Troubleshooting Ride-Along: My AC Is Running, But the Air Coming Out Isn’t Cold

Location: South Daytona, Florida
Complaint: AC is running, but the air coming from the vents isn’t cold.

This one started with a complaint we’ve heard approximately four billion times in Florida:

“The AC is running, but it’s not blowing cold.”

Indoor blower is running.

Outdoor unit is running.

Thermostat says COOL.

Yet the air coming from the vents feels somewhere between disappointing and absolutely useless.

Usually we’re thinking refrigeration problem.

Low refrigerant.

Compressor problem.

Airflow.

Maybe a reversing valve on a heat pump.

Except this system had another clue:

Someone had just replaced the thermostat.

Oh.

Well that’s interesting.

What Changed?

Whenever a problem appears immediately after somebody works on the system, one of our first questions is:

What changed?

That doesn’t mean we’re automatically blaming the previous technician.

Parts fail at inconvenient times.

Coincidences happen.

But if the AC cooled yesterday, somebody replaced the thermostat this morning, and now the AC doesn’t cool…

We’re probably going to take a pretty hard look at that thermostat before connecting twelve thousand dollars worth of diagnostic equipment.

The System Is Actually Running

We called for cooling.

Indoor blower came on.

Outdoor equipment came on.

Everything looked like it was responding.

But the supply air wasn’t getting properly cold.

So we started checking temperatures.

Something didn’t make sense.

The refrigeration system was trying to cool the air.

But somewhere along the way, that cooling was being cancelled out.

And then we found it.

The Heat Kit Was Running

While the air conditioner was cooling.

Yep.

The evaporator coil was doing its job trying to remove heat from the house…

…and the electric heat strips were immediately putting heat right back into the air.

The system was basically having an argument with itself.

AC: Let’s cool the house.

Heat kit: Absolutely not.

Both were operating at the same time.

And the homeowner was paying the electric bill for the fight.

Back to That New Thermostat

Remember our clue?

The thermostat had recently been replaced.

We checked the thermostat setup and wiring.

There was our problem.

The thermostat installation was causing the electric heat to energize during a cooling call.

So the thermostat said:

COOL

but the equipment was receiving instructions that effectively resulted in:

COOL + HEAT.

Not ideal.

Correct the Control Problem

We corrected the thermostat wiring/setup so the equipment received the proper calls.

Then we started the system again.

Cooling call.

Indoor blower starts.

Outdoor equipment starts.

Heat strips?

OFF.

Excellent.

Now check the supply air.

Cold.

Exactly what we wanted.

Why This Could Have Turned Into a Refrigerant Call

This is where symptom-based guessing can get expensive.

The homeowner’s complaint was:

“The AC runs but the air isn’t cold.”

That could absolutely be a refrigerant problem.

So imagine immediately connecting gauges and seeing something you don’t love.

Maybe somebody decides:

“You’re low on refrigerant.”

Adds refrigerant.

Air still isn’t cold.

Well.

Maybe TXV.

Maybe compressor.

Maybe we need a new system.

Meanwhile, several kilowatts of electric resistance heat are sitting inside the air handler going:

🔥 HELLO 🔥

Sometimes the first diagnostic tool isn’t the gauge set.

It’s asking:

What happened immediately before the problem started?

Electric Heat Is Not Subtle

Electric heat strips produce a lot of heat.

That’s their entire job.

They’re essentially giant electric resistance heaters installed inside the air handler.

When we’re heating the house, great.

When we’re trying to air-condition South Daytona in August?

Less great.

They can dramatically raise supply-air temperature and make a perfectly functional refrigeration system look like it isn’t cooling.

They can also use a substantial amount of electricity while doing it.

So this wasn’t just a comfort problem.

Leaving the system this way could have created a pretty exciting electric bill too.

The South Daytona Verdict

Complaint: AC running but supply air isn’t cold.

Recent work: Thermostat replaced by another company.

Indoor blower: Running.

Outdoor equipment: Running.

What we found: Electric heat kit energized during cooling operation.

Cause: Incorrect thermostat setup/wiring.

Repair: Corrected thermostat control configuration.

After repair: Heat strips remained off during cooling and normal cold supply air returned.

Refrigerant added?

No.

TXV replaced?

No.

Compressor condemned?

No.

We stopped the air conditioner from heating the air it had just cooled.

Turns out that helps.

The Bigger Lesson

When your AC is running but the air isn’t cold, there are plenty of possible causes.

But troubleshooting isn’t just about knowing every possible failure.

It’s about noticing clues.

And one of the best clues a homeowner can give us is:

“It started right after somebody changed something.”

That doesn’t prove what went wrong.

But it’s an excellent place to start looking.

On this South Daytona service call, the refrigeration system wasn’t the enemy.

The AC was actually trying to cool.

Unfortunately, the heat kit had apparently not received the memo.

Cooling works considerably better when we don’t run the heater at the same time.