How long do evaporator coils last in a home AC system?

Assuming aluminum; corrosion will likely be the biggest problem . Air with the normal 0.04 % CO2 is acidic. Any other gases like hydrochloric , bleach vapor,etc, will also absorb on the wet coils in the AC season adding to corrosion ( No problem during the heat season.) . Keeping the coils clean helps ; you can help keep them clean by using " better" filters and changing them every couple months in the cooling season ( when the coils are wet). I have changed filters more often than most and I have used a spray cleaner on the coils; now have 20 years of service . The first compressor died at 8 years and the second compressor now has problems ( Houston area so lots of heat and humidity ). PS : I just replaced the first evaporator at 24 years, no leaks . Got a whole new system . We have replaced the good type filters about every 2 months ; as @ Karl K says, it is about keeping them clean. ( Houston area so the 5 ton AC runs a lot).

I am a Texas Licensed HVAC contractor own my own company in Katy, Texas.

I have worked on, repaired and replaced countless evaporator coils over the years not to mention AC condensers, furnaces and so on. I have been in this industry for over 23 years.

There have always been problems with Freon leaks. There WILL always be problems with Freon leaks... Puron too if you have a system that uses that refrigerant.

Air conditioning is a mechanical piece of equipment. There is a fallacy in thinking it should last 15 - 20 years with no problems. Certainly you may be fortunate, but it's not the norm.

So why then is there this big too do about Freon leaks all of a sudden? Because back in the late 90's and early 2000 time period, Freon was cheap. Systems were not very efficient and many didn't require that much refrigerant as the more efficient models do today (2017) In fact it is quite possible your system may hold 10 pounds or more. In some cases as much as 20 pounds.

Back in the late 90's and early 2000's it typically cost around $100 to 150 to recharge a AC system. Can't do that today, because cost of refrigerant is through the roof. You must fix the leak. If you can't afford to fix the leak, every recharge is going to drain your wallet.

Many times to fix the leak, replacement of some of your HVAC equipment may be required. This is why there is a fallacy thinking that HVAC systems should last 15-20 years with hardly ever a problem. People just used to ignore the problem because the cost to fix it for a time via recharging was reasonable cost, that now the cost is no longer reasonable.... due to higher refrigerant costs.

AC systems have always leaked, but because of high costs of repair and refrigerant -- this problem has gotten your undivided attention.

The HVAC industry is big on selling you gimmicks -- like it's hard to stop a Trane. I can tell you right now, that AC train will stop dead in it's tracks without Freon / Puron. It really makes no difference to single out Trane other than to show case the gimmick that they regularly provide. Every manufacturer suffers from the same problem.

This is why you need a pro to minimize your AC problems. Even this is no guarantee... but you stand a far better chance of less trouble than using unskilled labor to constantly repairing your AC system.

Coil Life
I'm not sure if how long they "should last" matches most home owners experiences. Looking at many consumer complaint websites showed many users with failure between 5 and 7 years.

Recommended Maintenance Didn't Save Me
You should always do the recommended maintenance, but in my case maintenance wasn't the problem. I have a 14.5 SEER, 2.5 Ton Carrier unit. The evaporator coil started leaking after 43 months (under 4 years). It was a small leak where the copper met the rusty metal housing. I used high quality filters and replaced them every 2-3 months. They never looked dirty but I still replaced them within the recommended window. It was under a service contract and had preventative maintenance done by a licensed tech from AC-Designs in Central FL every 6 months (twice a year).

The parts were under warranty but labor was not so it was a little over $600 to replace with a 90 day labor and 1 year parts warranty. The tech did note that my case was unusual and he's seen both extremes with some lasting the life of the system (15+ years).

One thing he mentioned on replacement is some replacements are aluminum based evaporator coils vs the copper in hopes of a longer life. I don't know which is better but I found this article about copper vs aluminum here.

Depending on the system, sometimes it makes more since to replace the whole system. Get quotes on each (preferably by 2 or more vendors) before you decide.

The department of energy has some other great info on AC systems here.

They should last for the life of the A/C system, which is generally 15-20 years for a high quality system. (Many people end up replacing their systems between 12 and 15 years due to efficiency issues or deferred maintenance causing damage to more easily damaged components, such as the compressor.)

Most of the time, evaporator coils fail because they are allowed to get dirty or are allowed to have ice build up on them. Things you can do yourself to help prolong the life is to make sure you change your HVAC intake filter regularly and use a high quality filter (filters should be in place for no more than a month, and should be replaced sooner in a dusty environment if you can no longer see light through the filter), and make sure that your evaporator coils are draining correctly.

The easiest way to make them last longer is to have a licensed HVAC technician perform regular maintenance on your system. This should be done once a year, typically in the winter time. The technician will clean the coils and check them over. At the same time, the A/C tech will check to make sure that your coolant is at the right level/pressure and that there are no leaks in your system.

If you replace them, you probably want to replace the entire system at this point thanks to many recent gains made in efficiency.