Troubleshooting Ride-Along: My AC Is Running, So Why Isn’t It Blowing Cold Air?
The thermostat says COOL.
You can hear the air conditioner running.
Air is coming out of the vents.
There’s just one minor problem.
The air isn’t cold.
So naturally:
“My AC is running, but it isn’t cooling.”
This is probably one of the most common AC complaints we get in Florida.
And there’s an important detail hiding inside that sentence:
What exactly is “running”?
Because your air conditioner isn’t one machine.
It’s several pieces of equipment that all have to cooperate.
And sometimes half of them didn’t get the memo.
Customer Complaint
“My AC is running, but it’s blowing warm air.”
We’ve had this call all over Flagler and Volusia counties.
One of the simplest versions we’ve found was a failed capacitor at the outdoor unit.
From inside the house, everything looked like the AC was running.
The thermostat was calling for cooling.
The indoor blower was running.
Air was coming from the vents.
But the house kept getting warmer.
That’s because moving air and cooling air aren’t the same thing.
Your AC Has an Inside Part and an Outside Part
We’ll keep this simple.
Your indoor unit contains the blower that moves air through the house.
Your outdoor unit contains major parts of the refrigeration system that allow your AC to actually remove heat from the house.
They have to work together.
So when you hear the indoor blower running and feel air coming from the vents, you know one thing:
The blower is moving air.
You don’t necessarily know that the entire air-conditioning system is operating.
That’s why:
“But I can hear it running”
is useful information.
It just isn’t the whole diagnosis.
What We Checked First
On this type of call, we start with the basics.
Is the thermostat actually calling for cooling?
Is the indoor blower running?
What’s the temperature of the air entering the AC?
What’s the temperature of the air coming out?
Is the outdoor unit running?
Is the outdoor fan operating?
Is the compressor operating?
Is there ice anywhere?
Are there obvious electrical or control problems?
We don’t need to start with the most expensive possibility.
Sometimes the answer is sitting outside doing absolutely nothing.
What We Found
On this call, the indoor blower was running.
That’s why the homeowner could hear the AC and feel air coming from the vents.
But when we checked the outdoor equipment, it wasn’t operating correctly.
The problem was a failed capacitor.
What’s a Capacitor?
A capacitor is an electrical component that helps certain motors in your air conditioner start and operate.
Depending on the equipment, the outdoor fan motor and compressor may rely on a capacitor.
When it fails, you can end up with some strange combinations.
The indoor blower might still run.
The thermostat might still say COOL.
You might still feel plenty of air coming from the vents.
But the outdoor equipment responsible for actually making that air cold may not be operating.
So from the living room:
“My AC is running.”
From outside:
“Not all of it.”
What We Did
Once we confirmed the capacitor had failed, we replaced it with the correct-rated component.
Then we restarted the system.
And we didn’t stop at:
“The outdoor unit turned on. Have a nice day.”
We verified that the equipment was operating normally after the repair.
The outdoor fan was running.
The compressor was operating.
And most importantly, the system was actually cooling again.
Because replacing the failed part isn’t the objective.
Restoring proper system operation is.
The Verdict
The AC wasn’t blowing cold air because only part of the system was operating.
The indoor blower was moving air through the house, which made it seem like the AC was running.
But the outdoor equipment wasn’t operating correctly because of a failed capacitor.
Once the capacitor was replaced and proper operation was verified, the system began cooling normally again.
Simple repair.
But this particular homeowner complaint can lead us in a lot of different directions.
Other Reasons Your AC Can Run Without Blowing Cold Air
This is where:
“My AC is running but not cooling”
gets interesting.
Because “running” can mean a dozen different things depending on what the homeowner can hear or see.
The outdoor unit may not be running at all
This is one of the first things worth checking.
The indoor blower can run independently of the outdoor equipment.
So if you’re getting room-temperature air from the vents, take a look outside.
Is the outdoor unit running?
Don’t take it apart.
Don’t stick anything inside it.
We’re just looking and listening.
If the indoor blower is running but the outdoor unit is completely silent, that’s extremely useful information.
Now we start figuring out why.
The capacitor may have failed
That’s what happened on this call.
Capacitors fail.
And depending on what failed and how the equipment is designed, the compressor, outdoor fan or both may not operate correctly.
The good news is that a failed capacitor is often a relatively straightforward repair.
The important part is actually testing it rather than replacing components because:
“Probably the capacitor.”
Probably isn’t a measurement.
The outdoor fan may not be running
The outdoor unit has to get rid of the heat your AC removed from inside the house.
That’s one of the jobs of the condenser fan.
If that fan isn’t operating properly, pressures and temperatures can become abnormal and the system may stop cooling correctly or shut itself down.
The fan motor could be bad.
A capacitor could be involved.
There could be an electrical or control issue.
Again:
Fan isn’t spinning.
Useful symptom.
Not yet a diagnosis.
The compressor may not be running
This one’s a bigger deal.
The outdoor fan can sometimes run while the compressor doesn’t.
From ten feet away, the homeowner hears the outdoor unit and reasonably assumes:
“It’s running.”
Technically, something is.
But without the compressor operating, we’re not doing much air conditioning.
Now we need to determine why the compressor isn’t running.
Electrical problem?
Failed capacitor?
Control issue?
Safety condition?
Failed compressor?
Those are very different conversations.
The system may be low on refrigerant
Yes, refrigerant makes the list.
But your air conditioner doesn’t normally consume refrigerant.
If the system is actually low, we want to know where it went.
We’ve had a great example of this on a seven-story beachfront building.
The system had been losing refrigerant, and two other technicians had already been involved.
