Air conditioner compressors usually fail because of one of two conditions: time and hours of operation (wear out or abuse. There are some failures that can occur elsewhere in the system that will result in a compressor failure, however, these are more uncommon unless the system has been substantially abused.
Usually abuse is because of extended running with improper freon charge, or because of improper service as you go along. This improper service may include overcharging, undercharging, installing the wrong starter capacitor as an alternative, removing (rather than repairing/replacing) the thermal limiter, insufficient oil, mixing incompatible oil types, or wrong oil, installing the compressor on a system who had a significant burnout without taking proper steps to eliminate the acid through the system, installing a bad compressor (too small) for that system, or installing ACcompressor over a system who had some other failure which had been never diagnosed.
The compressor can fail in just a handful of various ways. It may fail open, fail shorted, experience a bearing failure, or perhaps a piston failure (throw a rod), or experience a valve failure. That is really the whole list.
Whenever a compressor fails open, a wire in the compressor breaks. This really is unserviceable and the symptom would be that the compressor will not run, even though it may hum. If the compressor fails open, and after the steps here does not remedy it, then the system may be a good candidate to get a new compressor. This failure causes no further failures and won’t damage the remainder of the system; if the rest of the method is not decrepit then it might be economical to simply put a brand new compressor in.
Testing for any failed open compressor is simple. Pop the electrical cover for the compressor off, and take away the wires and also the thermal limiter. Employing an ohmmeter, appraise the impedance from one terminal to a different across the 3 terminals in the compressor. Also measure the impedance to the case in the compressor for those three terminals.
You need to read low impedance values for those terminal to terminal connections (a few hundred ohms or less) and you ought to have a great impedance (several kilo-ohms or greater) for all terminals towards the case (which is ground). If the terminal to terminal connections is a very high impedance, you have a failed open compressor. In unusual cases, a failed open compressor may show a minimal impedance to ground in one terminal (which will be one of the terminals associated with the failed open). In this instance, the broken wire has moved and is also contacting the situation. This problem – which is quite rare but not impossible – might cause a breaker to trip and can result in a misdiagnosis of failed short. Be mindful here; do an acid test of the contents of the lines before deciding how to proceed with repair.
When a compressor fails short, what will happen is the fact that insulation on the wires has worn off or burned off or broken inside the shower faucet. This allows a wire on a motor winding to touch something it should not touch – most often itself a turn or two further along on the motor winding. This results in a “shorted winding” that can stop the compressor immediately and cause it to warm up and burn internally.
Bad bearings could cause a failed short. Either the rotor wobbles enough get in touch with the stator, causing insulation damage that shorts the rotor either to ground or the stator, or end bearing wear can allow the stator to shift over time until it starts to rub against the stator ends or even the housing.
Usually when one of these shorts occur, it is really not immediately a difficult short – which means that initially the contact is intermittent and comes and goes. Each and 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. As the short is in place, the existing from the shorted winding shoots up and a lot of heat is produced. Also, normally the short will blow some sparks – which produces acid inside vqxigq ac unit system by decomposing the freon into a combination of hydrochloric and hydrofluoric acid.
As time passes (possibly a few weeks, usually less) the shuddering and also the sparking as well as the heat and the acid cause insulation to fail rapidly on the winding. Ultimately, the winding loses enough insulation that the within the compressor is burning. This may only go on for a couple minutes nevertheless in that time the compressor destroys itself and fills the program with acid. Then the compressor stops. It may at that time melt a wire loose and short to the housing (which may trip your house main breaker) or it might not. In the event the initial reason behind the failure was bad bearings causing the rotor to rub, then usually when the thing finally dies it will likely be shorted for the housing.
If it shorts to the housing, it is going to blow fuses or breakers along with your ohmmeter shows a very low impedance from one or more windings to ground. If it will not short towards the housing, this will just stop. You still establish the sort of failure utilizing an ohmmeter.
You cannot directly diagnose a failed short with the ohmmeter unless it shorts to the housing – a shorted winding won’t show up with an ohmmeter although it would having an inductance meter (but who may have among those?) Instead, you must infer the failed short. One does this by establishing the the ohmmeter gives normal readings, the starter capacitor is good, power is coming to the compressor, Plus an acid test in the freon shows acid present.
Using a failed short, just give up. Change everything, like the lines if at all possible. It is far from worth fixing; it is filled with acid and for that reason is all junk. Further, a failed short might have been initially induced by various other failure within the system that caused a compressor overload; by replacing the whole system additionally you will eliminate that potential other problem.
Less commonly, a compressor will have a bearing failure, piston failure or even a valve failure. These mechanical failures usually just signal break down but tend to 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 are able to signal another failure in the system like a reversing valve problem or perhaps an expansion valve problem that winds up letting liquid freon go into the suction side in the compressor.
If a bearing fails, usually you will be aware as the compressor will sound like a motor having a bad bearing, or it is going to lock up and refuse to perform. Within the worst, the rotor will wobble, the windings will rub on the stator, and you will definitely wind up with a failed short.
If the compressor locks up mechanically and fails to run, you will be aware since it will buzz very loudly for a couple seconds and might shudder (just like any stalled motor) up until the thermal limiter cuts it off. Once you do your electrical checks, you will find no evidence of failed open or failed short. The acid test shows no acid. In this case, you might try a hard-start kit however, if the compressor has failed mechanically the hard-start kit won’t have the compressor to begin. In this instance, replacing the compressor is an excellent plan as long as all of those other method is not decrepit. After replacing the compressor, you need to carefully analyze the performance from the entire system to determine if the compressor problem was induced by another thing.
Rarely, the compressor will experience a valve failure. In cases like this, it is going to either sit there and seem to run happily and can pump no fluid (valve won’t close), or it is going to lock up as a result of an lack of ability to move the fluid out of the compression chamber (valve won’t open). Should it be running happily, then after you have established that there is actually plenty of freon in the system, but nothing is moving, then you do not have choice but to change the compressor. Again, a process with auto that has experienced a valve failure is an excellent candidate to get a new compressor.
Now, when the compressor is mechanically locked up it could be due to a few things. When the compressor is on a heat pump, ensure the reversing valve will not be stuck half way. Also ensure the expansion valve is working; if it is blocked it could lock the compressor. Also make sure the filter is not really clogged. I remember when i saw a system who 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 until the thing was completely filled with liquid. Believe me; that does not work.
Should diagnosis show a clogged filter, then this should be taken as positive proof some failure in the system OTHER than a compressor failure. Typically, it will likely be metal fragments out from the compressor that clogs the filter. This can only happen if something causes the compressor to wear 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 to get in to the compressor on the suction line. This behavior has to be stopped. Look at the expansion valve as well as at the reversing valve (for a heat pump).
Often an old system experiences enough mechanical wear internally that it is “worn in” and needs more torque to start out up against the system load than may be delivered. This method will sound much like one having a locked bearing; the compressor will buzz loudly for a couple seconds then the thermal limiter will kill it. Occasionally, this technique will start right up if you whack the compressor with a rubber mallet while it is buzzing. This type of system is a great candidate for a hard-start kit. This kit stores energy and, if the compressor is told to begin, dumps extra current into the compressor for a second approximately. This overloads the compressor, but gives a little extra torque to get a limited time and it is often enough to make that compressor run again. I actually have had hard-start kits deliver an extra 8 or 9 years in a few old units that otherwise I would have been replacing. Conversely, I actually have had them give just a few months. It is your call, but considering how cheap a tough-start kit is, it is actually truly worth trying once the symptoms are as described.