Troubleshooting Ride-Along: I Was Told My AC Compressor Is Bad — Is It?
Sometimes a service call turns into an estimate.
This time, an estimate turned into a service call.
The homeowner in Palm Coast called us because their AC wasn’t cooling. Another company had already been out and diagnosed the problem.
Bad compressor.
That’s a big diagnosis.
A compressor is one of the major components of an air-conditioning system, and depending on the age and condition of the equipment, a failed compressor can absolutely turn into a repair-versus-replace conversation.
In this case, the homeowner had apparently already reached that point.
They weren’t calling us to troubleshoot the AC.
They were calling us for an estimate to replace it.
Fair enough.
Except we were standing in front of the allegedly dead air conditioner anyway.
Might as well see if the compressor knew it was dead.
Customer Complaint
Technically, this was supposed to be an estimate.
But the original customer complaint was:
“My AC isn’t cooling.”
So we went back to the beginning.
What is it doing—or not doing?
The system wasn’t cooling.
Okay.
When did this start?
Had it gradually been cooling worse?
Did it suddenly stop?
Was the indoor fan running?
Was the outdoor unit doing anything?
Did anything happen around the time it stopped?
And then, of course, we had another important piece of history:
“Another company already looked at it. They said the compressor is bad.”
That’s useful information.
But somebody else’s diagnosis doesn’t automatically become our diagnosis just because they got there first.
And we weren’t going to quote an entire replacement system without at least looking at the air conditioner sitting in front of us.
We Don’t Diagnose the Other Guy’s Diagnosis
This is important.
A second opinion shouldn’t begin with:
“Let’s prove the other company wrong.”
That’s not troubleshooting.
But it also shouldn’t begin with:
“They already diagnosed it, so let’s assume they’re right.”
We start over.
The customer has an AC that isn’t cooling.
Okay.
Why isn’t it cooling?
If we arrive at the same diagnosis, great.
If we don’t, that’s useful too.
We’re interested in what the equipment is actually doing today.
A Compressor That Isn’t Running Isn’t Necessarily a Bad Compressor
This distinction can save somebody a tremendous amount of money.
The compressor isn’t magic.
It requires electricity.
It requires the appropriate controls to tell it to operate.
And that electricity has to make it through several components before the compressor can do anything.
So if we find a compressor sitting there doing absolutely nothing, we haven’t diagnosed:
Bad compressor.
We’ve diagnosed:
Compressor isn’t running.
Those aren’t the same thing.
Now we need to find out why.
So We Started Troubleshooting
We had a call for cooling.
Now we needed to determine what was happening at the outdoor equipment.
Was proper voltage available?
Was the contactor being energized?
Was the contactor actually closing?
Was power making it through the contactor?
Was the compressor receiving the voltage it needed?
Were the electrical components testing properly?
We followed the electrical path.
And eventually we found the problem.
It wasn’t the compressor.
It was the contactor.
What the Heck Is a Contactor?
Think of the contactor as a heavy-duty electrical switch inside your outdoor AC.
Your thermostat isn’t directly turning that big compressor on and off.
Instead, the low-voltage control circuit tells the contactor:
“We need cooling.”
The contactor closes.
That allows high-voltage power to reach the compressor and condenser fan.
When the cooling call ends, the contactor opens again.
It does this over and over and over throughout the life of the air conditioner.
Eventually, contactors can fail.
And if the contactor doesn’t properly deliver power to the equipment?
The compressor isn’t going to run.
Not because the compressor is dead.
Because it isn’t getting what it needs to operate.
What We Found
On this Palm Coast system, the contactor had failed.
That meant the compressor that had previously been diagnosed as bad wasn’t actually being properly powered.
We corrected the electrical problem.
Then came the interesting part.
The allegedly dead compressor started.
Well.
Good news.
The compressor had made a miraculous recovery.
😂
Except, of course, it hadn’t.
There was nothing miraculous about it.
It hadn’t been the failed component in the first place.
