Now that the weather has become a bit more seasonal we might as well continue our air conditioning discussion as warm weather will return. So far we've discussed the air conditioning evaluation and service as well as refrigerant recovery. To review these last articles click HERE. In this installment on air conditioning I'd like to discuss leak detection.
Good leak detection involves patience, understanding, and sometimes a measure of perseverance. In a fast paced world filled with waiting customers, the next profitable job, and impatient service advisors, refrigerant leak detection often gets far less attention than it deserves. The customer is ultimately the individual who pays the price (quiet literally) for this.
Leak detection methods include liquid UV chemical detectors, electronic leak detectors (aka "sniffers" wink , spray bottles of soapy water, visual inspections, and vacuum pumps. Each method has its proponents and its detractors. Some are very effective, others not so much. By far the most popular method of leak detection is the use of chemical UV dyes, where a dye is inserted into the refrigerant system by itself, mixed with a small charge of refrigerant, or with a light quantity of refrigerant oil. A black light and/or special goggles are used to see the dye glowing at the leak location.
Technicians like dye because it is easy to use, can be seen visually in most cases, and is relatively inexpensive. When using dye it's important to consider how the dye is being injected into the system, how much refrigerant is already present in the system, and if any oil is being added with it. Too much dye or too much refrigerant oil can cause system inefficiencies.
Using leak detection dye has one small drawback however. It takes time to work. This may not mean anything to a technician who can move on to the next profitable job, or next customer, but it does mean something to the customer who is now asked to drive their vehicle around and return to the shop to have the leak evaluated. Inconvenience is the biggest reason customers strongly dislike having their vehicle worked on. So what to do?
First checking the air conditioning system with an electronic leak detector may yield faster results and avoid having the customer return to the shop once again for leak evaluation and then potentially a third time to have parts installed. Electronic leak detectors have a poor reputation in many repair shops. Their reputation as not being accurate is derived from poor maintenance practices, a poor understanding of how the tool works, and a lack of diligence in using the tool. Electronic leak detectors are extremely accurate tools that are specifically made for detecting hydrocarbons. However they can be very finicky to operate and must be well maintained.
When using a leak detector the technician must be sure to move the sensing probe very slowly in the area of a potential leak. As refrigerant is heavier than air, it is important to move the sensing tip of the tool underneath sources of potential leaks as well. The tip of the tool should never contact any components and must be kept very clean. This is very important! Any contamination of the sensing tip will render the tool inaccurate, or inoperative. Many electronic leak detectors contain filters, desiccant, or moisture traps that need to be maintained periodically. Not performing regular maintenance on your electronic leak detector will also render it less accurate.
Electronic leak detectors can be very useful for hard to detect leaks such as those from an evaporator core. Leak detection dyes can be difficult to use in locations such as evaporator cores because of ease-of-access issues. Utilizing an electronic leak detector can lead to a faster, more accurate diagnosis.
When using an electronic refrigerant detector to find possible leaks at the evaporator core, the technician should turn the AC system on medium high with the windows and doors of the vehicle closed and let the system run for 5 to 10 minutes. Next, shut the blower motor off and leave the doors closed for 5 minutes. If the evaporator core is leaking, the refrigerant will slowly build up in the heater box. Checking for a leak with an electronic leak detector at the evaporator box drain hose while this is happening can find some leaks, while opening the door and placing the sensing tip at the vent with the blower on low speed can help identify other evaporator leaks. In either event, you won't be able to effectively use leak detection dye to properly identify an evaporator leak.
The three other methods I mentioned initially (visual inspection, soapy water, and vacuum testing) each have their place, but are not the first method to turn to. Vacuum testing has a solid reputation, but is only accurate for larger leaks and does not pinpoint a leak. Soapy water also works for larger suspected leaks but unlike vacuum testing a system, must be utilized with the system running.
A visual inspection must always be performed to confirm the presence of aftermarket parts, potential collision damage, or areas of concern. With the oils used for R12 systems, leak areas often collected much dirt and would build up sometimes large displays of road grime. R134a PAG oils don't collect nearly as much debris, and as such make visual detection much more difficult. It is still worth doing a visual inspection however.
When it comes to leak detection the preferred method should always take into account the amount of time the vehicle will be at the repair shop, potential for customer inconvenience, and likely effectiveness. A combination of visual inspection, electronic leak detection, and UV leak detection dye will yield an effective diagnosis while minimizing customer inconvenience.
Until next time, keep up the good work, never stop learning, and sign up below to be informed each time I post an article. I can always be reached at www. intelligentmechanic.com for questions, comments and concerns.
deadpansolace9706 Community Member 
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