Current EPA regulations recommend and/or require leak detection and repair when it has been determined that a system is losing refrigerant. The EPA will soon release new rules governing the handling and leak detection of R-410A as well as other leak rate criteria changes that will make good leak detection practices even more important. Accurate leak detection methods must be utilized to find leaks in a system and correctly address them. The following are the accepted methods of HFC leak detection.

Soap Bubbles/Visible Method
Works with all refrigerants. It is very accurate for pinpointing a leak.

Fluorescent Dye/Visible Method
Works with all refrigerants. The dye must be added to refrigerant, and a special UV light is required.

Electronic Leak Detectors
Currently the most popular method in use. These detectors will work with all refrigerants. They can be very accurate or very inaccurate, depending on sensor condition. They must be checked regularly against a calibrated reference leak to ensure accuracy.
The various electronic leak detectors are covered below. The information is not meant to steer you towards or away from any technology, but is for information purposes only.

Ultrasonic
Uses sound amplification. Acts on the high frequency sound pitch that occurs when gas passes through an orifice. This method may not be accurate on small leaks because not enough sound is generated through a small orifice.

Corona Discharge
Air is pulled through an energized electrical field around an electrode. Refrigerant gases are broken down by the electric arc (corona discharge) and detected by the sensor. The presence of a detectable gas changes the current flow in the electrode and triggers an alarm. Gases other than refrigerant can trigger an alarm, giving the appearance of a leak when there may not be one (false alarm). The sensor may degrade over time and need to be replaced. It should be checked regularly against a calibrated reference leak to ensure correct operation. Do not use in the presence of combustible gases.

Heated Diode
Air is pulled over a heated diode. Halogenated gases are broken down by the heater resulting in a change in current flow through the diode. The change in current through the diode triggers an alarm. The heated diode sensor is sensitive to excess refrigerant in addition to other contaminates such as moisture and oil resulting in sensor degradation. Because of sensor degradation, the heated diode sensor must be checked regularly for accuracy and replaced within 100 hours of use. When exposed to contamination including excess refrigerant, the sensor could fail much more quickly. For this reason, sensors must be checked regularly against a calibrated reference leak to ensure correct operation. Do not use in the presence of combustible gases.

Heated Electrolyte
Air is pulled over a heater that is in the presence of an electrolytic material that reacts with the broken down halogenated refrigerant gasses.
Halogenated gases result in a change in current flow between the heater electrode and the electrolyte which triggers an alarm. Like the heated diode sensor, the electrolytic sensor is sensitive to excess refrigerant and other contaminants resulting in sensor degradation. Excess refrigerant exposure can have a quick impact on sensor life.
A heated electrolyte detector must be checked regularly with a calibrated reference leak to ensure that it can accurately detect a refrigerant leak. Do not use in the presence of combustible gases.

Infrared
Air is pulled through an optical window in the infrared sensor. Refrigerant gases absorb IR Radiation. The optical sensor senses this and triggers an alarm, depending on how much IR has been absorbed. This technology is very accurate and has been the technology of choice in lab settings for many years.
It has only recently (last 5 years approx.) been introduced to the field in the form of portable hand held leak detectors. The refrigerant isn’t broken down by heat and doesn’t directly contact the sensor, thus the sensor isn’t subject to contamination. Sensor life expectancy is over 1000 hours or the life of the leak detector. To ensure
accuracy, the infrared detector should be checked regularly against a calibrated reference leak.

Electronic Leak Detectors
Designed for use with HFC refrigerants, no matter what sensor type is utilized, when properly maintained (including sensor replacement when necessary), all work very well. Some are more susceptible to contamination — including exposure to excess refrigerant — than others. For this reason, never open a bottle of refrigerant and place the pickup tube in the refrigerant stream, as it can quickly ruin the sensor in your leak detector. Always use a calibrated reference leak to determine the accuracy of your sensor. cfm Distributors, Inc. has official calibrated reference leak devices available that attach directly to a jug of refrigerant and provide a leak reference equal to 5 grams (0.18oz) per year. These cost less than $195 to purchase and are required for ensuring an accurate leak detector and test method. If your leak detector will trigger on the reference leak, it’s capable of finding any leak in the system you are checking. If not, replace the sensor.

Some electronic detectors act on the total concentration of refrigerant gasses, others act on a change in the concentration of refrigerant gasses. It’s important that you know what type meter you are using and how to correctly use it. Most sensor instruction manuals recommend moving the pickup tube over the unit being checked at a rate of 1-in. to 3-in. per second. If it triggers, make note of where it started and where it stopped. Reverse direction and again note the start and end points of detector notification. The leak should be midway between the trigger points. Never camp on a suspected leak as your detector will automatically zero and quit picking up the leak until you move away for a few seconds to let the detector re-establish a new zero point.

After determining the general area of a leak with the use of an electronic detector, soap bubbles is a great method of pinpointing the exact location of the leak.