Air conditioner compressors usually fail due to one of two conditions: time as well as hours of operation (wear out or abuse. There are several failures that can occur elsewhere within the system that can cause a compressor failure, however, these are less common unless the system has been substantially abused.
Usually abuse is caused by extended running with improper freon charge, or caused by improper service as you go along. This improper service can include overcharging, undercharging, installing the wrong starter capacitor as a substitute, removing (rather than repairing/replacing) the thermal limiter, insufficient oil, mixing incompatible oil types, or wrong oil, installing the compressor on the system that had an important burnout without taking proper steps to remove the acid through the system, installing a bad compressor (not big enough) for your system, or installing A/C Compressor on the system who had some other failure which had been never diagnosed.
The compressor can fail in just a few different methods. It could fail open, fail shorted, experience a bearing failure, or a piston failure (throw a rod), or experience a valve failure. That is really the entire list.
When a compressor fails open, a wire in the compressor breaks. This really is unserviceable and also the symptom is the fact that compressor fails to run, though it may hum. If the compressor fails open, and following the steps here will not remedy it, then the system may be a good candidate for a new compressor. This failure causes no further failures and won’t damage the rest of the system; if the rest of the system is not decrepit then it will be affordable to simply put a brand new compressor in.
Testing for any failed open compressor is not hard. Pop the electrical cover for the compressor off, and remove the wires and the thermal limiter. Using an ohmmeter, measure the impedance in one terminal to another across the 3 terminals from the compressor. Also appraise the impedance for the case from the compressor for those three terminals.
You ought to read low impedance values for those terminal to terminal connections (a few hundred ohms or less) and you need to have a superior impedance (several kilo-ohms or greater) for all terminals to the case (that is ground). If any of the terminal to terminal connections is a very high impedance, there is a failed open compressor. In very rare cases, a failed open compressor may show a low impedance to ground in one terminal (which is among the terminals related to the failed open). In this instance, the broken wire has moved and it is contacting the case. This problem – which is quite rare however, not impossible – could cause a breaker to trip and could result in a misdiagnosis of failed short. Be mindful here; do an acid test in the contents of the lines before deciding how you can proceed with repair.
When a compressor fails short, what happens is the fact that insulation on the wires has worn off or burned off or broken inside the Showerhead. This allows a wire on the motor winding to touch something it must not touch – most commonly itself a turn or two further along on the motor winding. This results in a “shorted winding” that will stop the compressor immediately and make it warm up and burn internally.
Bad bearings may cause a failed short. Either the rotor wobbles enough get in touch with the stator, leading to insulation damage that shorts the rotor either to ground or the stator, or end bearing wear can permit the stator to shift down over time until it begins to rub up against the stator ends or even the housing.
Usually when one of those shorts occur, it is far from immediately a hard short – which means initially the contact is intermittent and comes and goes. Every time the short occurs, the compressor torque drops sharply, the compressor may shudder a little visibly as a result, and also this shudder shakes the winding enough to separate the short. While the short is in place, the present with the shorted winding shoots up and lots of heat is produced. Also, usually short will blow some sparks – which produces acid inside vqxigq air conditioning unit system by decomposing the freon into a blend of hydrochloric and hydrofluoric acid.
Over time (possibly a few weeks, usually less) the shuddering and the sparking and also the heat and also the acid cause insulation to fail rapidly on the winding. Ultimately, the winding loses enough insulation the inside of the compressor is literally burning. This may only carry on for a few minutes but in that time the compressor destroys itself and fills the program with acid. Then your compressor stops. It could during those times melt a wire loose and short for the housing (which may trip your home main breaker) or it may not. If the initial reason for the failure was bad bearings causing the rotor to rub, then usually when the thing finally dies it will probably be shorted towards the housing.
If this shorts for the housing, it will blow fuses or breakers and your ohmmeter shows a really low impedance from several windings to ground. When it fails to short for the housing, this will just stop. You continue to establish the sort of failure employing an ohmmeter.