The Estimate Became a Service Call
This is the opposite of another Ride-Along we’ve written.
On that call, we started with a service call and found a nearly empty air conditioner installed during the Clinton administration.
After diagnosing it, we decided that continuing to spend the homeowner’s money repairing that system didn’t make much sense.
So the service call became a free replacement estimate.
This one went the other direction.
We arrived expecting to quote replacement equipment.
Then we discovered the existing AC had a repairable electrical problem.
So instead of selling the homeowner a new air conditioner…
the estimate became a service call.
We replaced the failed contactor and got the existing system operating again.
That’s a considerably different invoice.
Why Didn’t We Just Trust the Previous Diagnosis?
Because we were being asked to sell somebody an air conditioner.
That’s a pretty good reason to make sure they actually need one.
And again, this isn’t about attacking another technician.
We weren’t there when the original diagnosis was made.
We don’t know exactly what they saw, what they tested, what happened during their visit, or how they reached their conclusion.
We’re responsible for our diagnosis.
If we’re going to tell a homeowner:
“Your compressor has failed,”
we want measurements and testing that support that conclusion.
Especially when that diagnosis could lead directly to replacing the entire system.
How Do You Actually Determine Whether a Compressor Is Bad?
There’s no single test for every compressor failure.
That’s part of the problem with diagnosing one simply because it isn’t running.
Depending on the situation, we may need to determine:
Is the compressor receiving proper voltage?
Are the electrical connections good?
Is the contactor operating correctly?
Is the capacitor good?
Is the compressor winding resistance reasonable?
Are the windings shorted to ground?
Is an internal thermal overload open?
Is a safety preventing operation?
Is the compressor mechanically locked?
Is the control system actually commanding it to run?
And if the compressor does run:
Is it actually pumping?
Is it drawing appropriate current?
What is happening in the refrigeration circuit?
The diagnosis depends on what the compressor is doing—or not doing.
Other Reasons Your Compressor May Not Be Running
Our Palm Coast call had a failed contactor.
There are plenty of other reasons a compressor may sit there doing nothing.
The capacitor may have failed
We’ve already had another Palm Coast Ride-Along demonstrate this beautifully.
On that call, the compressor was running but the condenser fan wasn’t.
The capacitor had failed in a way that prevented the fan from starting.
Capacitor failures can affect compressor operation too.
So if the compressor isn’t starting, the capacitor is one of the things we may test.
That doesn’t mean:
“Compressor isn’t running = capacitor.”
It means we test it.
The contactor may have failed
That’s what happened here.
The contactor is part of the electrical path supplying power to the outdoor equipment.
If it fails, the component downstream can’t operate normally.
Replacing the compressor wouldn’t fix that.
It would simply give us a very expensive new compressor connected to the same electrical problem.
The compressor may be out on thermal overload
This is another good example of why timing matters.
A compressor may become extremely hot and open its internal thermal protection.
Now we test it and find an open circuit.
Does that automatically mean:
“Bad compressor”?
Not necessarily.
It may be hot.
After the compressor cools, the overload may reset.
Now we need to determine why it overheated.
We’ve had a system where a severely blocked condenser coil contributed to the compressor shutting down on thermal overload.
The compressor stopping was the symptom.
The blocked condenser was the underlying problem.
A pressure or safety control may be preventing operation
Air conditioners have protections.
If the system develops an abnormal operating condition, a safety may stop the compressor.
We’ve seen high-pressure protection shut down a Palm Coast system because someone replaced a reversible condenser fan motor and configured it to spin the wrong direction.
The safety wasn’t broken.
The compressor wasn’t necessarily broken.
The system was protecting itself from another problem.
That’s why bypassing safeties isn’t troubleshooting.
There may be a control problem
The thermostat may be calling incorrectly.
A control board may have a problem.
A wire may be broken.
A safety circuit may be open.
There may simply be no command reaching the equipment telling it to operate.
Before condemning the thing that isn’t running, we want to know whether anybody actually told it to run.
