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AC Running But House Won't Get Below 78 Degrees
in Fort Lauderdale, FL
A common complaint in Fort Lauderdale from June through September is that the AC runs all day and the house still sits at 78 or 79 degrees. Sometimes it's the system. Sometimes it's the house. A unit that was sized for a well-insulated home loses the battle fast in a South Florida home with old windows, poor attic insulation, or sun hitting the roof all afternoon. You need to know which problem you actually have before spending money on repairs.
Quick Answer
When your AC runs nonstop but can't reach your thermostat setting, the system is undersized, losing refrigerant, or the house itself is letting in too much heat. Fort Lauderdale heat index days above 100 degrees can overwhelm a system that was barely big enough to begin with. A tech can measure how much cooling the system is actually delivering versus what the house needs. Call (754) 354-3070 to get it checked.
Telltale Signs
Warning Signs to Watch For
- Thermostat set to 74 or 75 but house never gets below 78
- Outdoor unit and air handler run continuously with no breaks
- The hottest part of the house is under a west-facing roof or near large windows
- Attic feels extremely hot even in the evening hours
- System is more than 15 years old
- House has single-pane windows or original 1980s sliding glass doors
Root Causes
What Causes AC Running But House Won't Get Below 78 Degrees?
Undersized or Aging Equipment
An AC system is sized in tons, meaning how much heat it can remove per hour. If the system was undersized at installation, or if it's lost efficiency over the years, it simply can't keep up. Systems installed before 2006 in Fort Lauderdale often don't meet current efficiency standards and fall further behind as they age.
The Fix
Load Calculation and System Sizing Assessment
A tech performs a Manual J load calculation, which measures how much cooling your specific home actually needs. That tells you whether the system is undersized or just worn out, and how much capacity a replacement would need to have.
Excessive Heat Gain Through Attic or Windows
If the attic has less than 6 inches of insulation, heat radiates through the ceiling into the living space faster than the AC can remove it. This is common in Fort Lauderdale homes built before 1990 in neighborhoods like Riverside Park and Edgewood, where original insulation was minimal.
The Fix
Attic Insulation and Air Sealing
Adding blown-in insulation to bring the attic up to current South Florida standards reduces the heat load on the AC system significantly. It's one of the most cost-effective changes you can make to help an AC system keep up.
Low Refrigerant Reducing Capacity
A system low on refrigerant loses cooling capacity. It runs constantly because it can never fully satisfy the thermostat. The system might blow cool air that's not quite cold enough to win against afternoon heat pouring into the house through windows and walls.
The Fix
Refrigerant Leak Repair and System Recharge
A tech finds and repairs the leak, then recharges the system to the manufacturer's specification. A properly charged system has its full cooling capacity restored and can usually reach the thermostat setting again.
Self-Diagnosis
Which Cause Applies to You?
Check the signs you're observing to narrow down the likely root cause before your inspection.
| What You're Seeing | Undersized or Aging Equipment | Excessive Heat Gain Through Attic or Windows | Low Refrigerant Reducing Capacity |
|---|---|---|---|
| House is comfortable at night but never cools down in the afternoon | |||
| System runs nonstop and house stays about 4 to 5 degrees above setpoint | |||
| Problem got worse gradually over several seasons | |||
| Attic feels extremely hot even with the AC running | |||
| System is original to a house built before 1995 | |||
| Air from vents is cool but not cold |
Free Inspection
Get a Diagnosis in Fort Lauderdale
An on-site inspection is the only way to confirm which cause applies to your property. Free, no obligation.
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Serving Fort Lauderdale & surrounding areas
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