Air conditioner compressors usually fail due to one of two conditions: time and hours of operation (wear out), or abuse. There are some failures that could occur elsewhere within the system which will cause a compressor failure, but these are less common unless the internal system continues to be substantially abused.
Usually abuse is known as a result of extended running with improper freon charge, or because of improper service along the way. This improper service may incorporate overcharging, undercharging, installing the wrong starter capacitor instead, removing (as an alternative to repairing/replacing) the thermal limiter, insufficient oil, mixing incompatible oil types, or wrong oil, installing the compressor on an system that had a major burnout without taking proper steps to remove the acid out of your system, installing the improper compressor (not big enough) for the system, or installing a fresh compressor on an system that had another failure that was never diagnosed.
The compressor can fail in exclusively some other ways. It may fail open, fail shorted, have bearing failure, or maybe a piston failure (throw a rod), or have valve failure. That's just about the entire list.
Whenever a compressor fails open, a wire contained in the compressor breaks. This is often unserviceable and also the symptom could be that the compressor will not run, though it may hum. When the compressor fails open, and following the steps here won't fix it, probably the system might be a good candidate for a new compressor. This failure causes no further failures and should not damage the remainder of the system; in case the rest of the system is not decrepit in that acse might possibly be economical to simply create a new compressor in.
Testing for a failed open compressor is easy. Pop the electrical cover for compressor off, and take away the wires and also the thermal limiter. Using an ohmmeter, measure the impedance from a place terminal to a different one across all three terminals of a typical compressor. Also measure the impedance towards the case of the compressor for all those three terminals.
You should read low impedance values for those terminal to terminal connections (several hundred ohms or lower) and you ought to have a high impedance (several kilo-ohms or greater) for all terminals into the case (that's ground). If any of many terminal to terminal connections is an high impedance, you have a failed open compressor. In very rare cases, a failed open compressor may show a low impedance to ground to the next terminal (which is able to be one of the terminals associated with the failed open). In such cases, the broken wire has moved and is contacting how it is. This condition - and that is quite rare though not impossible - could cause a breaker to trip and could result in a misdiagnosis of failed short. Be careful here; do an acid test of a typical produce in the lines before deciding the best way to proceed with repair.
Each time a compressor fails short, what happens is the idea that insulation in the wires has worn off or burned off or broken inside the compressor. This allows a wire on an motor winding to the touch something it should't touch - most likely itself a turn or two further along at the motor winding. This brings on inside of a "shorted winding" which can stop the compressor immediately and cause it to get hot and burn internally.
Bad bearings could potentially cause a failed short. Either the rotor wobbles enough to contact the stator, causing insulation damage that shorts the rotor either to ground or to the stator, or end bearing wear can allow the stator to shift above time until it begins to rub contrary to the stator ends or the housing.
Usually when such a shorts occur, this is not immediately a hard short - therefore initially the contact is intermittent and comes and goes. Every time the short occurs, the compressor torque drops sharply, the compressor may shudder a lttle bit visibly subsequently, and such shudder shakes the winding such that you could separate the short. While the short posesses place, the present in the shorted winding shoots up as well as a lot of heat is produced. Also, usually the short will blow some sparks - which produces acid contained in the air conditioner system by decomposing the freon right into a mixture of hydrochloric and hydrofluoric acid.
Eventually (possibly a very few weeks, usually less) the shuddering and the sparking as well as the heat as well as the acid cause insulation to fail rapidly on your winding. Ultimately, the winding loses enough insulation that the surrounding the compressor is literally burning. This can only keep on for a few minutes however in at that moment the compressor destroys itself and fills the machine with acid. Probably the compressor stops. It may at that time melt a wire loose and short to the housing (which can trip your house main breaker) or towards the. If the initial cause of the failure was bad bearings causing the rotor to rub, then usually in the event the thing finally dies it is shorted towards the housing.
Whether it shorts to the housing, it will blow fuses and/or breakers with your ohmmeter will show an extremely low impedance from one if not more windings to ground. Whether or not this does not short to the housing, and then it will just stop. You still establish the type of failure using an ohmmeter.
