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Dec 10, 2023

Sleuth the Truth Behind Compressor Failure

The weird thing about compressor problems is that — well, it’s usually not the

The weird thing about compressor problems is that — well, it's usually not the compressor.

"Electric motors, it takes a lot to break them down," said Greg Springer. He is operations manager for Infinity Texas Air in Forney, Texas. "So usually, there's an underlying issue. It could be just age, but you know …"

… It's probably something else. Can the technician on the job today figure out what that something else is? That could determine whether it's a successful call and a happy customer or a visit that appears successful until the new compressor fails (after several additional costs and a lot of frustration).

Even worse, a problem might be compounded — or created in the first place — by previous work that wasn't up to par. Like many contractors, Vincent Eckerson, vice president of operations at Arista Air Conditioning in Long Island City, New York, has run into that.

"We see this, where you have so much oil logging — the whole evaporator's full with oil because there's an oil flow problem, but people just keep putting compressors in. And you know, it's all migrating, locking out. Then the next person comes and puts another compressor on it. And where does all that oil go? It goes right to the coldest spot, where it just sits there."

Raymond Rodriguez, senior service technician for Infinity Texas Air, knows how subtle the underlying culprit can be. He recalls a no-cool call from a customer who had bought her house the previous autumn and hadn't had a need to run the air conditioning until then. Upon initial examination, nothing presented itself.

"Everything was on the money," Rodriguez said. "So I told her, ‘If it happens again, give us a call, but at this point, I’m sorry, everything's working.’"

Sure enough, later that day, she called back. While doing some more digging around, Rodriguez noticed a generic fan motor, not the OEM part.

"I pick up the model number off the condenser and call the manufacturer," he said. "We go over the specs, and it turns out the rpm were way below [what the condenser required]."

Incorrect horsepower, in turn, was causing the compressor to repeatedly overheat and shut off. Proper fan motor installed, problem solved.

Based on the fairly new state of the incorrectly sized fan motor, Rodriguez suspected that when the house underwent inspection before the sale, a home inspector made recommendations to the previous owner. They hired a service company that installed the wrong motor, and then, naturally, nobody noticed until temperatures warmed up the next year.

If a contractor has some history with a customer and the equipment, that can provide a good head start on a call about a bad compressor. Other times, there's no such luck.

As Eckerson succinctly described, what is never a good idea is to just put in the new compressor.

"It's like taking the heart out and then trying to figure out what the pulse was," he said.

Rodriguez begins his process on the verbal side of things instead of the mechanical side, and he works his way around to the outdoor unit eventually.

First, he will get as much basic info as he can from the customer. How long have they lived there? Any other major repairs or refrigerant added in the last six months? According to him, it's a quick effort to understand the environment and what the system has been exposed to.

The next step also takes place inside the house.

"I take a look at the ductwork, check the static pressure on the equipment. Check the filter, the blower wheel, the speed, check the indoor coil," Rodriguez said.

He likes to start on the indoor unit, since any of those components, including a mismatch between ductwork and capacity, can contribute to a compressor's premature demise.

If no obvious suspect is there, then it is on to the outdoor unit. Is the contactor pitted, or does it have any black marks or burn marks? That would be a telltale sign that short-cycling is taking its toll on the compressor.

INSIDE, OUTSIDE: If nothing inside looks off, culprits may wait outdoors. In this case, a welded contactor cause a single phase. PHOTO COURTESY KEVIN COMPASS/HVAC SCHOOL

"After that, I’ll put gauges on the equipment, just to see what my static pressure is," Rodriguez said.

If the refrigerant temperature is close to the ambient temperature, he knows that he is not looking at a no-charge situation. On the other hand, if it's a 90°F day and the standing pressure of the refrigerant for R-22 is showing 60°, more than likely, it's probably a loss of refrigerant.

Eckerson's earlier case of oil logging offers its own hints.

"When you try to blow out all the oil that's there in the suction line and you have a large amount of oil coming out, that means that the compressor has been changed more than once," he said. "Potentially, there may be something on the low side that you need to pay attention to, whether it's poor oil return or something going on with the low side, with airflow causing the oil to migrate to the evaporator."

Springer pointed out that although compressors are pretty tough, even excess grass and dirt can make the outdoor condenser coils dirty enough to make the compressor run at high amps and toward eventual trouble.

"If the starting amps are high on a compressor that is short-cycling — on and off and on and off — that's going to lead to premature failure," he said.

Indoor coils aren't off the hook, either.

Springer observed that if that coil is unusually dirty, all the refrigerant won't be boiling off properly, and liquid will feed back into the compressor. A sneakier problem can arise if the equipment involved has a coil design with two layers of fins.

Springer has seen cases on fairly new units where there might have been some coil cleaning along with a new compressor, but if both layers aren't adequately cleaned up at that time, another failure can follow.

A failed thermostatic expansion valve (TXV) is another suspect. Not metering refrigerant correctly can cause the compressor to overwork. Sometimes it can be slammed shut, Springer noted, which can cause the compressor to fail as well.

And what about that static pressure that Rodriguez mentioned? Springer thinks it is a factor more often than some might expect. In a lot of houses, he said, it's never been measured, so it can mask itself for five or six years.

