It's 94 degrees outside, the air handler is humming, and yet the house just will not cool down. When your air conditioner stops cooling in South Florida, it is not a minor annoyance — it is the difference between a comfortable evening and a miserable, sweaty night. The good news: a lot of "my AC isn't cooling" calls trace back to a handful of common, often inexpensive causes, and a few you can check yourself in under a minute.
This guide walks you through exactly what to look for, in the order a professional technician would check it — from the two-second fixes to the signs that mean it's time to call someone out. We repair these systems every single day across West Palm Beach and the Treasure Coast, so everything below is what we actually see in the field, not generic internet advice.
Start Here: 60-Second AC Triage
Before you assume the worst, run through this quick checklist. It rules out the simplest causes first.
- Is the thermostat set to COOL and below room temperature? Bump it down 3–4 degrees and listen. It sounds obvious, but a thermostat knocked to "fan" or "heat" is one of the most common calls we run.
- Is the outdoor unit (the big box outside) actually running? Walk outside. If the fan on top is spinning and you feel warm air blowing up, the system is trying. If it's silent or just humming, that points to an electrical issue — keep reading.
- Did a breaker trip? Check your electrical panel for an AC breaker that's flipped to the middle or "off" position. Flip it fully off, then back on. If it trips again immediately, stop and call a pro — that's a real fault, not a fluke.
- Is air actually coming out of the vents? Weak or no airflow points to a filter, a frozen coil, or a blower problem. Strong airflow that simply isn't cold points to refrigerant or the compressor.
Those four checks tell you which branch you're on. Now let's go through the actual causes.
The 8 Most Common Reasons Your AC Isn't Cooling
1. A Clogged Air Filter
This is the number-one cause of an air conditioner that's running but not cooling — and the easiest to fix. A filter caked in dust chokes airflow across the evaporator coil. The system runs and runs but can't move enough air to cool the house, and in bad cases the coil freezes solid.
DIY check: Pull your filter. If you can't see light through it, replace it. In South Florida's dust and humidity, filters need changing every 30–60 days, not the "90 days" printed on the package.
When to call a pro: If a fresh filter doesn't restore cooling within a few hours, something downstream is wrong.
2. Thermostat Problems
Sometimes the AC itself is fine — the thermostat is failing to send the "cool" signal. Dead batteries, loose wiring, or a thermostat reading the wrong temperature will all leave you warm.
DIY check: Replace the batteries. Make sure it's set to COOL, not FAN. If the screen is blank or behaving erratically, that's your culprit.
When to call a pro: Intermittent cooling, a thermostat that won't hold a setting, or wiring you're not comfortable touching. Our thermostat repair team handles these quickly, including smart-thermostat upgrades.
3. Outdoor Unit Won't Start (Capacitor or Contactor)
If the inside is running but the outdoor unit is dead or just humming, the most common cause — especially here on the coast — is a failed start/run capacitor or a pitted contactor. Salt air and relentless heat kill these parts early.
DIY check: Listen at the outdoor unit. A hum with no fan spin, or a clicking that never starts the unit, is a classic capacitor symptom.
When to call a pro: Always, for this one. Capacitors store a dangerous charge and should only be replaced by a technician — but the upside is it's usually a fast, affordable repair when caught early.
4. A Frozen Evaporator Coil
Counterintuitive but common: a block of ice on your indoor coil will stop your AC from cooling. It's caused by restricted airflow (that dirty filter again) or low refrigerant. You might see ice on the copper lines near the air handler or water pooling as it melts.
DIY check: Turn the system to OFF and set the fan to ON to help the ice thaw. Replace the filter. Do not run cooling on a frozen system — you can burn out the compressor.
When to call a pro: If it freezes again after thawing, you likely have low refrigerant or a deeper airflow problem.
5. Low Refrigerant or a Leak
Your AC doesn't "use up" refrigerant — if it's low, there's a leak. Low refrigerant means the system can't absorb heat from your home, so it runs constantly while the house stays warm and humid.
DIY check: None that's safe or legal — refrigerant is federally regulated. Warning signs are hissing or bubbling sounds, ice on the lines, and a system that runs nonstop without cooling.
When to call a pro: Always. We find and fix the leak first, then recharge — simply "adding more Freon" without sealing the leak is a waste of money. See our AC leak repair service.
6. Dirty Condenser Coils
The outdoor unit dumps your home's heat into the outside air through its condenser coils. When those coils are blanketed in dirt, grass clippings, and salt residue, the system can't release heat — so it can't cool. This is extremely common in South Florida yards.
DIY check: Look at the outdoor unit. If the fins are coated in gunk or smothered by shrubs, that's a problem. Gently rinse with a garden hose (power off) from the inside out, and clear two feet of space around the unit.
When to call a pro: If cleaning doesn't help, the coils may need professional cleaning or the system may be low on refrigerant.
7. A Clogged Condensate Drain Line
Florida humidity pulls gallons of water out of your air every day, and that water exits through a condensate drain. When the line clogs with algae, a safety float switch shuts the system down to prevent water damage — leaving you with no cooling and, often, no obvious reason why.