There may be a power problem
Sometimes we don’t have the electrical supply we’re supposed to have.
Breaker.
Disconnect.
Wiring.
Loose connection.
Burned connection.
Electrical failure.
Again, the compressor cannot run without the appropriate power.
That sounds painfully obvious.
It’s also why we check it.
And yes, the compressor may actually be bad
Absolutely.
Compressors fail.
We’ve diagnosed them.
Sometimes they’re electrically failed.
Sometimes they’re mechanically failed.
Sometimes they run but no longer pump properly.
Sometimes they lock up.
We’re not suggesting that:
“Bad compressor diagnoses are scams.”
Not remotely.
We’re saying something much simpler:
A compressor should be diagnosed before it’s condemned.
Especially when the next conversation is:
“Would you like an estimate for a new AC?”
“They Said My Compressor Is Grounded”
That’s more specific.
And it’s something we can verify.
A grounded compressor means there’s an electrical path between the compressor’s windings and ground where there shouldn’t be one.
That’s an actual testable condition.
If someone tells you:
“The compressor is grounded,”
we can check that.
If they tell you:
“The compressor is bad because it isn’t running,”
we have considerably more questions.
Again:
Not running is a symptom.
Why isn’t it running?
“They Said My Compressor Isn’t Pumping”
Also testable.
A compressor can run electrically but fail mechanically.
In that situation, simply hearing the compressor run doesn’t prove it’s healthy.
We need to look at what the refrigeration system is actually doing.
Remember one of our recurring lessons:
Running doesn’t necessarily mean working correctly.
That applies to blower motors.
Condenser fans.
And compressors.
This Is Why We Offer Second Opinions
A major repair diagnosis can quickly become a system-replacement recommendation.
Sometimes that’s absolutely appropriate.
Sometimes we arrive for a second opinion and confirm exactly what the first company found.
There’s nothing wrong with that.
But sometimes we don’t.
And when the difference between the two diagnoses is:
Replace a contactor
versus
replace the air conditioner
it’s probably worth spending a little time verifying.
This Palm Coast homeowner wasn’t even calling us for a second diagnostic opinion.
They were calling for an estimate.
We could have measured the house.
Looked at the ductwork.
Selected equipment.
Written up some replacement options.
And gone home.
Instead, we looked at why the existing system wasn’t cooling.
Good thing we did.
The Most Expensive Part Isn’t Automatically the Failed Part
This sounds silly when we say it out loud.
But homeowners hear some version of this all the time:
“The compressor isn’t running, so the compressor is bad.”
Maybe.
But imagine your lamp doesn’t turn on.
Could the lamp be broken?
Sure.
Could the bulb be bad?
Yep.
Could the outlet have no power?
Also yes.
Could somebody have unplugged it?
Unfortunately, yes.
We don’t replace the lamp before checking whether electricity is actually reaching it.
Same principle.
Considerably more expensive lamp.
What This Means for You
If someone tells you your AC compressor is bad, that diagnosis may be completely correct.
But if that diagnosis means you’re facing a major repair or replacing the entire air conditioner, it’s reasonable to want to know how they determined it.
And you don’t need to interrogate the technician with an HVAC textbook.
A very simple question works:
“Can you show me how you determined the compressor is bad?”
There should be an answer.
On this Palm Coast call, the homeowner had already been told the compressor was bad.
They called us for a replacement estimate.
We started at the beginning anyway.
What is the system doing—or not doing?
When did the problem start?
What is actually operating?
Is the compressor being told to run?
Is it receiving the power it needs?
We followed the electrical path.
And found a failed contactor.
We repaired it.
The compressor started.
The AC ran.
And the replacement estimate became a service call.
Sometimes a service call turns into an estimate.
Sometimes an estimate turns into a service call.
Either way, we’d rather figure out what your air conditioner actually needs before we sell it to you.
Because:
“The compressor isn’t running”
and:
“The compressor is bad”
are not the same sentence.
There’s some troubleshooting required in between.