What Actually Kills an Air Conditioner

Ask what kills air conditioners and you will get opinions. There is field data, though it is older and thinner than the question deserves, and it repays careful reading because it separates two things people routinely conflate: what breaks and what ends the equipment.

511 failed residential systems

The oldest of the three, from 1978, examined 511 failed residential air conditioners and sorted them by cause:

• 31% simple electrical failures — the most common reason for a service call
• 17% refrigerant problems — recorded as true failure and replacement
• 14% compressor failure
• 12% failed outdoor fans

A 1987 survey of 492 heat-pump dealers found a similar shape: 19% refrigerant leaks in failed units, 16% failed compressors or motors, 12% other mechanical components. Both are quoted in the Florida Solar Energy Center's 2018 field study.

And a 1998 analysis of roughly 6,000 rooftop-unit service records — quoted in NREL and Purdue's fault prioritization report — found 14.2% of major faults were electrical, 3.6% fan-motor degradation and 2.1% condenser fouling, while noting that the most costly were compressor failures.

The pattern across all three

Electrical faults dominate the service call. A contactor, a capacitor, a relay — cheap, frequent, fixed in an afternoon. But look at what the surveys record as true failure and replacement, and refrigerant problems sit at 17% and 19%, the largest single named cause in both.

That gap between the two lists is the useful part. The most common fault is not the most consequential one. A dead capacitor announces itself immediately and gets fixed. A slow refrigerant leak announces nothing at all, runs for years, and eventually presents as a compressor.

How long they actually last

The most recent and most careful of the field data comes from Fenaughty and Parker at the Florida Solar Energy Center, who monitored 46 homes over four and a half years. Median compressor age in the population was nine years, which in a stationary population implies a typical service life of about 18 years — close to industry estimates.

But that average conceals the interesting half. Twelve of the 46 systems were replaced during the study, at a median age of 13.5 years, with a very rapid drop-off in survival beyond 15 years. The measured failure rate was 7.0% per year.

So the population splits. Some systems reach eighteen years and beyond. Others leave four or five years early. The same study found operating hours were a significant predictor of shorter life — which is the thread connecting this to the fault data above, because faults are what add operating hours.

What this does and does not tell you

It tells you where to look. If refrigerant problems account for a fifth of true failures, and if the systems that die early are the ones running the most hours, then charge condition is worth knowing about long before anyone notices a comfort problem.

It does not tell you how many years any particular fault costs. None of these surveys measured that, and as we have written elsewhere, nobody else has either.

Read the dates, and the citations

Two of these surveys are from 1978 and 1987. Equipment has changed since — scroll compressors, variable speed, different refrigerants, higher efficiency mandates. We quote them because they are the field data that exists, and because the 1998 and 2018 work points the same direction, not because a 1978 failure distribution should be assumed to hold today.

We also hold both older surveys as quoted in the 2018 Florida review, rather than from the original ASHRAE Transactions papers. That is a real limitation. We would rather flag it than let a secondary citation read as a primary one, and the original references are listed below so you can go further than we have.