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I just had the capacitor on my air conditioner fail. It was explained to me that the reason for this was the oil inside the capacitor got too hot, expanded, made the whole thing bulge, and no more cool air or spinning fan.

Is this is a "all parts wear out" thing? Or can misuse of an AC unit cause this sort of problem? Or can other things being wrong with the AC unit cause this sort of problem?

The main question I'm trying to answer is: How can I avoid this in the future?

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When exactly was the air conditioner built? – Compro01 Aug 8 '13 at 14:25
@Compro01 I'm not sure, it came with the house. It's an XE 1000 if that helps track things down. – Alan Storm Aug 8 '13 at 14:53
When did you get the house? Did the guy mention whether the capacitor had been replaced before? – Compro01 Aug 8 '13 at 16:11
@Compro01 You give me too much credit :) I bought the house three and a half years ago, if there was a mention of the capacitor it's been lost in the mists of time and paperwork. – Alan Storm Aug 8 '13 at 16:32
I was meaning whether the guy who did the repair mentioned if it had been replaced before. – Compro01 Aug 8 '13 at 17:05

5 Answers 5

up vote 7 down vote accepted

The life of electrolytic capacitors is primarily shortened by heat. Therefore ambient temperature, temperature of nearby motors, ventilation and air circulation (e.g. fan), presence of thick layers of dust, clogged grilles, excess paint, ... can be important factors.

Electrolytic capacitors are manufactured to various specifications:

  • Capacitance: e.g. 1 uF, 10000 uF
  • Voltage (maximum) e.g. 5V, 400 V
  • Lifetime e.g. 1000 hours at 80 C, 1250 hours at 150C
  • Operating Temperature e.g. 40-85, 25-150 C

By choosing a capacitor that suits your operating conditions you can ensure that you get the maximum life.

As with many things, some manufacturers produce good quality products and some low-cost manufacturers simply lie about their products' specifications. Choosing the right manufacturer may have a large influence on operational lifetime.

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According to what I can find, the XE1000 line was manufactured from about 1994 until about 2006.

If it was made in 2000 or later, it may be a victim of the capacitor plague.

Some background : From about 2000 until about 2008, various Taiwanese electronics parts manufacturers produced water-based aluminum electrolytic capacitors containing a flawed electrolyte formula. Specifically, the formula lacked the phosphate corrosion inhibitors needed to protect the aluminum anode. Without the inhibitors, instead of a stable layer of protective aluminum oxide on the anode, you instead get a buildup of aluminum hydroxide. The reaction producing that aluminum hydroxide buildup also produces hydrogen gas. Capacitors have vents to deal with that gas (as the hydroxide reaction happens even with the inhibitors, but at a much lower rate), but eventually, the rate of the reaction grows to a point where the vent is not able to vent the gas as quickly as it is being produced. The pressure then builds up to the point where the capacitor seals or casing bulges or even outright bursts. This obviously wrecks the capacitor. This failure tends to happen after about 2-3 years under most circumstances.

From about 2002 til 2010, vast numbers of computer components and other electronics suffered failures due to these capacitors. Dell initiated a recall and spent hundreds of millions of dollars replacing these capacitors which were used on the motherboards of many models of their computers and many other manufacturers implemented similar measures.

If this is the case, the failed capacitor has probably been replaced at least once before, and replaced with another such capacitor, which then failed again.

Alternatively, if it was one of the earlier units, the capacitor may simply have reached the end of its lifespan, as RedGrittyBrick suggests. Under typical conditions, a typical quality non-defective electrolytic capacitor has a lifespan of about 20 years.

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Wow, that's super interesting (or maybe I'm weird and find this historical stuff interesting). Thanks for the lesson! – Alan Storm Aug 8 '13 at 17:38
One thing though -- "capacitor plague" issues only affected low-ESR electrolytics used in electronic circuits, primarily switching power supplies. It did not have any bearing on motor start capacitors (which are more closely related to large electrolytics used for linear power supply filtering) or motor run capacitors (which are large film capacitors). – ThreePhaseEel Jun 24 at 2:35

If the replacement capacitor seems to solve the problem then there is not much you can do. The capacitor can fail because the motor is getting old and takes more to start, small twig blocked the motored and stalled, surge/voltage spike (either from the line or bad motor's back-emf), or just it failed/life expectancy was reached.

Tl;dr, in my experience, fluke or fading motor, worth the cost of a cap or two to make sure before replacing motor/unit.

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as a HVAC technician. i found most failed capacitor issues was involved with blocked/dirty condensate coils, causing the compressor/fan to drew more amperage. so check first your condensate (outside unit) coil. if it is dirty unscrew the grill/fence around the unit and clean it with water. it is sometimes important to use detergents to wash it off.

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Capacitors (similar to light bulbs) will fail at some point. Sometimes the chemicals (an electrolyte/oil/etc..., though PCB are very stable) will degrade and cause the capacitor to expand (perhaps blow up). Other times, the dielectric material (the material that separates the two conductors in the capacitor) will degrade, allowing the terminals of the capacitor to short together (perhaps causing the capacitor to blow up). Many air conditioner capacitors have a "feature" that causes the capacitor to become disconnected when they expand, reducing the chance of explosions.

The lifetime of the capacitor is greatly impacted by temperature and voltage. At higher temperature and higher voltage, the capacitors will fail more quickly. The temperature can be influenced by dust and debris (insulating the capacitor) in the compressor unit. The voltage should be OK, except for transients like lightning strikes. Also, keep in mind that that dirty coils/improper charges will cause the system to be less efficient and run for a longer amount of time each day. This will cause the capacitor fail at an earlier date since it's being used more heavily.

Air conditioners often will have two capacitors: "start" and "run". These have slightly different requirements, but for the purposes of this post can be considered to be equivalent.

There are two main technologies used for the creation of capacitors for air conditioners: electrolytic and polypropylene film.

Electrolytic capacitors are more sensitive to temperature and have a propensity to expand, causing premature failure. Polypropylene capacitors generally are more temperature-resistant AND can self-heal. When polypropylene capacitors have an internal short, they tend to just vaporize the local area, leaving the rest of the capacitor to function normally.

Some datasheets of polypropylene capacitors I found state that 90-94% of the capacitors will last >=60,000 hours. Electrolytic capacitors are often used as "start" capacitors and are only used for a short time (on the order of a second) each time the AC unit turns on. They are often rated for on the order of 40,000 starts.

So, if you want a longer life capacitor in the future, keep your air conditioner unit clean and well maintained, and use polypropelyene capacitors, if possible. Also, you could install a whole-house surge suppressor in order to reduce power supply surges.

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