DIY check: Look for standing water in the drain pan or near the air handler. A wet/dry vac on the outdoor drain line end can clear a minor clog.
When to call a pro: If the system won't restart after you clear visible water, or you keep getting repeat clogs. This is also a core part of routine AC maintenance.
8. A Failing Compressor or an Aging System
The compressor is the heart of your AC. When it fails — common in systems past the 10–12 year mark in our punishing climate — the system runs but produces little or no cold air. A hard-starting compressor, breakers tripping, or warm air despite everything else checking out all point here.
DIY check: None. This is a major component.
When to call a pro: Immediately. On an older system, a failed compressor is the moment to have an honest repair-versus-replace conversation — which we'll walk through with real numbers, never pressure.
"It's Running But Not Cooling" — the South Florida Factor
Plenty of homeowners tell us the same thing: "The AC is running, but the house just won't get cold." In our climate, three local realities make that worse than almost anywhere else in the country.
- Salt-air corrosion. Homes near the Intracoastal and the coast — from Singer Island to Hutchinson Island — sit in salt air that corrodes condenser coils and electrical contacts faster than inland. That corrosion quietly steals cooling capacity long before the system dies outright.
- Humidity load. A correctly working AC has to remove enormous amounts of moisture here, not just heat. If your system is undersized, low on refrigerant, or struggling, it will read "72" on the wall yet feel sticky and warm — because it can't keep up with the latent (humidity) load.
- Thunderstorm power surges. Near-daily summer storms cause voltage spikes that fry capacitors and control boards. A unit that "just stopped" after an afternoon storm is a story we hear all season.
This is also why a system that limps along in spring suddenly can't cope in July: the heat and humidity load doubles, and any underlying weakness gets exposed.
Quick Answers to Common AC Questions
What is the "3-minute rule" for an AC? After your AC shuts off, wait at least 3 minutes before turning it back on. Restarting too fast can damage the compressor because refrigerant pressures haven't equalized. Many modern thermostats build in this delay automatically.
What is the most common reason an AC stops cooling? A dirty air filter, hands down — followed by thermostat issues and a failed capacitor. The simple, cheap causes really are the most frequent.
What is the "$5,000 rule"? Multiply your system's age by the estimated repair cost. If the number tops $5,000, replacement is usually the smarter financial move. A 12-year-old unit needing a $500 repair (12 × 500 = $6,000) is a strong candidate to replace.
Why is my house hot when the AC is on? If air is blowing but it isn't cold, suspect refrigerant, a dirty condenser, or a failing compressor. If the air is cold but the house still won't cool, suspect undersizing, duct leaks, or insulation — common in older West Palm Beach homes.
When to Call Kyzar
Some of the checks above you can safely do yourself — swap the filter, reset a breaker once, thaw a frozen coil, rinse the condenser. But if the cool air doesn't come back, you're in refrigerant, electrical, or compressor territory, and that's where a licensed tech saves you money and protects your equipment.
We run same-day diagnostics out of two local offices, so help is genuinely nearby:
- West Palm Beach & Palm Beach County: AC repair in West Palm Beach
- Port St. Lucie & the Treasure Coast: AC repair in Port St. Lucie
We diagnose the real failure, explain it in plain language, and give you honest options — repair when it makes sense, replace only when it truly does. Book online in 7 seconds or call and we'll get a technician headed your way.
Frequently Asked Questions
Why is my AC running but not blowing cold air?
The most common causes are a dirty air filter restricting airflow, low refrigerant from a leak, dirty condenser coils that can't release heat, or a failing compressor. Start by replacing the filter and checking that the outdoor unit's fan is spinning. If cold air doesn't return within a few hours, it's time for a professional diagnosis.
Can I fix my AC not cooling myself?
You can safely handle the simple causes: replacing a clogged filter, resetting a tripped breaker once, thawing a frozen coil, replacing thermostat batteries, and gently rinsing the outdoor condenser. Anything involving refrigerant, capacitors, or the compressor should be left to a licensed technician — those carry safety and legal risks and require specialized tools.
Why does my AC freeze up in Florida?
A frozen evaporator coil is caused by restricted airflow (usually a dirty filter or blocked vents) or low refrigerant. Florida's humidity accelerates it. Turn the system off, set the fan to ON to thaw the ice, and replace the filter. If it freezes again, you likely have a refrigerant leak that needs professional repair.
How quickly can you come out if my AC stopped cooling?
In most cases, same day. We dispatch locally from our West Palm Beach and Port St. Lucie offices, so we can typically reach homes across Palm Beach County and the Treasure Coast within hours of your call — often faster during the peak summer months when speed matters most.
Is it better to repair or replace an AC that won't cool?
If your system is under 10 years old, repair is almost always the right call. If it's older and facing a major repair like a compressor or coil, apply the $5,000 rule (system age × repair cost). When the result tops $5,000, replacement usually wins on long-term value. We'll show you the real numbers and let you decide — no pressure.
