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Freon Leaks & Evaporator Coils

Refrigerant used for cooling has come to be known by DuPont's trade name which is Freon.

My experience with Freon leaks has been entirely with refrigerants R-22 and R-12 used for household and automotive cooling. This article deals mostly with R-22, but touches briefly on the new refrigerants.

  Old Freon New Freon
Automotive AC R-12 R-134a
Household AC R-22 R-410a

Old Freon (R-22 or R-12) is homogeneous, and will always maintain its chemistry, whether charged as a liquid or as a gas.

These refrigerants are "forgiving." They allow considerable variation in the refrigerant charge. For that reason, small leaks can be tolerated for up to twelve months. It has been common practice, since the advent of air conditioning, to add a little Freon each spring, and then cool for another season.

Finding and Fixing Freon Leaks

Large Freon leaks not only make you lose your kool, but can also lead to freeze-ups. (As the Freon pressure falls, so does the freezing temperature.) Location and repair of refrigerant leaks is a challenging assignment—not for amateurs. You need a repairman who:

  • Is experienced & capable
  • Is patient
  • Is trustworthy
  • Has good judgement

Repairing a Freon leak can be as simple as replacing a valve core or tightening a fitting. It can be as expensive as replacing an evaporator coil, condenser coil, or copper line set.

In this article, I will concentrate on finding and fixing Freon leaks—not on the environmental issue. (That is covered in The Ozone Layer Crisis … .) The ultimate goal is to kool your home with a minimum of repair expense and disruption to your routine.

If your AC is low on Freon, it's because it leaked out—you don't burn the stuff. So where did it go? Here are some possible sites for leakage: valve cores, weld joints, shipping valves, rusted filter canisters, or the copper tubing itself. I estimate that 70% of time, the leakage is in the evaporator coil, and 10% of the time, new valve cores are needed.

Improved AC Efficiency

For about 20 years, the AC industry has been under pressure from both environmental and conservation groups. To improve efficiency, the industry started rifling the interior of the copper tubes that go into the cooling coil. They create spiral grooves, and that causes turbulence in the flow of Freon as it changes from a liquid to a gas. The result is a remarkable increase in cooling efficiency.

Unfortunately, rifling introduces stress concentrations that become points where cracks can form and propagate. The entire industry has found a dramatic increase in the failure rate of their coils. Some customers experience repeat failures, while others have zero problems.

In 1995, I installed in my home and my duplex, a total of three systems (including the coils). Since then, neither system has developed a Freon leak. On the other hand, I have customers with repeat failures. Charles had 4 coil failures in twelve years. Mary had 4 coil failures in eight years. Eleanor had 5 coil failures in 15 years. I personally have documented the evidence.

A Most Hostile Place

Cooling takes place in the evaporator coil, and for this reason some very hostile forces are at work. There are hurricane force erosive winds where the liquid is changing to a gas.

In the off cycle, the coil temperature might be as high as 140F. In the cooling mode, temperatures approach freezing. The result is a thermal cycling gradient of about 100°F.

Dissimilar metals are used in the construction of the coil—copper, steel, and solder alloy. The result is a slightly corrosive cell.

In summary, you have erosion and thermal cycling, along with an electrolytic cell. Added to these, you have stress concentrations introduced by the rifled tubing.

This combination ultimately leads to coil failure. That's why (my estimation) 70% of Freon leak problems can be corrected by replacing the evaporator coil.

Unfortunately, it's not uncommon to pay $1000 or more for a new coil installation.

Freon 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.

If the leak is big enough, we use soap bubbles. Sometimes you can actually feel a breeze from the leaking Freon. Some technicians use ultrasonic.

The Black Light Method

The most revealing technique for locating Freon leaks is for the technician to install a liquid tracer into the system, and allow it to circulate about two weeks. The tracer will ooze out the leak openings.

He will then shine a special (black) light onto the copper tubing. I've seen dozens of Freon leaks in a single evaporator coil—and all in the finned area, away from any bend or weld joint.

When All Else Fails

What if the leak is in the copper tubing—in a wall or buried in insulation? That usually requires a pressure test, and the solution is to replace the line set.

Dealing With the Situation

So what does that mean to the homeowner? If a coil has truly failed, it must be replaced immediately. But sometimes there's a tiny leak in some remote spot that cannot be easily located.

The technician will use different techniques to find and repair leaks, but ultimately his concern is how quickly the Freon is escaping. A technician may come out each spring, and add a lb. of Freon, rather than subject his customer to an expensive repair job.

Furthermore, if he replaces the evaporator coil, he might have to come back in a couple of years, and replace it again. After he replaces the same coil again and again and again, he looks for answers, and sometimes the answer is to just add a little Freon each spring.

If you have a leak-free AC system, you are fortunate and blessed.

Summary and Conclusion

Finding and repairing Freon leaks can be tedious and expensive. But, for traditional R-22 or R-12 Freon, if the loss is small, most people just live with the situation, and add some refrigerant each spring.

At a certain point, it has to be fixed. Some technicians keep an ongoing record of suspicious AC systems, and each spring evaluate the situation. Excessive Freon loss is the first red flag. If a technician has to come back in the middle of summer, that's a huge indicator the leak or leaks have grown, and must be dealt with soon.

Furthermore, you cannot assume there's a single leak. For different reasons, people are stressed by Freon leaks, but all the wishing in the world won't put a stop to them.

Talking About Wishing

As a repairman, I wish the manufacturers would stop rifling the interior of copper tubing used in evaporator coils. That would drastically reduce the number of Freon leaks, and make my job easier. But, I can't imagine them doing that. The increased efficiency is so dramatic, they will continue to live with the side effects.

Evaporator Coil Warranties

Most AC manufacturers give a 5 year warranty on their coils. Some companies extend the warranty to 10 years when you replace a system or a condenser/coil match up. At most, your contractor will give a one year labor warranty. If you've been adding Freon, and your coil warranty is about to expire, that's an ideal time to have your AC contractor do some thorough testing for Freon leaks. I hope this article helps you better deal with this difficult situation.

Where We've Been—Where We're Going

Since 1992, the government began forcing the auto manufacturers to convert from R-12 to R-134a. The conversion is pretty much complete, and we're now starting to see the results. Since 2006, the AC industry began converting home cooling systems from R-22 to R-410a. Beginning in 2010, it will be illegal to manufacture R-22 equipment.

The Worst is Yet to Come

I see a multitude of problems with the new R-410a systems which are explained in AC—Only for the Rich?, but this article is about evaporator coils that leak refrigerant. The coil pressure for a typical R-22 situation is 240 psi. The same R-410a situation will require a coil pressure of about 360 psi.

For both applications—R-22 and R-410a—manufacturers are using the exact same coils, but different metering devices. We've had significant Freon leaks in coils for 20 years. What will happen when the same coils are subjected to a pressure that's 50% higher?

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