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I've got a home warranty through Choice Home Warranty and, after multiple attempts to get a service tech out here for my AC unit,they declined the costs of repairing/replacing the unit due to the " compressor failing due to burned out windings"....which they (CHW) said "was not due to normal wear and tear".

My question then is: What causes this to happen in a 14 year old unit?

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    My 3.5 ton unit was installed in June 1991 and still cools, but I have been told that many units are failing at 16 years of service or less. The compressor is original, but the condenser fan motor has been replaced. I don't see how Choice Home Warranty could be sure the failure of yours was not normal wear and tear. – Jim Stewart Aug 3 '17 at 1:03
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    This is the nature of insurance (which purchased warranties are an insurance), they make their money hand over fist for every claim NOT made, and even more for every claim that can be denied. Like @JimStewart is saying, they can't directly tell you its not normal wear and tear unless they can tell you defensibly why it is NOT. So unless it is blatantly obvious, fight it. If its not a prorated credit, get the manufacturers operable life span on the unit and fight fight fight. Call the BBB if it matters, make a stink. Squeaky wheel gets the grease. – noybman Aug 3 '17 at 1:35
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    I agree with noybman. The insurance company is just trying to refuse payment. How can they tell it's not normal if they ever sent someone out to service it? – ArchonOSX Aug 3 '17 at 9:39
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Compressors don't get the luxury of oil changes

You know how the oil in your car breaks down after a while, meaning you have to take your car over to the local quick-lube or up onto the jackstands in your garage and have the oil changed (or do it yourself)? Well, there's oil in your air conditioner too, mixed with the refrigerant, and it breaks down due to heat and traces of moisture just like the oil in your car does. Worse yet, when was the last time your air conditioner got its oil changed?

As a result of this oil breakdown, it turns into an acidic, sludgy substance that has very poor lubricating properties, causing the compressor to work harder. Atop this, the acids attack the insulating varnish in the compressor windings, causing it to break down and lose its insulating ability. As a result, the compressor "burns out", either from being no longer able to spin due to a lack of lubrication or internal shorts in the windings due to the broken-down varnish.

It's possible to catch this ahead of time, by having an HVAC technician use an insulation tester ("megger") to test the integrity of the insulating varnish when the system is commissioned and on a regular basis (such as on a yearly service call) thereafter. The resulting trend readings can predict compressor failures before they happen, and as a result, it's a common practice when maintaining commercial compressors.

Unfortunately, neither insulation tests nor oil changes are part of residential air conditioner maintenance. While changing the oil in an air conditioner requires a pro (it's mixed in with the refrigerant after all, so they have to swap the refrigerant charge out for a fresh one in the process), perhaps having it done every 5 or 10 years would be wise? It'd probably be cheaper than burning through a new compressor every 15 years or so, at least, especially considering that roughly half of compressor failures are due to internal wearout.

  • I assume that refrigeration techs use the same set of gauges on R-22 systems and those with R-410a. Does this cause troublesome cross contamination with the incompatible oils? – Jim Stewart Aug 3 '17 at 9:06
  • @JimStewart -- I would not know.... – ThreePhaseEel Aug 3 '17 at 11:36
  • R410A/R32 are usually different gauges due to the higher pressures. But all the lower refrigerants are pretty much fair game for most people. – Someone Somewhere Aug 3 '17 at 13:02
  • I don't think there would be too much difference in price between new oil and a new compressor. I think you would have to essentially remove the compressor and tip it upside down to get the majority of the oil out... that's a lot of labour. I can't say I've done it or heard of it being done. – Someone Somewhere Aug 3 '17 at 13:10
  • This is to answer comments. I have several sets of gauges 1 set is for POE oil based systems, the other is for older mineral oil systems. Mixing oil is bad news. As far as an oil change most compressors are braised in place if I have a burn out due to acid I remove the compressor, filter/dryer and flush with a product called qwik system flush, this is a huge job for most systems, there is no other way to get all the old oil out of the system in my opinion. After all this when the system is back up and running I will test for acid after several days to make sure the system was clean. – Ed Beal Aug 3 '17 at 13:48
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Every system I have repaired for compressor burn out has lost most or all of its charge. I don't agree with others that say the system needs oil changes. I have serviced HVAC units that were over 30 years old (mineral oil) newer units use Poe or pag oils that attract water close to 200 times that of mineral oil if there is a leak in the system moisture can get in and the moisture in the oil causes the acid formation. Once oil has gone acidic it is tough to fully clean everything out and a new filter/ dryer is needed even after having the system below 500um vacuum for 24 hours A new dryer is needed for a system that has lost its charge and needs to be opened (I haven't seen many keep the system at sub 500 for more than a few hours) Keeping the condensing coil clean (outside coil) keeps the oil from getting overheated and losing the lubrisity if this happens the compressor will start drawing more power and can lead to motor failure. Compressors usually start shutting down because of internal thermal safetys if the oil is burnt from overheat. In both cases the cause is from not being maintained. The condensing coil is easy to keep clean and can be done by a home owner. Knowing the state of charge is a bit more difficult but can be done by taking temperature measurements and verifying the historical values have not changed (for those interested google HVAC super heat ). Last at 14 years the unit probably had R22 I have serviced a few units that only made it 7 years 14 years is not bad if the system never had a recharge ( the most common issue I have found) . With this information you can see how the insurance company used "not being maintained" as there way out of paying a claim as very few people have the knowledge and or are licensed to open a system for maintenance.

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    To properly clean the condenser coils is it sufficient to just hose it down from the outside with a jet of water from a garden hose which is strong but not so strong that it bends fins? – Jim Stewart Aug 3 '17 at 10:34
  • @JimStewart A hose from the outside could just push the debris further into the coil. Ideally, you'd take the top/fan/covers off (depending on unit style) and spray from the inside out. – Someone Somewhere Aug 3 '17 at 13:08
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    I would agree with @him Stewart, rinsing a coil will flush the dust that collects on the fins and improve cooling. I use a product called Nu-bright, it strips the manufacturing oils that collect excess dust and rinse with low pressure. Never use a pressure washer as this will fold the fins over and ruin the coil unless you have hours and fin combs to straighten them if they can be straightened. – Ed Beal Aug 3 '17 at 13:35

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