"And then some people just live with the fact that, ‘Oh, about every seven years, I might have to replace my unit,’" Springer said.

Moreover, the ductwork may be properly sized for the system, but it might involve flex duct in the attic that could run into trouble with humans.

"Somebody could put a box on top of a vent," Springer explained, "or they might step on or smash the duct, and it can throw the whole thing off."

When Infinity Texas Air comes across a compressor that has experienced a burnout from electrical surge or something else, the techs perform an acid test on the refrigerant.

Rodriguez said that in his experience, R-22 is prone to becoming acid in the wrong conditions.

"As far as R-410A, it's very delicate with moisture," he said. "If we come across a compressor that has gone out on 410A and we do the acid test, we always strongly recommend adding the refrigerant even if the acid test was negative, just because it's a synthetic blend."

Rodriguez said that issue can especially come into play when it is 90° or 100° outside.

He encountered a case years ago where the compressor had not failed but wasn't running properly. Rodriguez eventually determined that instead of removing all the R-22, a previous tech had mixed the R-22 with an available synthetic version of it, and that had led to compressor issues.

The electrical side can present its own clues for the attentive tech. Discoloring or fraying on the wires is a starting point. Technicians should be pursuing the point of that overheating, Eckerson said. Is there a loose connection? The location might be surprising.

"I’ve seen line voltage wire on the load side," he recalled, "that was frayed going all the way back because of a loose screw on a contactor. Then it would arc and go all the way back to the compressor."

If Rodriguez has performed all inspections to the point where he is focused solely on the compressor itself, his first step is to take the compressor top off and examine the decompressor harness where it plugs in.

"I would check the harness to see if I’m getting voltage there," he said. "After that, I would ohm the compressor and make sure there's no open windings within the compressor."

Sometimes the tech may find open windings, and Eckerson put a positive spin on that.

"The windings are a safety," he pointed out, "[and if they’re open, then] the compressor did exactly what it was designed to do. It just never reset. But what is causing that? That's the problem."

Back on Rodriguez’ case, in that situation, the compressor may or may not be scorching hot. He will often ask the homeowner for a bag of ice — he puts the ice on the compressor and cools it down with water.

After at least 30 minutes, if the compressor is cool to the touch again, he repeats his tests. If the windings are closed, he will put everything back together, turn the unit back on, and ask the customer if that is their unit's normal running noise.

As a rule of thumb for any compressor replacement, Infinity Texas Air doesn't stop with the compressor. The standard process replaces the run capacitor, the liquid line, and the contactor.

Because the symptom of a compressor failure can point to so many different things throughout an air conditioning system, it doesn't just present a range of potential choice and cost for the customer. It may present an equally wide spectrum of costs and variable profit (or loss) margins for the contractor.

"For us, when we start talking about compressor changes, the idea that our guys are taught is to limit exposure when looking for a potential opportunity," Eckerson said.

The idea is to recognize how a compressor replacement on its own could be a suitable project, but it can potentially cost more than it's worth putting it in, depending on that particular project's associated tasks and time requirements.

Eckerson acknowledged that most techs are essentially problem-solvers. They go to a home to fix a problem.

"But most technicians don't understand the cost of an hour, or the true cost of what a job would be," he said. "How long is it going to take me to actually clean up the systems? The end result after a compressor change and then any refrigerant conversions is something that has to be considered."

At the same time, some customers may understandably be more interested in solely replacing the compressor based on cost at that point than addressing the true culprit. It can be difficult to pinpoint how long that system might hold up afterward, and how to handle that discussion.

Really good companies find a way to address that balance of what will make the most sense for a customer, given the age of a unit and how much additional expense might be required to replace with a newer system as opposed to an isolated fix, Eckerson noted.

"We wouldn't say that we won't do this for you," he explained.

But in a hypothetical case where a new system is an option for an additional 50 or 60 percent more, the idea is also to convey that a new system would probably be a better option for the investment.

Rodriguez said that if techs at his company find an underlying issue, they will generally try to paint the bleakest picture if the customer is not willing to move forward and correct the problem.

Maybe a new compressor on its own in that circumstance buys another few years. Maybe it doesn't.

"We had one job," Eckerson recalled, "where we had moisture in the system and the oil got so gummed up, it looked like snot coming out of the suction line because whoever it was did not do the proper evacuation."

Indeed, no part of a functional system is designed to resemble that. Subsequent moisture buildup and predictable oil breakdown only reinforced how a previous technician failed to do things the right way (and may have let more profitability pass them by in the process).

Don't be in a hurry with standard procedures or evacuation. And as these pros have shown, neither contractors nor customers can afford to look at a compressor problem as a cut-and-dried, get-in-and-get-out proposition.

"Take a look at the telltale signs," Eckerson advised. "Take a look at what you’ve been left with. Because otherwise, the problem will most certainly repeat itself."

Publication date: 3/18/2019

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Robert Beverly has worked in HVAC press for BNP Media since 1998, serving as Engineered Systems' editor before joining The NEWS as a senior editor. In addition to covering legislation/regulatory issues and other assignments, he coordinates and edits Today's Boiler, the official magazine of the American Boiler Manufacturers Association. Robert likes music, the active tense, and air conditioning. Reach him at [email protected].