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Hey guys, here's a question for you: why is it that compressor replacements are often done on commercial refrigeration and HVAC systems with apparently acceptable results, while compressor replacements on home HVAC systems are somewhat frowned upon due to the claimed high failure rate of replacement compressors?
 

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Not a HVAC guy but the compressor was replaced on my heat pump and that unit lasted another 10-12 yrs. I also had the compressor replaced on a rental although we sold it a yr or so later.
 

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It's primarily due to the fact that there are people doing work that are not qualified and do not have the proper equipment.

Good practice requires the repairman to have a vacuum pump of sufficient capacity to reach 100 microns and a micron gauge to know when he reaches the required vacuum that removes all the alien gasses and moisture from the system.

If the compressor failed due to an actual burnout of the electrical winding, it is necessary to install a suction line filter at the very least. That's just a few of the areas where some jack-legs fail.

They may even overcharge the system and you'll be paying lots more for power than you should. Speaking of overcharging, they're likely doing that to you as well, considering what you're getting for your money!
 

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Hey guys, here's a question for you: why is it that compressor replacements are often done on commercial refrigeration and HVAC systems with apparently acceptable results, while compressor replacements on home HVAC systems are somewhat frowned upon due to the claimed high failure rate of replacement compressors?
Compressors normally don't die prematurely unless they're murdered. The compressor is pretty much the most reliable component in any refrigeration/ac system.

Low airflow, dirty coils, mismatched components, incorrect charge failing txvs can ruin compressors.

If the underlying problem is not corrected, the next one fails too.

Bad repair practices surfer brought up can also cause problems - have it over-charged and liquid can return to the compressor and kill it. Compressors are vapour/gas pumps only.
 

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A 7.5 ton commercial A/C is a bit more expensive than a 4 ton residential A/C. So the cost benefit is different.
 
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after 10 year warranty period compressor replacement is silly - put well over $1000 into a unit and have the evap coil spring a leak a few years later, another few hundred to over one thousand dollars which could have gone towards a new unit.
 

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Yes, liquid slugging of a compressor will damage it. Usually it will bend the reed valves so they no longer seat properly. Even a small overcharge on an orifice regulated system can reduce the system superheat to the point where a small amount of liquid enters the compressor crankcase and washes the lubrication from the bearings and rings. Compressors are pretty robust but they aren't bullet proof. I have seen several cases where liquid slugging actually broke the connecting rod in the compressors. You'd think it would make the compressor run very noisily but these were 2 cylinder compressors and instead it causes a telltale vibration like no other. They actually all continued to work albeit at reduced capacity. These we factory mistakes that didn't have the accumulator that should have been installed in their particular application.

As for improper evacuation, some of the supposed service techs have told me they don't need a micron gauge since they can tell by looking at their charging manifold gauge, that shows pounds per square inch, when the vacuum is pulled deep enough. That's sort of amusing since an absolute pressure reading that would support a 100 microns column of mercury would be shown as 0.0019336777871316 psi on their gauge. They must have exceptional eyesight and even better powers of perception than I do.

Any oxygen or moisture left in a system will be like poison and will kill the compressor prematurely. We used to pump the refrigerant R-11 in liquid form through burnouts but with the advent of better suction line filters and tougher restrictions on dumping any refrigerant into the environment, the suction filter is now used almost exclusively to clean up a particulate contaminated system. A good quality SLF can also trap the acids that are produced in the system that caused the compressor to fail in the first place. Those acids were created due to improper evacuation. For example, take some oil vapor (which has sulphur in it), add some water vapor and expose it to oxygen at the high temperatures, such as at the discharge of the compressor, and you can produce sulphuric acid.

Now we have been full circle and arrived back at the jack-leg who dummied up, either at the factory or when doing a repair from failure due to other reasons. His work methods sometimes make another premature failure almost assured.

I watched a service tech replace the unit on my neighbor's heat pump a couple years ago. I wanted to manually apply some Darwinian action to him and rid the world of such ignorance. I engaged him in small talk, nothing about refrigeration, yet he broached the subject and succeeded in outlining how technical his line of work was and how it took special training to be able to do it. He said there was good money in it if you're good at it. I think that last part is the only aspect of refrigeration work that he actually knew well. :wink2:

So to make a really long answer short (too late now) the second failure is often the repairman's fault. Vet them and ask if they plan on using a micron gauge. Then watch them to see that they do.
 

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Compressors are usually killed rather then die of old age. And the “high rate of failure” is often just a sales tool. Systems can be rebuilt, modified and put together over and over again with completely acceptable results.
But that said-

Commercial equipment is usually more of a financial investment for the customer. The equipment is also usually more expensive to install, with cranes and other requirements to get the equipment in place.

Commercial equipment is usually built a bit more stout then residential.

Some commercial/industrial equipment simply can’t be removed without knocking down walls and taking out doorways. Compressors and other parts fit through doors (usually).

Emergency repairs can be done much quicker then emergency replacement. When your walk in freezer grenades a compressor at 5:00 on Friday night with $25,000 of product inside, it’s a whole lot quicker to acquire and install a compressor then a whole new system.

Some commercial and industrial equipment is purpose made for its job. So when the equipment fails there simply is no replacement system to install. It must be built from scratch.
 
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