You can not directly diagnose a failed short with an ohmmeter unless it shorts towards the housing – a shorted winding won’t appear with an ohmmeter even though it would with an inductance meter (but who may have among those?) Instead, you have to infer the failed short. One does this by establishing the the ohmmeter gives normal readings, the starter capacitor is nice, power is reaching the compressor, AND an acid test from the freon shows acid present.
With a failed short, just stop trying. Change everything, including the lines if possible. It is really not worth fixing; it is full of acid and therefore is perhaps all junk. Further, a failed short might have been initially induced by a few other failure inside the system that caused a compressor overload; by replacing the complete system additionally you will remove that potential other problem.
Less commonly, a compressor could have a bearing failure, piston failure or a valve failure. These mechanical failures usually just signal degrade but could signal abuse (low lubricant levels, thermal limiter removed so compressor overheats, chronic low freon condition as a result of un-repaired leaks). More rarely, they can signal another failure in the system like a reversing valve problem or an expansion valve problem that winds up letting liquid freon get into the suction side in the compressor.
In case a bearing fails, usually you will know since the compressor will sound like a motor having a bad bearing, or it will lock up and refuse to operate. In the worst case, the rotor will wobble, the windings will rub on the stator, and you will definitely find yourself having a failed short.
In the event the compressor locks up mechanically and fails to operate, you will be aware since it will buzz very loudly for a couple of seconds and could shudder (as with any stalled motor) until the thermal limiter cuts them back. When you do your electrical checks, you can find no proof of failed open or failed short. The acid test shows no acid. In cases like this, you may consider using a hard-start kit however if the compressor has failed mechanically the tough-start kit won’t get the compressor to begin. In cases like this, replacing the compressor is an excellent plan as long as the rest of the system is not decrepit. After replacing the compressor, you must carefully analyze the performance from the entire system to find out whether or not the compressor problem was induced by something else.
Rarely, the compressor will experience a valve failure. In this instance, it is going to either sit there and seem to run happily and definitely will pump no fluid (valve won’t close), or it will lock up due to an lack of ability to move the fluid out of the compression chamber (valve won’t open). Should it be running happily, then when you have established there is indeed lots of freon inside the system, but there is nothing moving, then you certainly have zero choice but to alter the compressor. Again, a system with truck that has had a valve failure is a good candidate to get a new compressor.
Now, when the compressor is mechanically locked up it could be because of few things. When the compressor is on the heat pump, ensure that the reversing valve is not really stuck halfway. Also ensure the expansion valve is working; when it is blocked it may lock the compressor. Also ensure that the filter is not really clogged. I once saw a system which had a locked compressor due to liquid lock. Some idiot had “serviced” the system with the help of freon, and adding freon, and adding freon up until the thing was completely packed with liquid. Believe me; that will not work.
Should diagnosis show a clogged filter, then this ought to be taken as positive proof of some failure within the system Besides a compressor failure. Typically, it will probably be metal fragments from the compressor that clogs the filter. This could only happen if something is causing the compressor to use very rapidly, especially in the pistons, the rings, the bores, and also the bearings. Either the compressor has vastly insufficient lubrication OR (and much more commonly) liquid freon is getting to the compressor on the suction line. This behavior must be stopped. Glance at the expansion valve and also at the reversing valve (to get a heat pump).
Often an older system experiences enough mechanical wear internally that it is “worn in” and requires more torque to start out up against the system load than can be delivered. This method will sound much like one with a locked bearing; the compressor will buzz loudly for a couple of seconds then your thermal limiter will kill it. Occasionally, this method begins right up should you whack the compressor having a rubber mallet while it is buzzing. This kind of system is a good candidate to get a hard-start kit. This kit stores energy and, once the compressor is told to start, dumps extra current to the compressor to get a second or so. This overloads the compressor, but gives some extra torque to get a short time and is also often enough to help make that compressor run again. We have had hard-start kits give me an additional 8 or 9 years in a few old units that otherwise I could have been replacing. Conversely, I have had them give just a few months. It is actually your call, but considering how cheap a difficult-start kit is, it is actually truly worth trying when the symptoms are as described.