What causes a/c evaporator coils to leak? We have found this to be the most common problem plaguing air conditioners. To explain this, we first need to bust a common air conditioner myth.
A Common A/C Myth
Many homeowners believe that, over time, an air conditioner uses refrigerant. Maybe a long, hot summer leaves a perfectly good air conditioner “winded” and low on refrigerant. We just need to tune-up the a/c and top-up the coolant, right? In reality, an air conditioner or heat pump has a sealed refrigerant system that should never “use up” or run out of refrigerant. The coolant or refrigerant is only the medium used to transfer heat from the inside of the home to the outside. The only resource that is expended is electricity.
If the refrigerant is not consumed in the process of cooling your home, then it must be lost only by a leak in the copper tubing. For many years, the air conditioning industry has used copper tubing to harness the pressure of refrigerant and bring comfort to the masses. Copper is soft and abundant, and easy to seal in the field with solder or brazing alloy. If copper is such a good material, why do we see so many coolant leaks? Is this due to poor field connections, poor manufacturing, or is there a third possibility?
Trane Looks for the Root Cause of Refrigerant Leaks
A number of years ago, Trane began a study to determine the true cause of this constant threat to our comfort. As service technicians, we have noticed that leaks from field or factory connections cause problems in the first year and are fairly rare. The problem leaks that develop in a 4 – 7 year old air conditioner occur in the copper tubing wall not the connection points or braze joints. The source of these pre-teen leaks is what the Trane engineers set out to find in their study.
Our technicians have noticed that certain brands of air conditioners develop leaks faster than others and that the newer, more efficient air conditioners are more prone to leaking than the old energy hogs. The reason for this seems fairly obvious to Cincinnati HVAC contractors. A/C manufacturers can raise the efficiency of their equipment by using thinner copper in their evaporator coils. Heat transfers faster through the thinner copper, but this efficient tubing also leaks sooner. One could argue that the legislation that raised the minimum efficiency of air conditioners and heat pumps to 13 SEER resulted in thinner tubing walls, more evaporator coils leaks, and, as a result, more ozone-damaging R-22 released into the atmosphere.
The Real Cause of Refrigerant Leaks
So we know that thinner tubing develops leaks sooner, but what is causing the refrigerant leak in the first place? The leaky a/c coils that the Trane engineers studied had microscopic pin holes seemingly drilled throughout the coil tubing. Trane’s in-home studies revealed that the culprit was formic acid. Formic acid was corroding the copper and drilling these tiny pin holes. The acid penetrates the thinner, high-efficiency tubing faster and is making some air conditioner brands look very bad. But where is the formic acid coming from? Isn’t that what gives fire ants their sting? What is formic acid doing in our homes and on our air conditioner coils?
Is Formaldehyde the Culprit?
Formaldehyde in the home can convert into Formic acid on the a/c coil. It is extremely mild, but over a period of 5 years, it will produce pinholes in copper tubing. We call this process formicary corrosion, and it is the main reason that we still buy R-22 by the skid. If you have researched indoor air quality, you’ll know that formaldehyde is a major pollutant in our homes. An infamous case of severe formaldehyde in the living space was the FEMA trailer provided to Katrina victims. While less severe than a FEMA trailer, most homes have a measurable amount of formaldehyde in the indoor air, and this will always cause formicary corrosion and leaks. Unfortunately, no amount of air conditioner maintenance will prevent leaks. We can, however, reduce the amount of formaldehyde in your home with indoor air quality upgrades.
The Cure for A/C Refrigerant Leaks
Stop using copper to manufacture cooling coils. The photos above show copper and aluminum coil tube walls subjected to a formic acid corrosion test. Trane has found that aluminum is not susceptible to formicary corrosion. Through great feats of science and manufacturing genius, Trane began production of an all-aluminum air conditioning coil in 2005. Since then, we have installed many Trane all-aluminum coils, and we have yet to see a single leak in the tubing walls due to formicary corrosion. This truly is an amazing track record. We believe this makes Trane the only reasonable choice for your next air conditioner.
Comparison of Trane coil and typical copper coil after a 500 hour salt spray test.