Instead of assuming which component was leaking, we isolated the indoor equipment, outdoor equipment and refrigerant lines.
Then we pressure-tested them separately.
The equipment held pressure.
The refrigerant piping didn’t.
We ultimately isolated the problem to the liquid refrigerant line running through the building.
That’s very different from:
“It’s low. Let’s add some.”
If your AC is low on refrigerant, adding refrigerant may make it cool again.
Finding out why it became low tells us whether we actually fixed anything.
The evaporator coil may be frozen
We just covered this one in another Ride-Along.
A frozen indoor coil can severely restrict airflow and prevent the system from cooling properly.
And the ice itself doesn’t tell us why it froze.
We’ve diagnosed freeze-ups caused by airflow problems, refrigeration problems and even a thermostat in Flagler Beach that allowed the compressor to operate without properly bringing on the indoor blower.
Same ice.
Different repairs.
The filter or airflow may be severely restricted
Sometimes the refrigeration system is actually working.
The problem is moving enough air across it and through the house.
A severely dirty filter can restrict airflow.
So can a dirty evaporator coil.
So can a dirty blower wheel.
So can ductwork.
If we can’t move enough household air through the system, comfort suffers even if the refrigerant circuit itself isn’t the problem.
Your ductwork may be losing the cold air
This one’s especially fun.
The AC makes cold air.
We measure cold air leaving the equipment.
The homeowner’s bedroom is still hot.
Where’d it go?
We’ve found supply ducts completely detached from the main trunk.
The system was cooling.
The air simply wasn’t reaching the room it was intended to cool.
We’ve also found undersized ducts, crushed flex, poor duct layouts and inadequate return-air pathways.
Sometimes:
“My AC isn’t cooling”
really means:
“My AC is cooling somewhere I don’t live.”
Attics appreciate the donation.
Homeowners generally don’t.
The condenser coil may be extremely dirty
Your outdoor unit needs to reject heat.
If the condenser coil becomes severely restricted by dirt and debris, it can’t do that as effectively.
That can hurt system performance and create abnormal operating conditions.
Cleaning a condenser coil isn’t going to fix every poorly cooling AC.
But equipment condition is part of the diagnosis.
The thermostat may be causing a control problem
Don’t underestimate the thermostat just because it’s hanging innocently on the wall.
We’ve already found one in Flagler Beach that wasn’t properly turning on the indoor blower while allowing the compressor to operate.
Thermostats and control wiring can cause all sorts of strange operating sequences.
The display saying COOL tells us what the thermostat thinks it’s asking for.
We still verify what the equipment is actually doing.
The refrigerant metering device may have a problem
This is where something like a TXV can enter the conversation.
The metering device controls refrigerant entering the indoor coil.
If it isn’t feeding properly, cooling performance can suffer.
But just like our frozen-coil article:
“My AC isn’t blowing cold”
is not a TXV diagnosis.
Before condemning a metering device, we want airflow verified and actual refrigeration measurements supporting that conclusion.
The AC may actually be cooling normally
This one matters.
Sometimes we arrive expecting to find a broken system and discover:
The AC is working.
Then we have to look at the house and the conditions.
Maybe it’s an extremely hot afternoon.
Maybe doors have been open.
Maybe a large number of people are inside.
Maybe the house has significant heat gain.
Maybe there’s an insulation or infiltration problem.
Maybe the thermostat was just lowered from 80°F to 70°F and the homeowner expected the house to become 70°F approximately six minutes later.
Air conditioners aren’t microwaves.
The fact that the house hasn’t reached the thermostat setting yet doesn’t automatically mean the equipment isn’t producing cold air.
That’s why we measure.
A Simple Thing You Can Check Before Calling
If your thermostat says COOL and air is coming from the vents but it doesn’t feel cold, look at the outdoor unit.
Is it running?
That’s useful information.
Then check your filter.
If it’s completely plugged, that’s useful too.
And if you happen to have a thermometer, you can compare the air temperature at a return grille with the air coming from a nearby supply vent.
You don’t need to diagnose the system.
Just tell us what you’re seeing:
“The indoor fan is running, but the outdoor unit isn’t.”
Or:
“Both units are running, but the air coming from the vents isn’t cold.”
Those two statements can send our investigation in very different directions.
Don’t Start Adding Refrigerant Just Because the Air Isn’t Cold
This is the cooling version of:
“Frozen coil? Must be low on refrigerant.”
Maybe it is.
But warm air from the vents can be caused by a failed capacitor, compressor problem, outdoor fan problem, control issue, airflow restriction, frozen coil, refrigerant leak, metering problem or something else entirely.
Adding refrigerant to a properly charged system doesn’t fix any of those.
It creates another problem.
We know because we’ve also been called behind overcharged systems.
More refrigerant does not mean more cold.
Refrigeration systems are annoyingly particular about these things.
What This Means for You
If your AC sounds like it’s running but the air coming from the vents isn’t cold, don’t assume the entire system is operating.
Your indoor blower can happily move room-temperature air around the house while the outdoor half of the air conditioner is doing absolutely nothing useful.
That’s what happened on this call.
The homeowner wasn’t wrong when they said:
“My AC is running.”
Something was running.
The failed capacitor meant the outdoor equipment wasn’t operating correctly, so the system wasn’t actually cooling.
Another house with the exact same complaint could have a failed outdoor fan.
A compressor problem.
A refrigerant leak.
A frozen evaporator.
An airflow restriction.
A duct problem.
A thermostat problem.
Or yes, even a TXV problem.
From the couch, they can all sound remarkably similar:
“The AC is on, but it’s hot in here.”
That’s the symptom.
Our job is figuring out which part isn’t doing its job.
Because the symptom isn’t the diagnosis.