Why Do Residential HVAC Compressors Fail?

June 12, 2018
Solving the mystery is like an episode of 'CSI: Compressor Scene Investigation.' by Michael Robertson, LG Electronics, USA

The hallmark of a good residential HVAC system is reliability. That begins and ends with the system’s components. At the heart of this system is a compressor, which, when installed and maintained properly, can last well beyond its warranty.

From engineering and design to sourcing and manufacturing, compressors today are being built better than ever to meet and achieve performance goals, efficiency standards and reliability expectations.
Yet, on occasion, things do go wrong. And when they do, the experienced team of engineers at LG’s compressor quality lab in Texas wants to know about it. This group has performed enough post-mortems on compressors to star in a series called "CSI: Compressor Scene Investigation."

Our quality lab has generated a ton of interesting information over the years, but this might be the biggest shocker: most compressor fatalities aren’t related to the manufacturing or design of the components. According to our lab, there’s almost always an undetected killer still lurking in system ready to claim another compressor.

So what’s actually causing residential HVAC system failures? To help service technicians find the true culprit hiding in the cooling system, LG’s compressor engineering team has gathered some useful insights to help identify and remedy the root causes of system failures. Implementing these simple checks into your HVAC service calls will help your contracting business stand apart from competitors who address air conditioning problems with guesswork.

Resist the ‘Charge it’ Mentality
According to our lab, the number 1 cause — by far — of compressor failure is a lubrication issue due to lack of oil. Overcharging is the most likely culprit because refrigerant floodback causes the oil to wash out of the compressor.

Of course, there are a number of legitimate reasons to add a refrigerant charge to an HVAC system, but, based on our lab’s findings, there are several potential HVAC system issues you should check first.

Poor Airflow
The first suspect a service technician must cross off the list is airflow. Poor or restricted airflow is top reason a system might appear undercharged.

There are thousands of scenarios that could lead to restricted airflow in a system. As a former technician, I can recall one job where we discovered that a paper wrapper was blocking almost three-fourths of the evaporator coil. It had apparently been sucked into the ductwork and never discovered — until after it had claimed two compressors that probably worked fine all along.

The point of the story is that it’s critically important that a service technician thoroughly inspect the system for any air restrictions or collapsed ductwork before assuming compressor failure.

Any experienced “compressor coroner” will tell you that underperforming ductwork is a significant problem in the HVAC industry today. But, because it’s usually tucked away in crawl spaces or attics and difficult to access, it’s easy to dismiss poor airflow as a potential problem.

When there’s not enough air available to evaporate the refrigerant, the air conditioning system doesn’t pick up enough heat, which means excess liquid refrigerant can flood back into the compressor and cause damage. This problem is easily compounded by adding refrigerant to a system that’s been ducted too small.

Don’t assume that the ductwork is satisfactory. It’s simply not true in many cases. sometimes a system appears undercharged, but in reality, it is not getting enough airflow because of ductwork

Although it’s time-consuming, checking airflow can provide a lot of answers. There’s no doubt it’s an important skill and, in many cases, critical to the reliability of the system and the life of the compressor.

Matched Systems
HVAC manufacturers spend tens of millions of dollars to design and build today’s holistic systems that work together to deliver cooling comfort and energy efficient performance.

When components that weren’t designed for each other get paired together, homeowners may notice a decline in performance, inefficiency and ultimately even failure.

For instance, a mismatched evaporator can lead to reliability problems if a modern, high-SEER outdoor unit is installed on an evaporator not designed for that unit.

When diagnosing an HVAC failure, you should make sure the system components were properly matched. It’s more important than ever for performance, efficiency and reliability.

Metering Devices
If you’ve already determined the airflow is adequate and the system is matched, it’s time to check the metering device. The TXV always needs to be operating properly and, if it’s an orifice pin device, the pin should be sized for the indoor-outdoor combination. Sometimes the pin in the evaporator needs to be exchanged with the pin shipped with the outdoor unit depending on the combination. Always consult the manufacturer’s engineering data to be sure the correct pin is deployed.

(And while you’re checking on the system, look to see whether the system is using a capillary tube-equipped evaporator. This equipment should be upgraded because the older capillary tube technology can create problems for modern systems.)

Suction Line Sets
There are two checks a technician should review relating to the suction line sets. First, make sure there are no kinks or irregularities in the suction line set. Even a small kink could provide the misleading appearance of an undercharge in the system.

Technicians should also review the manufacturer’s recommended line set size. The difference between a 1-1/8-in. suction line and a 7/8-in. could harm the compressor. A system with improperly-sized suction lines may also operate at a lower SEER and capacity ratings and even experience oil return problems.

HVAC Maintenance
Finally, ask the homeowners about their HVAC maintenance habits. Regular filter replacement is vitally important to the health of a home cooling system. In homes, where air filters haven’t been changed in months — or years — a clogged air filter can contribute to premature compressor failure.

Technicians should also look around the home for indoor vent closures.

Many homeowners still believe (wrongly) that they’re saving energy by closing air vents in unused areas of their home. In reality, they may be shortening the life of their HVAC compressor. Modern, high-efficiency cooling systems are designed to operate for a specific square footage. The blockage created by closed vents forces systems to work harder, which over time could lead to product failure.

Too Little Refrigerant
Though it’s easier to spot, a system with too little refrigerant can also create severe wear on a compressor. In these cases, the discharge temperature rises excessively, breaking down the oil and causing damage to the pumping mechanism.

Don’t Automatically Blame the Compressor
The best thing a technician can do for themselves and their customers is to accurately weigh in a refrigerant charge.

Any time you find persistent system problems, including compressor failure, weigh in the refrigerant charge based on the manufacturer’s rating plate. If the system still presents as undercharged, resist the urge to add more refrigerant and look deeper for some of the problems mentioned above.

The Bottom Line
Here’s the bottom line: what looks like “compressor failure” often has nothing to do with compressor quality or performance at all. Still, some technicians might misdiagnose the problem and replace the most expensive part. That’s like putting a new engine in a car the first time you hear a noise— costly and needless.

Consider that a large percentage of compressors sent to LG’s quality lab because of a suspected product issue show no signs of failure whatsoever. When tested, they worked perfectly!

The ultimate irony is that it’s become more difficult and costly to replace a compressor these days. Outdoor units of yesteryear were small, and it was easier to change compressors. Today, units are much larger with much higher efficiencies, and replacing a compressor can be a major ordeal.

So, as trained technicians star in their own episodes of CSI: Compressor Scene Investigation, remember not to waste time and money chasing the wrong suspect. In many cases, the compressor isn’t guilty. The real culprits are often found elsewhere.

Michael Robertson is Senior Account Manager for LG Electronics USA Component Solutions, in Alpharetta, Georgia.