The ways that an air conditioner compressor can fail, and what to do about it

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Air conditioner compressors are generally defective due to one of two conditions: hours and hours of operation (wear) or abuse. Some failures can occur elsewhere in the system and cause compressor failure, but are less common unless the system has been extensively used.

Usually, abuse results from prolonged use with inadequate freon charge or consequence of inadequate service en route. This inadequate service may include overcharging, under-charging, installing a bad starter capacitor, removing (rather than repairing / replacing) the thermal limiter, insufficient oil, the mixture of incompatible oils or a bad oil. a major burnout without taking the appropriate steps to remove the acid from the system, install the wrong compressor (too small) for the system, or install a new compressor on a system with another failure that has not never been diagnosed.

may fail only in a handful of different ways. It may break down, fail in short circuit, fail bearing or piston failure (throw rod) or fail valve. It's almost all the list.

When a compressor breaks down, a wire inside the compressor breaks. This is unusable and the symptom is that the compressor is not working, although it can buzz. If the compressor does not open and the following steps do not fix it, the system may be a good candidate for a new compressor. This failure causes more failures and does not damage the rest of the system; If the rest of the system is not decrepit then it would be worthwhile to just put in a new compressor.

The test of a defective open compressor is easy. Remove the electric compressor cover and remove the wires and thermal limiter. Using an ohmmeter, measure the impedance from one terminal to the other on the three terminals of the compressor. Also measure the impedance in the case of the compressor for the three terminals

You should read the low impedance values ​​for all terminal post connections (a few hundred ohms or less) and you should have a high impedance (several kilo-ohms or more) for all terminals to the case (which is the mass). If one of the terminal-to-terminal connections is a very high impedance, you have a faulty open compressor. In very rare cases, a failed open compressor may have a low grounding impedance of a terminal (which will be one of the terminals associated with faulty opening). In this case, the broken wire has moved and is in contact with the housing. This condition – which is quite rare but not impossible – could cause a circuit breaker and trigger a fault diagnosis. Be careful here; make an acid test of the contents of the pipes before deciding how to proceed with the repair.

When a compressor breaks down, what happens is that the insulation on the wires is worn or burned or broken inside the compressor . This allows a wire on a motor winding to touch something that it should not touch – most often itself a lap or two farther on the motor winding. This results in a "short circuit" which immediately stops the compressor and causes it to heat up and burn internally.

Defective bearings may cause a short circuit. Either the rotor wobbles enough to make contact with the stator, which damages the rotor either towards the earth or toward the stator, or the wear of the bearings can cause the stator to move over time until it reaches the stator. what he starts to rub against the ends of the stator or the stator.

Usually, when one of these short circuits occurs, it is not immediately a shortcut – which means that the contact is initially intermittent and comes and goes. Whenever the short circuit occurs, the compressor torque drops sharply, the compressor may quiver a little visibly accordingly, and this quiver shakes enough winding to separate the short circuit. While the short circuit is in place, the current across the short-circuit winding is gaining magnitude and produces a lot of heat. In addition, the short circuit usually produces sparks – which produces acid in the air conditioning system by breaking down freon into a mixture of hydrochloric acid and hydrofluoric acid.

Over time (maybe a few weeks) sparks and heat and acid cause a rapid failure of winding insulation. In the end, the winding loses enough insulation so that the inside of the compressor literally burns. This will only last a few minutes, but during this time the compressor will destroy itself and fill the acid system. Then the compressor stops. It may at this point melt a loose and short wire to the housing (which may trip the main circuit breaker in your home) or it may not. If the initial cause of the failure was a wrong bearing causing the rotor to rub, then usually when the thing eventually dies, it will be short-circuited to the crankcase

If it runs to the crankcase, it will blow fuses and / or circuit breakers. Your ohmmeter will show a very low impedance of one or more windings to ground. If it is not short to the case, it will just stop. You always define the type of failure using an ohmmeter.