Do not directly diagnose an unsuccessful short with an ohmmeter unless it shorts to the housing - a shorted winding won't come up who has an ohmmeter while it would having inductance meter (but who has just like some of those?) Instead, you should infer the failed short. You attempt this by establishing the the ohmmeter gives normal readings, the starter capacitor is great, power is arriving along at the compressor, AND an acid test of the freon shows acid present.
By using a failed short, just give up. Change everything, including the lines if possible. It's not worth fixing; its packed with acid thus is all junk. Further, an unsuccessful short happens to be initially attributable to other failure in the system that caused a compressor overload; by replacing the whole system you furthermore may will look to lose that potential other problem.
Less commonly, a compressor are going to have bearing failure, piston failure or perhaps a valve failure. These mechanical failures usually just signal tire but could signal abuse (low lubricant levels, thermal limiter removed so compressor overheats, chronic low freon condition from un-repaired leaks). More rarely, they often signal another failure within the system say for example reversing valve problem or perhaps an expansion valve problem that winds up letting liquid freon get into the suction side of many compressor.
Should a bearing fails, usually you'll be safe in the knowledge for the reason that compressor will seem like a motor by using a bad bearing, or it will lock up and refuse to run. In the worst case, the rotor will wobble, the windings will rub in the stator, and you may wind up by using a failed short.
When the compressor locks up mechanically and fails to run, you'll be safe in the knowledge since it will buzz very loudly for a couple of seconds and will shudder (very much like any stalled motor) so that the thermal limiter cuts it off. After you do your electrical checks, you will discover no clue of failed open or failed short. The acid test will show no acid. In this instance, you would possibly consider a hard-start kit however if the compressor has failed mechanically the hard-start kit won't have the compressor to start. In such cases, replacing the compressor is an effective plan long as the whole system is not decrepit. After replacing the compressor, you must carefully analyze behavior the entire system to determine whether the compressor problem was induced by something different.
Rarely, the compressor will experience a valve failure. In this instance, it'll either sit there and appear to operate happily but pump no fluid (valve won't close), or it should lock up due to an inability to maneuver the fluid out from the compression chamber (valve won't open). If it is running happily, then when you have established that there is indeed a lot of freon inside the system, but nothing is moving, after this you have no choice but to alter the compressor. Again, a system by using a compressor which includes had a valve failure is an efficient candidate for only a new compressor.
Now, when the compressor is mechanically locked up it could be as a result of the only a few things. In the event the compressor is present in a heat pump, check to see if the reversing valve will never be stuck halfway. Also be certain expansion valve is working; if it's blocked it can lock the compressor. Also be certain filter is not really clogged. I once saw a system that had a locked compressor from liquid lock. Some idiot had "serviced" sst by adding freon, and adding freon, and adding freon before thing was completely full of liquid. Trust me; that doesn t work.
Should diagnosis show a clogged filter, then this is necessary as positive evidence of some failure throughout system In addition to a compressor failure. Typically, it will likely be metal fragments out of the compressor that clogs the filter. This might only happen if something is generating the compressor dress in very rapidly, particularly in the pistons, the rings, the bores, and also the bearings. Either the compressor has vastly insufficient lubrication OR (and many more commonly) liquid freon starting to get into your compressor in the suction line. This behavior must be stopped. Look at the expansion valve and at the reversing valve (for only a heat pump).
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Often air conditioner compressor cost a not-needed system experiences enough mechanical wear internally that it is "worn in" and demands more torque to start contrary to the system load than can be delivered. This method will sound just like a car battery a locked bearing; the compressor will buzz loudly for a couple seconds later the thermal limiter will kill it. Occasionally, this method will kick off right up if you happen to whack the compressor which has a rubber mallet although it is buzzing. Such a system is a superb candidate for only a hard-start kit. This kit stores energy and, whenever the compressor is told to do start, dumps extra current into the compressor for a second or thereabouts. This overloads the compressor, but gives some extra torque to have a short period of time which is often such that you could honor that compressor run again. We have had hard-start kits give me an additional 8 or 9 years in most old units that otherwise I would personally seem to have been replacing. Conversely, I even have had them give only a few months. It is your call, but considering how cheap a hard-start kit is, its worth trying while the transmissions for sale symptoms are as described.
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