You can not directly diagnose a short circuit with an ohmmeter unless it runs to the case – a shorted winding will not appear with an ohmmeter with an inductancemeter (but which has any of those?) Instead, you must infer the failed shorts. You do this by establishing that the ohmmeter gives normal readings, that the start capacitor is good, that the power is coming to the compressor AND that an acid test of the Freon shows the present acid.

With a failed short circuit, give up. Change everything, including lines if possible. It is not worth repairing. it is full of acid and so is all junk food. In addition, a failed short circuit could have been initially induced by another system failure that caused the compressor to overload; by replacing the entire system, you will also get rid of this other potential problem.

Less often, a compressor will experience bearing failure, piston failure, or valve failure. These mechanical failures generally indicate premature wear but may indicate abuse (low lubricant levels, thermal limiter eliminated, compressor overheating, chronic Freon condition due to unrepaired leaks). More rarely, they may report another failure in the system, such as an inversion valve problem or an expansion valve problem that eventually leaves the liquid freon entering the suction side of the compressor.

the compressor will look like a motor with a bad ride, or it will crash and refuse to operate. In the worst case, the rotor will flicker, the windings will rub on the stator and you will end up with a failed short circuit.

If the compressor hangs mechanically and does not work, you will know it because it will buzz loudly for a few seconds and may quiver (like any engine stalled) until the thermal limiter cuts it off. When you perform your electrical checks, you will find no evidence of failure or failure. The acid test will show no acid. In this case, you can try a hard starter kit, but if the compressor is faulty, the starter kit will not start the compressor. In this case, replacing the compressor is a good plan as long as the rest of the system is not decrepit. After replacing the compressor, you should carefully analyze the performance of the entire system to determine if the compressor problem was caused by something else.

Rarely will the compressor fail the valve. In this case, it will either sit there and seem to work happily but will not pump any fluid (the valve will not close), or it will lock due to the inability to exit the fluid from the compression chamber (the valve will not be closed). open). If it works well, then once you have established that there is actually a lot of freon in the system but nothing moves, then you have no other choice than to change the compressor. Again, a system with a compressor that has had a valve failure is a good candidate for a new compressor.

Now, if the compressor is mechanically locked it could be due to a number of things. If the compressor is on a heat pump, make sure the reversing valve is not stuck halfway. Also make sure the regulator is working. If it's stuck, it can lock the compressor. Also make sure the filter is not clogged. One time, I saw a system that had a compressor locked because of the liquid lock. An idiot had "maintained" the system by adding freon, adding freon, and adding freon until the thing was completely full of liquid. Believe me; it does not work.

If the diagnosis shows an obstructed filter, this should be considered as positive evidence of a system failure OTHER than a compressor failure. Typically, it is the metal fragments of the compressor that clog the filter. This can only happen if the compressor is used very quickly, especially in pistons, rings, bores and bearings. Either the compressor has a very insufficient lubrication OR (and more commonly) the liquid freon enters the compressor on the suction line. This behavior must be stopped. Look at the regulator and the reversing valve (for a heat pump).

Often an old system suffers enough internal mechanical wear to be "worn out" and require more torque than the system load. This system will look like a locked bearing; the compressor will buzz loudly for a few seconds, then the thermal limiter will destroy it. From time to time, this system will start straight if you hit the compressor with a rubber mallet while it's buzzing. Such a system is a good candidate for a difficult starter kit. This kit stores energy and, when the compressor is told to start, discharges the extra current into the compressor for a second or two. This overloads the compressor, but gives extra torque for a short time and is often enough to run this compressor again. I had difficult starter kits giving me an extra 8 or 9 years old in some old units that I would have otherwise replaced. Conversely, I had them give only a few months. This is your call, but considering the cost of a difficult starter kit, it is worth trying when the symptoms are as described.

And that is, in summary, what can happen to an air conditioner compressor and what you can do about it.

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Source by Jim Locker

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